Powerlifters Aren't Powerful, They're Forceful: a note on what we're measuring with velocity based training (spoiler: it's velocity)

• This whole article is esoteric. This is probably as far in depth I'm going to get with power because it really isn't a huge factor for powerlifting
• Even though there are strong correlations between barbell velocity and several other variables (load, intensity, exertion, your favorite skittles flavor, etc), you're not a Doctorate of all the Strong Things for using VBT. You're just another dude that collects numbers
• There is no gold standard of velocity based training's metrics. It's still kind of up for debate, especially if you're using it for things like estimating power, force, work, and capacitive magnetic reactance. Please don't use your VBT device for capacitive magnetic reactance
• Basically, the information we get from VBT, while potentially powerful, really isn't that large of a step forward than quantifying our understanding there's an inverse relationship between %1RM and the volume (sets X reps X weight). It's better than the traditional programming model (opinion), but not that much
• There are known knowns. Things that we know that we know. There are known unknowns. Things that we know that we don't know. But there are also unknown unknowns. Things that we don't know that we don't know. And ultimately: the absence of evidence is not the evidence of absence prolly means we're guessing
• I really don't follow up on the things that I plan to do, but here's a page worth of shit posting based on the things I've been reading. No more planned posts.

Introduction

In the first post of this series, I did several comparisons of 3 different sensors for variations of the squat, bench press, and deadlift. In that post, my comparison measure was 2D video analysis. The obvious red flag here is that of all the comparison measures - 2D video analysis sucks. But this brings into question as to what's an appropriate criterion measure, or gold standard of comparison, when we talk about velocity based training devices. Also, what about the other metrics most units pull besides velocity? How about force, power, and work?

Having these criterion measures is important. For sake of explanation, hydrostatic weighing is the gold standard for body composition (technically it's potassium counting, but we fucked that up with the nuclear age). Bioelectrical impedance, waist-neck approximations (the "Navy equation"), DXA, and BodPod are all compared to underwater weighing typically when evaluating them for accuracy and reliability. You can compare one of these methods to another besides hydrostatic weighing (IE: the navy equation vs bod pod), but the comparison always relates back to the criterion measure - underwater weighing. A good criterion measure will be highly accurate and reliable. Accurate meaning it measures close to the actual value and reliable meaning it will reproduce that value with relatively low variance.

Think of it like three weather men. One is always 10 degrees warmer than he forecasts, but it's consistent. The other one is usually within 5 degrees of the actual temperature, but could be lower or higher. The last one is always 5 degrees above. While he's as accuracte as the 2nd weatherman, he's also more consistant. Actually this is a horrible analogy. No one gets their weather forecast from the nightly news anymore. Moving along

It's a common remark that all you need to know about lifting you can learn in a physics textbook. Yet the same people that say these sorts of things have "power" days in their routine that aren't necessarily powerful or are basically flying in the face of some basic mechanics. Volume is a shorthand metric we use, as is intensity. The underlying variable for volume is work, and intensity is force relative to a maximum. These things aren't necessarily intuitive though, so we shorthand volume with the number of reps by weight, distance, laps, whatever.  Likewise, peak force isn't easily quantifiable, so we just use a ratio relative to our 1 repetition maximum. There's really nothing wrong with that until you start implying that variable resistance (bands, I'm talking about bands) accelerated as fast as possible has a meaningful difference from doing a 1RM. You really wouldn't know that any more than you would you know your altitude just by feel. It might sounds like I'm taking shots at the usual suspects, but really every coach needs to make some assumptions about mechanics as they relate to training because measuring all these things aren't meaningful. And ultimately, the body's response to training isn't exactly required to make sense. Sometimes it just works, albeit sometimes in spite of and not because of the training method. We need to be honest about our instruments' and methods' limitations. I do this all the time with VBT when I talk about deadlifts. Mean concentric velocity has less meaning with deadlifts.

So this will highlight the insufficiency of certain velocity based methods.

Video Analysis as a Criterion Measure of Velocity and Power

Video analysis is probably one of the old school reliables for velocity. Not the best, but has been the mainstay since before VHS. You can record something with a ruler in the frame and use the frame rate and distance of that scale to get a general idea of the rough edges of the movement. Folks have been doing this for sprinters, weightlifters, and all sorts of olympic sports for years. Nowadays, we've opened that up to the masses through things like Dartfish, Coach's Eye, Kinovea, and Tracker. These are all entry-level tools and very valuable.

What you lose in 2D video analysis is essentially depth. You can get horizontal and vertical distance, but getting a measurement outside of your initial measurement is sketchy. An easy way of thinking about this is weight plates. An Olympic weight plate is supposed to be 0.45 meters in diameter. So when analyzing bar speed, it's a pretty easy measure to use. Here's the information lost with 2D video though:

Ian Wilson courtesy of the Hook Grip instagram account.
Both of these plates are the same size when viewed in the same depth,
but it obviously fails when viewed in this objective

The key takeaways are to analyze objects in the same plane, film horizontally and vertically perpendicular to the plane you plan to measure, and have a known unit of measure (a ruler within frame, standardized disc sizes, etc). Some other issues come up concerning video quality and frames per second. Thirty frames per second are going to lose a lot of information from frame to frame, whereas 120 is going to capture a large amount. Likewise, better video quality is going to give you clearer edges to measure. Some phones that film in slow motion are capable of capturing 240 frames per second at a lower quality, so you have to manage clarity of the video against the number of frames you need. The right way to go about this would be to buy something that puts GoPro cameras to shame, but that's not a realistic solution for coaches living in the real world.

Now it's important to note that programs like Kinovea have been validated when it comes to simple movements, and we can describe powerlifting as simple movements. We can postulate about how the bench press is a full body movement and how all three lifts hit all of the things and yada yada. It's simple. There's an upward motion and a downward motion. That's simple. We only make it complicated by focusing on the minutia. Powerlifting is stupid simple, stupid.

A step up would be 3D motion analysis. Using an array of cameras about a stage, we can track movement in three dimensions. This helps understand more complicated movements as well as sort out the axes that affect rather simple movements. Much like with 2D video analysis, you're going to have a known unit of measure within the frame during initial calibration. This helps the software understand position, length, and movement reliably. The great advantage of 3D video analysis is you can track multiple points of interest. If you're solely interested in barbell velocity, you can place a reflective marker at different points along the barbell and body to track that. So not only can you track velocity of the barbell, but you can see the angular acceleration of each joint during phases of the movement. That angular acceleration of all the joints in the movement translates to vertical and horizontal movement by the bar.

Video analysis of this scale isn't practitioner friendly. It's cost prohibitive, technically demanding, and largely just more trouble than it's worth unless you're doing research. On the research front, Lake et al have heralded the use of a force plate and video analysis as a criterion measure to determine power. The force plate measures force and the video analysis measure velocity, so you get the all the components you need. Sort of.

Let's bring it back to barbells though, since that's the sort of thing powerlifting does. The issue with barbell based VBT is that bar speed isn't necessarily the velocity of the center of mass. There's debate on how you determine that, but this shows that divergence:

Lake et al's article gets straight to the business with the title: Barbell kinematics should not be used to estimate power output applied to the Barbell-and-body system center of mass during lower-body resistance exercise. I'll refer back to this later.

But how consequential is that? Volume isn't a true measure of work and intensity isn't a true measure of force, but they have been good enough to be usable. Especially when it comes to powerlifting, the difference between system center of mass (the barbell and body system) becomes less consequential the heavier you lift. As a male, your center of mass is near your belly button, and the more plates you stack on, the closer it will move towards the position of the bar. And that center of mass is going to change not just with load, but the position of your body. When this is consequential is when we're dealing with light loads: such as those done to develop power. It's a good thing the objective of powerlifting isn't about demonstrating the most power. You're really getting a metric of barbell power with most units and rough approximations of system (bar and body) for others.

One of my favorite past-times is meme-ing fitness industry stills from YouTube

Bar Tethers

Linear position transducers (what I keep calling tethered VBT devices), are the most common measurement of bar speed. Most device validations are in comparison to other, older LPTs. Some of the most common comparisons seem to be to Optitrak, Tendo, and T-Force. Just because it's the most common doesn't necessarily mean it's the most valid though. We're essentially comparing one device's yardstick to another's and seeing how close they are to one another and the frequency that the difference is the same. As long as we can keep comparing to that same yardstick, it doesn't matter. Ideally, you want accuracy and reliability, but short of that reliability across all your feasible working intensities is most important. So if a device sucks at measuring slow things, heavy things move slow, and you lift heavy things - don't do it.

Some proponents of VBT have heralded tethering devices as the gold standard. Anyone that says that is probably trying to sell a product or obfuscate what their device is measuring. As I demonstrated in the first article, it seems to be the case that tethered devices are more accurate and reliable for measuring velocity. It does not measure power or force though. To measure those things, you need force plates. You can calculate it with known masses (bar weight, body weight, etc), but it's essentially best for velocity. Everything else is approximation and calculation, and there is certainly some drift across different ranges.

I don't know how to say this better than the original author, so here it is:

"Other studies have indicated that methods that depend only on kinematic and kinetic results have limitations when used to determine power output (Cormie et al., 2007b; Hori et al. 2007). It seems that the linear position transducer technique overestimates power due to increased force output production derived from double differentiation of bar displacement. When this technique is applied also to the mass of the subject, standard biomechanical procedures are rejected in that force is determined without considering the acceleration produced through a movement (Dugan et al., 2004). Despite this limitation, our results indicate that monitoring bar velocity is a useful procedure to control load intensity in resistance exercises, as observed by other authors (Hori et al., 2007; McBride et al., 2011)" - Garnacho-Castaño

The Cormie et al paper from 2007 cited has an interesting experimental method shown here:

The key part here is the use of a force plate. The tethers are inverse mounted and it just does trigonometry to determine position across time. Both this method and the method demonstrated by Lake involved force plates. There's really no getting around actual measures of force. To put it another way, trying to use VBT devices to measure force or power is like using a thermometer to measure rainfall. Ok, not that bad, but sort of.

Another point worth mentioning is that the trigonometry used with two tethers is achieved all the same using GymAware's technology. Rather than measuring the lengths of the side of the triangle (with one unchanging known side length) determining the angles within, GymAware measures one side and an angle which gives you a measure of vertical and horizontal position (the other two sides of the triangle). All that shade you been throwing on social about trig, and now it's actually kinda useful ain't it? Trig is useful folks. Build a staircase.

It's important to point out that Cormie et al and Lake et al's method do stand in conflict to one another. To some extent, Lake is probably right that center of mass is the "real" variable we should be measuring (kind of like how work is the "real" variable for volume). At the same time, Lake does not sufficiently explain how they determine the center of mass. This isn't necessarily impossible either if you apply something like segmental densitometry (for example, DEXA gives limb weights). Without taking sides here (Lake vs Cormie), the important parts are 1) both of them point out the necessity of a direct measure with a force plate 2) both research groups have authors that have done a lot of research on powerlifters, so they're pretty damn rad.

Accelerometers

Accelerometers seem to bridge this gap to some extent, when the right inputs are used. The issue is Force. Force is a product of mass and acceleration. If we return to the issue as mentioned by Garnacho-Castaño et al, inertial sensors would seem a likely solution. If I haven't hammered the point home yet, while accelerometer technology has failed to perform on some fronts, it could be the missing link we're looking for. This is especially pronounced with power movements.

I've talked before about how you could theoretically determine velocity when an accelerometer is attached to a fixed point if you know the lifter's height. It's a rough approximation and relies on relatively normal proportions of limb length according to height and the mechanics of exercises being relatively comparable across a broad population. That method would require a certain amount of machine learning or constants and manual inputs of the lifter. At a minimum, I would think height and weight would be important to determine force and power. That said, if tethered devices clearly excel at measuring bar velocity, then they're probably the right tool for the right job.

Banyard et al down at Edith Cowan Uni used the same method that Cormie et al used and took GymAware and PUSH head to head in one of the most comprehensive comparisons. Again, these comparisons are made with a dual tether and force plate system:

Notice this is only figure 3 and 8. You should see the rest of them. Some have insisted that the difference between actual power and GymAware's power is only 10 watts. I'm seeing 100 watts. Follow the link.

If your main take away from this is that PUSH is hot garbage and GymAware is overpriced because it measures what it says it does, you're missing the point. The point here is that I'm not sure why these are currently two separate products. A combined approach using both a tether and an accelerometer could still be affordable (assuming GymAware doesn't set the price), you'd likely see additive value. Force plates are almost out of the question.  In order to cover the size you'd need for a simple movement like a squat, you're talking about an upfront investment of $600 minimum.

Just do the math. If the cheapest tether device is $200, and a force plate set up would cost $600, that's like 4 red competition plates you can't buy.

I haven't been paying terribly close attention to PUSH, but it would appear they're actually serving their market pretty well. They've implemented a new system that uses some video processing in combination with the sensor to collect different metrics. Again, this really doesn't matter for our purposes because, well, barbells. If you are using the PUSH as a powerlifter, one great feature they've implemented is velocity cut off notification. That makes it decent for hypertrophy work (because lighter=faster), but maybe not a strength. The only other VBT device I can think of that has attempted to add another input (IE: video, displacement, etc) is the Form Sensor. However, Form's altimeter really only helps to improve vertical velocity as far as I know.

Approximations aren't all that bad

Some accelerometer systems are getting their estimates of power based on the combined input of load and body weight. This sort of works, but we have to recognize it is an approximation. The issue with most accelerometers in the end is that they tend to be thrown off by sudden changes in direction, jarring not related to the movement, and Germanic talismen inscribed with the correct order of runic scripture. Ignoring some of the inadequacies there, approximations aren't too bad. 

A good example of combined measurement and constant (manual input) measures is the Powerlift App. When you break it down, the app functions as a video stop watch. It takes a video that you use as a visual reference point, you input a range of motion for that movement (which hopefully you measure appropriately), and choose start+end points for the concentric part of a movement. It's actually pretty good at it and has been validated in a lab. All the app does is convert the start+end point frame count to determine time, dividing the ROM by that time to determine mean velocity. You're not going to get peak velocity.

Side note: Powerlift is unlike many devices in that it actually stores correlations of load and velocity, as well as many other useful funtions. Most device manufacturers could take some tips from Carlos. Technically some do this, but is a sort of way that can only be reference manually - far from optimal. 

Again, with combined measures and inputs, you can improve this further. For example, if you were to take the average of your ROM from all loads over 90%, you could improve reliability near 1RM distance. You could also manually input your MVT in advanced options, but for sake of fidelity it's probably better to only use ROM input from another device you trust and video an MVT rep to keep it relative. 

Why it Matters: Science, Theory, and Methods

When I say the science, I really mean more of the mechanics - the sort of rules that things obey. There is something troublesome about scientific training. Firstly there's the fact the science does sort of exist in a vacuum. The protocols employed by science are commonly used to elicit a response, to tease out a marked difference or similarity of one treatment versus another. It really doesn't matter if it's a realistic training program (let's pretend that's the only kind of sports science for this), but one that emulates enough elements of real training protocols but has a magnitude large enough to elicit a response. Basically, most of these programs don't have ecological validity - they aren't programs that would be optimal.

Training theory on the other hand (not "scientific theory") is basically the rationale which we think training follows. This is a blend of what coaches have seen in practice and lab rats have evaluated in a laboratory setting. That connection from A to B isn't always a straight line. For example, the force-velocity curve is more based on the functional characteristics of muscle fibers. It's not necessarily the same thing when we're talking about movement created by multiple muscles and about multiple joints.

Lastly, the methods are how we choose to execute our training theories, hopefully based on the practical applications of the science. Using bands is one such methodology. I've beaten that dead horse long enough though, so let's use Orange Theory Fitness. Orange Theory Fitness markets itself as a science-based weight loss program. It sort of is. If we think of work (joules) as a proxy for energy expenditure (calories), then high volumes of energy expenditure are more obtained at lower intensities. I'm basically saying pure cardio. That's not exactly the Orange Theory Fitness training program. Secondly, there's a significantly greater magnitude of difference obtained through diet. So it's not all bullshit, but science did not divine the right answer to Orange Theory fitness and there's plenty of caveats. But science sells. Even diet programs use that tactic.

Everyone fails at marrying these three elements together, including your gurus, to some degree. With velocity based training, most of that fault comes from the science. I spent this whole article highlighting disagreement. The training theory failing comes from over-expansion of concepts like the force-velocity curve (IE: the training zones). An extension of that carries over into methods. Assuming the force-velocity curve can be made so specific in gross movements could be made even worse with the idea when adding variable resistance.

Putting it All Together

If you own a tether system, stop being so uppity. You have the most appropriate system for measuring velocity, and even that is still subject to error - even more so if it doesn't measure angle of pull. You could probably rig up two single axis system to improve vertical velocity measurement and maybe even track bar position throughout a movement, but there is no consumer level solution yet. Beyond the fact that tethers aren't appropriate for movements in three planes of motion, accelerometers do have additive value to help us better measure simple training metrics - like force, power, and work. We don't have those solutions yet, but that's likely the future. It might seem ridiculous to forecast the future like that, but given the relative utility of Accelerometer-GPS units for field practice, it's not too far off.

Velocity based training is supposed to be a method to quantify things we were making guesses about. Generally, something that's powerful was subjectively fast enough and light enough. I say subjectively because it has to be someone with some authority and experience in developing powerful athletes with movements that best mediate that training quality. That sense of what is powerful is largely a presumption. As much as velocity tells us, there's still plenty we can't nail down. Operating in this unknown area is fine though. We've been operating in the unknown using simple measures for decades. But you should probably stop taking VBT measures of power and force at face value.

#MaybeJustLiftWeights #ButHaveYouReadSUPERTRAINING

A Powerlifter's Guide to VBT Pt 5: Future Directions for Auto-Regulation Training

[Update 5/9/2017] The manufacturers have responded pretty robustly and directly. Some features I say manufacturers didn't have they actually did have - either on their premium account features or through some other way. Other features were already in the development pipeline.

Most notably, Beast reached out and told me they do provide some velocity-time graph features for the first rep of every set - which is useful for analyzing opening attempts or 1RMs. You can export on Beast - again possibly with a trainer account which I don't have. OpenBarbell also debuted a new export to CSV option. Who even knows that OB is coming out with in their version 3 release, if any changes at all.

I'm not going to edit this as every advance in the technology or science happens. I'm hella lazy. So just keep that in mind. I also apologize for the horrible formatting I did. I've tried to correct that.

[Update 5/17/2017] Both PUSH and OpenBarbell seem to have developed through different avenues. PUSH with seemingly more outreach/education and OB with a new build and promise of an updated app. OB is exporting to CSV after a few hiccups with the initial rollout, and it very clearly stores the information on a linked Google Drive account upon successful export.

INTRODUCTION

There are two avenues I'd like to see developed. The first if the most practically oriented, and that's things manufacturers and practitioners can do to bring the technology forward. The second is possible future directions for the research. For the folks on the front line, the obviously more actionable one is on the manufacturer and practitioner end. Without the research to validate our experiences though, we're essentially working by trial and error. I don't mean to fetishize what the academics are doing, but if we were limited to exactly what the practitioners were doing, VBT would probably be limited to the secret strength and conditioning manual of Missouri Football (jokes). There is some overlap between the manufacturers, practitioners, and the research. This is obvious with folks like Dan Baker working with PUSH, Bryan Mann working with GymAware, and Kabuki teaming up with OpenBarbell.

MANUFACTURERS - THE EASY SOLUTIONS FIRST

This is probably the easiest part to sort out. The private sector tends to be rapid about sorting out solutions fairly quickly. The main issue is holding some of these things back due to novelty and propriety. One of the most interesting recent advances in VBT devices that I expected more out of was Open Barbell being open source. This was different than previous devices that tried to meet the demands of the loudest and highest paying voices in the industry. These were namely strength and conditioning in sports, mostly money sports (which powerlifting is not). My original hope was that Open Barbell would have diverse application development that would run awry, much like the Google App store. This has not been the case. Meanwhile, other manufacturers seem to be porting out features that have no direct application to powerlifting and pertain more to speed and power sports.

So what do I hope to see/expect?

Possible Hardware Configuration Changes or Methods of Measurement

This section is full on nerd. You might not appreciate it, so skip to the next subheading.

This is possibly more pertinent to accelerometer systems, but it would make sense to me that additional sensors could increase the accuracy of accelerometer VBT devices. Form Lifting seems to be beating down the right track by incorporating a barometric altimeter. PUSH, on the other hand, tries to navigate the measurement by using accelerometers and gyroscopes. Using this approach, if you can get a signal on the orientation and the acceleration of the sensor, you can derive velocity data by normalizing to individuals with some simple inputs (height, weight, etc) following a basic template that teaches the data processor how to interpret the information. I haven't had hands-on experience with Form Lifting, but it would seem to me their sensor has an advantage that PUSH doesn't: movements where the rate of change in orientation of the sensor and velocity is very low. This is most pronounced in the deadlift, where the rate of displacement of the sensor is slow and orientation does not change to a significant degree. A sensor like Beast struggles with deadlifts for one common reason that many accelerometer systems do: the jostling of the bar after dropping and vibrations. The difference with Beast is it allows the user to purge repetitions. This solution is easier with faster movements like the squat and straight guesswork with a heavy deadlift.

Accelerometer systems only have so many ways to navigate this issue. One potential fix is to change sensor location. This seems to be an area where Beast has the most versatility, advertising itself as both a magnet mounted unit and a wrist-mounted unit. PUSH also uses this method by relocating the sensor for jumps (waist belt mount) and pull-ups (upper arm). Another sensor, BarSensei, seems to build their units to be more purpose driven, with accelerometer systems that are both bar mounted and medicine ball internal. 

The next solution ties into the following to some extent. One issue with the systems tends to be that they are unable to tell their position relative to the whole system that's moving (the body and the barbell). One possible fix is to give it more inputs specific to the user. For example, if the system understands orientation about the human body and how it accelerates at different angles, it could be pertinent to teach it the exact position of those pesky joints. For example, a system that assumes your trunk is 30% of your height, leg is 23%, and arm is 32% could gain from knowing what the actual lengths are so as to know how they are supposed to accelerate about the y component when functioning as a whole system. Form gets to sidestep that issue by utilizing their altimeter, but other systems have the advantage of additional inputs, like asking users to calibrate the system through measuring body segments. This is in contrast to using generalized proportions. This is most important when anthropometrics can garner an advantage in a sport, like long arms aiding deadlift mechanics.

Now that we're headed down the path of calibration, we should talk about calibration. If anyone remembers early GPS systems, they required you to do a calibration process whereby the user spun the unit across two planes and raised and lower the device. The counter-quip to this is to build a product that's fully calibrated and holds it to begin with. This might be a sound philosophy when it comes to smartphones becoming outdated every year, but I generally expect my gym equipment to last longer than that. If I had to replace my iron every year, I'd rent it through a commercial gym rather than owning a home gym. An ancillary issue is the price and/or supply can fluctuate wildly. In particular, Beast has taken forever to create an American distribution location, the price of PUSH has only increased due to increased features and development, Open Barbell sells out of stock inside of a day, and GymAware cost roughly the same as a cycle of steroids so why not go that route anyways (kidding, USAPL). Long story, short: it might be helpful to have a calibration feature built-in on the operator end.

Load-Velocity Mapping Built In

PUSH essentially has this built in, but it doesn't really make it useful. For whatever reason, you're perfectly able to run a 1RM-VBT estimate through an app feature, but that information just stays in your dashboard being as useless as calf raises for your bench press. Instead, you just get this feature that lets you dictate a really broad range of velocities for a specific training quality (strength, speed-strength, etc). Below is an example of PUSH's built in 1RM estimate test.

I would like to see a feature that allows you to map Load-Velocity. Ideally, I would like to see the app conduct a reverse lookup on a build-up set (as you're trying to find your working weight) and return an approximate estimate of your %1RM. Even better would be the ability to set a %1RM and have the device alert you when you're within acceptable tolerances of the corresponding velocity. With this one feature, half the reason to use templates like I do disappears. Chances are, if it's something I do in MS Excel, there's a really easy way to make it happen in an app.

I don't shame people often, but the industry deserves to be shamed on this fact. Some VBT devices have been on the market for years now. The research and practitioners have been pretty clear on the need for L-V tables to make it individually actionable. Instead, manufacturers have sidelined this simple implementation for others. This is a letdown, especially for manufacturers that have had e1RM features since day one. Failing to capitalize on this relegates some VBT devices to cocktail party tricks that have little to no effect further down the road.

Update 8/28/2017: Even though I've railed against video analysis systems in the past, the Apple app Powerlift actually does this. Furthermore, it has been validated by Carlos Balsalobre-Fernández. There are some limitations, but it's still good in a limited way. To set up your load-velocity profile, you have to know the length of the movement. To get this, I cheated and used the readouts from Open Barbell's ROM measurement (btw: my squat is 666 mm). You can build out your load-velocity profile and then measure the velocity of individual reps. If I were using it in real time, I would probably just ramp up to 80% actual 1RM, measure the velocity, and use the estimate + basic algebra to figure out the day's 1RM and the working weight for the day. This might not be optimal given recent findings, but I could see this working it's way into the app shortly.

Also, I wouldn't get hung up on the fact that Powerlift's velocity differ from another device if you use one. What's important is reliability, not so much accuracy. The key part is to try to conduct your 1RM predictions from the same camera angle, height, and distance as your load-velocity mapping session.

Load-Exertion Mapping Built In

Likewise, a Load-Exertion (L-E) or built in rep to failure (RtF) table would be just as useful. While I tend to follow velocity loss, there are practical limitations to this simplistic approach. A built in L-E table would give you a good indicator to follow in real time, alerting you to when you're 1-3 reps away from failure. A L-E table establishes what your last rep in the tank, 1-3 reps left in the tank, and so on. Rather than working based on velocity loss, which gives us a very rough guideline, we can dial it into alerts based on how far away from failure we want to be: 1-4 reps depending on the training goal. Granted, RPE ratings essentially do this for us, but this feature alone could increase the cross talk between RPE and VBT. This provides a very clear objective read on reps in reserve that can be used in real-time for VBT users or to validate RPE's assertions on their ratings.


To make L-E feature built in, all that would be required would be RtF sets at two intensities, like 75% and 85%. Those RtF sets could also feed forward into e1RM tests to establish MVT and a more accurate estimate of 1RM.


How about this for a really easy feature: any time you set a new record low velocity, ask if the user wants to designate that as their MVT. Make it something that can opted in or out of, just in case it wasn't a full rep, it didn't meet the criteria for a technically proficient lift, or was purposely moved slow according to tempo prescription.

The "Velocity Zones" Sucks

This one thing is the most important factor IMO to make VBT data fluid and actionable.

Firstly, the velocity zones for are very dependent on the exercise and athlete, depending on the training outcome. You could probably find ideal zones for different exercises for different training qualities for different types (most specifically heights) of athletes. This sounds very time-consuming though and doesn't really help the user. KISS: keep it simple, stupid. That, or I guess you can exploit the fact you have a user database with self-selected data, do a database analysis controlling for height and exercise classification, and multiply it by the squared cosine of making a simple solution harder than it needs to be.

This one thing is the most important factor IMO to make VBT data fluid and actionable.

Granted, there is a way to do this through program creation with some apps and webportals, if you can get over the fact that every system that has a program creation guide as rigid as frozen dog poop. Here's an idea: let me designate the velocity zone myself while using the app. Specifically, let me choose a velocity, plus or minus a given percentage of that velocity for an initial target, and an acceptable stopping point (either a specific velocity or a certain percentage of velocity loss).

Surprisingly, Beast for all it's
lackluster does have this simple
feature. Not exactly on the mark, but
why is this not common to all?

It seems pointless, but when you consider that rows and pull ups have a high MVT, according to the velocity zones, you can hit a 1RM without ever really working within the "absolute strength" zone. If we had this one feature, you wouldn't have to see the screen for real-time feedback. This one thing is the most important factor IMO to make VBT data fluid and actionable. I'll keep saying that in hopes that some manufacturers pick up on the point that this needs to be a basic feature.

Athlete Monitoring - Daily Readiness Testing

Take for example a traditional Sheiko program. Something that has you squat for a certain number of reps, gives you a brief reprieve by benching, then has you do an assistance version of the squat. If you have a very, very clear training priority in the day (squat, in this example), you want to know how beat up you are. One of the more popular ways of checking your daily readiness is by doing a squat at a standardized load. I usually use 60% of my last official 1RM (not my daily 1RM). I call this my "cold start" since I do it first without any warm up or practice reps (maybe air squats or some body weight variant). If that weight moves slower than my L-V tabled velocity, I know I'm carrying a bit of fatigue around. This doesn't stop me from training, but it prepares me for what to expect. If it moves faster, I can probably stack more plates on the bar that day.

Not terribly recently, Dan Baker suggested a standardized load of 80% 1RM IRC. The smallest worthwhile difference in determining deviation from readiness was 0.04 m/s difference from baseline. If you can move that faster, you're stronger (at least that point in time). More than 0.04 m/s difference in terms of drop in velocity means fatigue is inhibiting your readiness. This seems to come from his coaching experience and possibly data from his previous studies (the Oceania strength and conditioning community is awesome like that). YMMV

With enough measurements, you should have a baseline reading (think of it like a rolling average). With that baseline, you'll also have a gauge of what is abnormally above or below your baseline. This is the same kind of principle that Heart Rate Variability uses on a global level, but this gives you a direct read on local neuromuscular readiness. Again, this is something you can do through Excel using something like basic Z-scores or percent difference from baseline. Here's a fictional example:

Standard traffic light system. Green means increase training
load, yellow means normal training load, red means decrease
training load. Arbitrarily set at a difference of 10%

The hardest part of athlete monitoring is finding a way to make it unobtrusive and have additive value to the training process. It's already a bother to make an excel sheet to accompany an app to accompany a device to accompany a barbell. How is this not a thing? Manufacturers that want to sell their product like it pertains athlete monitoring should put something in the fine print that says, "but you figure that part out on your own, hoss." 

Graphs Against Time

Given the amount of samples most of these devices collect per second, it would be really helpful and plausible to have velocity-time graphs or displacement-times graphs much like what is shown here:

These seem minor, but in powerlifting it really helps validate struggling areas of your lift. For example, a change in the slope of displacement over time can show you the slow parts of your lift. That slow part of your lift is likely going to be a weak point or sticking point. Depending on the location and your development, you can overcome that sticking point by "strengthening the zone" by focusing work directly in that weak range of motion. Another way to breaking past it is by developing acceleration before that point so more acceleration can be developed to "power through" that sticking point through inertia. 

Granted, this is something you should see during the course of training but gives you a ruler to measure it by. Objective feedback is one of the selling points of VBT. There are likely some practical limitations here like the throughput of information that can be sustained through Bluetooth, but I see this information be utilized more after the fact during set review. This does not need to be a real-time feature, making this still a plausible feature.

Added Value: Tandem Video Recording with Data Overlay for Coaches

I have to admit this is something GymAware already does to the best of my understanding, along with graph overlays. It seems like online coaching with set review is fairly common. Advances in the internet and mobile devices have facilitated the process. I'm all for it, within reason. For coaches that see added value in the velocity data, this helps centralize all the important information by giving the mean velocity of each lift as the lifts are performed. This would be especially helpful for 1RM attempts, RtF sets, and L-V mapping sessions. I highlight those because those three things could throw off the whole accuracy of V-%1RM plots and potentially over/underload future training sessions. Below is an example of video synced with mean power from Dan Baker:

Even on the individual level, this allows the athlete to understand potential causes of velocity inconsistency, such as intervals in which they brace, range of motion contributions to velocity, the magnitude of simple form breakdowns, etc. Unless GymAware has copyrighted this specific tool, it seems easy to implement. This is something people commonly do through two different applications and the feature would merge the process and consolidate the information.

Cut the Fat: Microcycle Management for Coaches

No, I don't think this being able to create and push training plans to athletes is worth a damn. It seems like everyone except for the barebones manufacturers want to provide this. However, it's limiting to the point of being useless. A good example is one manufacturer automatically prompting you to follow the training plan as soon as it starts. Needed a build-up set to figure out what load is appropriate for your working sets? Too bad, that single plate warm-up just counted as one of your 6 working sets. There are plenty of scenarios where this level of inflexible management just performs poorly. Any workout program that's so rigid that it doesn't allow you to take a dump mid-workout to prevent pooping your pants during your squats is a bad workout program - I don't care what it adds to your total.

One example of program creation from Beast

Part of the whole point of auto-regulation is that you're not following a play by play script. These program features attempt to constrain the training process that is meant to be boundless. So I'll make it simple: you don't need to remove this feature, but there are zero reasons to buff it out. If there are recreational users that think it's useful, freeze it's development because it's a waste of time and resources. 

The market is already glutted with program creation and distribution products without VBT. No one's buying the product strictly for this point alone. Recognize it for what it is: fluff. I rate this feature a flat out zero fucks given. Here's a shorthand program that will get me through a session with VBT:

Comp Squat: 6+/2@0.42 m/s, stop @ 0.32 m/s

Close Grip Bench:  @0.54, stop @ 0.30 m/s

Pin Squat: @ 0.6 m/s, stop @ 0.33 m/s

(4x10 follows)

Ab rollout, shoulder external rotation, pull ups

That alone gives me 90% of what I need to know and the other 10% I want isn't supported by any program management tool I've seen.

Air Cast and Mirracast

[Edit 8/8/2017: If it works with Apple, you can cast it. Just make sure you change your screen time out. That said, this actually hasn't been super helpful now that I've taken it for a test drive. I much rather prefer to have some sort of mounting system. Especially when it comes to bench press and I'm staring straight up.]

This is not really a feature that needs direct support. As far as I know, you can do this on both systems, possibly with a little bit of ingenuity. Screen-casting (Air Casting on Apple and Mirracast on Android) solves the simple problem of using the information in real-time. This might seem ridiculous, but it is quite an obstacle to finding a clear way to suspend your iPod in plain view during your squats and bench presses. Granted, a Perchmount makes this easier, but the only way I've gotten this to work with squats has been good ole 2x4" ingenuity. This is probably limited to users that lift in home gyms, but it's something to consider for people that struggle with using real-time feedback to regulate their sets. 

This whole casting idea means less if manufacturers make initial velocity and end velocity prescription more accessible, but there is some additive value of buffing that up with something like delay video casting with metrics overlay on the video. Video demonstrates a simplistic system:

Data Export (Plus Import) and Cloud Based Syncing

This is something some manufacturers already provide. PUSH exports to CSV, which functions the same way as Excel. This seems like a minor thing, but depending on what you're using your device for it can be annoying to manually transcribe information. PUSH is unique that it gives the extraneous details, like time spent concentric/eccentric, force, and other things that aren't available in the user interface. As far as I can tell, Beast doesn't do this. OpenBarbell just made an update that uses your Google login to sync, but as far as I can't tell it's not syncing anywhere where a user can retrieve it and the only viewable data is stored locally - a problem across multiple devices.

Export as shown on PUSH - probably the most underrated feature

The most interesting idea would be removing long-term data analysis from the realm of manufacturers' web portals and allowing hand off to others. There are plenty of platforms that currently do this, like AthleteMonitoring.com and Fusion Sport. Some of these platforms have opened avenues of cross integration to allow automatic syncing (rather than manual inputs) of pertinent athlete monitoring metrics, like heart rate variability. Reactive Training Systems has developed a system that performs according to the metrics Mike T thinks are important, like resting heart rate and subjective questionnaires. It's helpful to note that this service is free to use regardless of whether you work with RTS or not. It does simplify the process. This saves you the trouble of developing your own data collection system and figuring out the analysis yourself. The problem with TRAC is it's developed with RPE in mind. The only other game in town that's powerlifting specific is MyStrengthBook, which is more training analysis than it is athlete monitoring. Regardless, neither currently seem to think of training in VBT terms. If you buffed out your VBT process to include multiple RtF sets alongside referencing velocity to %1RM, you could potentially create a VBT to RIR translator, making TRAC a usable training log.

The truth of the matter is there is no good VBT training tracker for powerlifting. This is to include among the manufacturers of VBT devices. Manufacturers need to abandon the idea of managing their own data when there are plenty of others whose sole attention is managing the training that can do the job better. The first training analysis to take VBT seriously and integrate or import velocity data and provide effective long-term analysis is probably going to a get a lion's share of the VBT consumer's market. The flip-side of that market is it's likely smaller than the RPE market. It would seem to me the easiest way forward would be to exploit the features of MSB/TRAC and translate VBT data into RIR as a proxy for RPE, then release the extensive data under the handle twitter handle Guccifer to satisfy our Russian periodization overlords.

Here's a walkthrough for data export on GymAware's portal:

And finally here's a video demonstrating how you export data on Beast and Open Barbell:

[update: since the original post, Beast and
Open Barbell has added this feature. #TomHanksVBT_Hero]

RESEARCH AVENUES

This isn't nearly as easy. It's easy to find the shortcomings of manufacturer's for current consumer requirements. It's easy to list out the things we don't know. It's hard to list out the things we don't know that we don't know. One of those Donald Rumsfeld known knowns, known unknowns, and unknown unknowns things.

So here are the obvious things we can talk about that we need to pursue on the research side of the house. Most of this is from the interest of strength training and powerlifting, not power development which seems to be better covered in the literature. For the sake of simplicity, this is the short list of things I'm selfishly interested in seeing studied for current needs in powerlifting and strength training.

1) Inter-individual Differences: determine velocity characteristics and differences across heights, limb extremities, anthropometrics, gender, etc

This one seems obvious. Taller folks or people with longer extremities are moving over a longer range of motion. This probably has some influence on their maximum and minimum velocity under load. That part seems easy, but the more complicated part would be examining the effect on sticking points during common movements. 

It'd be interesting to see how well our understanding of the literature holds up for training women and lighter class lifters in terms of velocity. It seems to be internet slapstick to cite that women and lighter lifters have differences in training load and reps at a given %1RM. Given the granular detail VBT provides, it could be helpful to see if we can characterize these training differences in velocity terms (velocity loss, mean velocity, MVT, etc).

2) Intra-Individual Differences: changes in velocity over time from different training modalities

We kind of have a working idea of this through the force-velocity curve, but this doesn't typify the differences in training that any practitioner has seen.

Credit to Haff and Nimphius

Everyone that's worked with a new athlete while running VBT (even if only for observation and not auto-regulation) have typically seen changes in MVT across time, usually corresponding with a change in strength (1RM). I've also seen this difference in speed trained athletes that tend to have higher MVT's than traditionally strength trained athletes. There's probably some interest in finding some middle of the road types of folks, whether that means a type of athlete or a type of training. In that selfish powerlifter way, I wonder how a conjugate method F-V curve compares to other powerlifting training modalities.

Furthermore, a mechanistic view on MVT would be interesting to see. It would seem there are many factors that could contribute to MVT dropping over time, such as changes in form, bar path, and other kinematics, but part of me wonders what the absolute floor to MVT is and whether there is a way we can predict the bottom end of minimum velocity threshold or the absolute minimum that minimum velocity threshold can move. There's probably some energetic or fiber type contribution that would also aid in explaining that, but I feel like that's a far reach and would not significantly impact how I use VBT in training.

3) Characterize particular movements: DEADLIFTS, rows, overhead presses, pull-ups, and variants of the primary lifts

[Edit 8/8/2017 - The Spaniards covered 4 different bench press types: regular bench, bench throws, bench press from pins, and bench throw from pins. They appear to be doing another article on the subject.]

[Edit 8/28/2017 - This has been fleshed out even more with different squat variations, plenty of stuff on pull-ups, and prone rows. The general trend seems to be that when the eccentric and concentric part of the movement is separated, there's increased accuracy and reliability. For many of these things, it's just a matter of the research catching up to what the practitioners know to be true. There have been circumstances where it appears researchers have really challenged our understanding of VBT.]

First of all, we need to recognize that deadlifts quantifiably behave differently. Deadlifts are noticeably absent from the research when it comes to VBT strength training. I get it. You can't publish an article with no real results to show for. It might be more productive to make comparisons across multiple exercises, both in the context of low-moderate intensity for power development and high-intensity for strength development.

Rows and pull-ups (for devices and methods that support body weight movements) are another confounder. When I did measure pull ups, one thing I found was that the velocity floor seemed higher (MVT around 0.42 m/s, far enough within accelerometer performance limits) for rows than it was other exercises. This seemed to be the case for seal rows without resetting to the floor, Yate's rows, and Pendlay rows. Normally I would contribute this to my lack of emphasis on upper back strength (I know I'm not only PL that seemingly negates upper back in favor of comp lifts), but according to folks like Dan Baker, this tends to be the case with his Rugby players that spend a lot of emphasis doing bench pulls.

I can tell you bench, squat, and deadlift general MVTs. I can't tell you overhead press MVT's and only have a rough understanding of velocity behavior across a set. In particular, the first rep and any "broken" reps (short stops at the bottom on successive reps) tend to be lower velocity. I generally don't care about this too much, but it needs to be said since there's some carry over to WL.

A hypothetical graph of %RM-V behaviors

Having a general understanding of how to treat assistance movements would really helpful. For example, if you knew that close grip bench press and Spoto presses were only mildly different from regular bench press, it would be helpful to characterize the magnitude of difference in the same way we generally say bench/deadlift and squat MVT's are 0.15 m/s and 0.30 m/s. It would seem to me that the main difference in the %RM-Velocity plot could be the slope of the line, the intercept, and the MVT. A picture of this would be appropriate and is shown on the right. This is a simplistic explanation, and it's likely certain factors tends to change different parts of the relationship.

This is generally what I find for me and what I've found with a few clients when using VBT as an observational metric, not an auto-regulation metric.

[Edit 8/28/2017 - Actual graphs of variants of the bench press, pin press, bench throw, and bench throw from pins.]

[Edit 9/5/2017: The same graph as above recreated with overlapping trend lines using Desmos online graphing calculator]

4) How rep count schemes and rep tempo modifiers affect concentric velocity

This is somewhat covered in the non-VBT scheme of research. I mentioned in the past the idea of using cluster sets to maintain velocity at high intensity and increase set volume. Myo-reps are another method which acts roughly the same way but is used to increase volume for hypertrophy/work-capacity appropriate loads. The mechanistic approach is helpful, but a good question would be whether this training modality is meaningful.

One interesting development in VBT was a study that focused on a VBT program vs an eccentric VBT program. Spoiler alert, there were no significant differences in 1RM improvements in the squat or bench press when comparing training modality. The Spanish VBT proponents have also played with rep modifiers, finding that imposing a pause between the eccentric and concentric improved reliability (something I have found useful). Anecdotally, I'm wondering if this utility can be expanded to include other tempo schemes. VBT has one added benefit to traditional methods of controlling tempo that it can give instant feedback as to whether the stated goals of the protocol are being met, and thereby what the practical limitations are.

Until we have a clear understanding of these things, we're shooting in the dark or we're going to need other methods to pick up the slack (like RPE).

[Edit 8/28/2017: We're getting a little of that now. This shows rest time equated cluster sets and traditional sets.]

5) Comparison showing the obvious superiority of VBT to that of traditional percent based training and rating of perceived exertion

Not necessary, but if anyone wants to beat down that path they're welcome to it. Different strokes for different folks.

CONCLUSION

Most of the things that manufacturers can do to bring the technology and practice forward are very simple. All of the concepts are not new, and many pre-date many of the VBT devices on the market. Bringing VBT to bear in use in the general public necessitates this process. Simple changes like %1RM-Velocity mapping, Load-Exertion mapping, and others would streamline the process and help athlete management. Many of the features that have been fleshed out apply to those that work with "velocity zones" which are too wide to manage the fine processes of strength training. And when it comes to powerlifting we are working with a narrower range of the velocity spectrum than power athletes. This is not because VBT does not lend itself to strength athletics, but because VBT manufacturers have not made their products nearly as accessible to strength sports.

It is my opinion that manufacturers should focus on how to manage the training session, not try to fill the role of presenting ways coaches (or self-coached individuals) should attempt to manage training across time. Rather than attempting to do two jobs poorly, they should focus on auto-regulation mechanisms internal to the system (via the app) and outsource mesocycle data management to those that have the potential to focus on it better. I've linked to multiple places, but for powerlifting specifically, this is best handled through MyStrengthBook or TRAC. 

The science still has a few questions to answer. Most of these relate to how we understand velocity as a marker of intensity, exertion, and fatigue across more movements and variations of movements. Giving us an understanding how this varies across different individuals or across an individual's development would better help us understand VBT beyond specific practitioners' experiences. 

A Powerlifter’s Guide to Velocity Based Training Pt 1: Device Comparisons

TL;DR

-The purpose of this article is to address the validty and reliability of velocity based training (VBT) measurement devices. 

-Three devices were compared to video analysis: Beast, PUSH, and OpenBarbell V2. Of the three, OpenBarbell seems the most appropriate for powerlifting. 

- “This will be covered largely from a powerlifting standpoint. Also, did I mention this is geared towards powerlifters? I mostly wrote this for people interested in improving their squat, bench press, and deadlift. Athletes that focus on these movements in particular are powerlifters. I wrote this for powerlifters. Powerlifting.” 

-The most important considerations for a VBT device for powerlifters are affordability, reliability at low-end velocity, and support for powerlifting specific movements (primary and secondary lifts) 

-There is nothing that makes a tethered or accelerometer VBT device better than other options without testing across different movements you intend to perform under VBT conditions 

-The limitation of an analysis like this is accuracy or reliability can be improved in some models with no additional hardware changes (adding something to the internals). An update to their respective apps could change how velocity is calculated, rendering this analysis null and void. This was conducted in late January of 2017

[Update 2/18/2017: Added conventional deadlifts. Unfortunately, this addition only includes PUSH and Open Barbell because I no longer have the Beast sensor.]
[Update 8/17/2017: Added some additional commentary. Since this has been released, I've gotten feedback from some manufacturers. As before, this is a snapshot of device performance in early 2017.] 

INTRODUCTION

Velocity Based Training (VBT) is one method of auto-regulating training. It can auto-regulate load on the bar, number of reps within a set, total number of sets, any combination of those three, or any other relevant factor in training. It is beyond the scope of this article to make the case for VBT. It’s hard to make a case for VBT when you haven’t first established that the methods used to gauge velocity are valid and/or accurate. VBT has been a training methodology put forth in power athletes and team sports. It has gotten significantly less attention for strength athletes like powerlifting. Other coaches can more appropriately talk on the matter for strength and conditioning outside of powerlifting, and people like Bryan Mann, Carl Valle, Dan Baker, Eamonn Flannigan, and Mladen Jovanovic already have. On the powerlifting side of the house, the volume of writing and academic work is limited to Louis Simmons of Westside Barbell, Brandon Senn of Kabuki Strength, Mladen Jovanovic of Complementary Training, and I guess you could also argue that Mike Tuscherer of Reactive Training Systems as well – although it’s more appropriate to say Mike uses velocity as a reference point, not a driver of training.

The case for VBT in powerlifting is much the same case as it is for auto-regulated training in powerlifting. Rather than make this tangent over-shadow the assessment of validity and reliability of the sensors, I will direct you to Brandon Senn’s article on the auto-regulation book of methods or wait until I’m able to produce an article that addresses this specifically.

Powerlifting is not a money sport. If you want the best system with the best reliability and accuracy, you should probably do what universities do to test the validity and reliability of velocity based training (VBT) devices. They commonly use VICON 3D analysis systems, or even just run a cross-comparison to another system that has an established track record and vintage prices. Other systems that fit this condition include the T-Force and Tendo linear position transducer. All of these systems are priced out pretty high, so what we’re left with are consumer-grade options, which could arguably be good enough.

Some folks have talked about how linear position transducers, devices that measure displacement and velocity by attaching a lanyard to a barbell is the "gold standard" for velocity based training. There is no gold standard. Saint Verkoshansky, patron saint of the force-velocity curve, did not part the heavens and annoint a clear winner, so let's put that dog to rest already.

Keep in mind, not every device is marketed with the powerlifter in mind. In general, many of the options are aimed at strength and conditioning coaches for power athletes and sports, not for the exclusive use of strength or hypertrophy development. If you just want something to collect silos of data with no contribution to your training plan, there are no particular suggestions for you. If you mean to use it for strength and conditioning, there are many factors to consider – none of which I will cover. Other more qualified evaluators like Carl Valle have covered this in better depth than I could or care too (no offense, I’ll keep following you on Twitter Carl). Powerlifting is the odd-man out here. There is little regard, little attention, and little support in the hardware or software to enable VBT for powerlifting.

Cost is probably the first thing to think about. Unless you’re a sponsored athlete, you’re probably going to consider the more affordable options. Once you’ve determined your budget, it’s essential to consider the coverage of exercises you intend to use it for. This is particularly important because some exercises bottom out at lower velocities than others. It’s also important to consider the direction of the manufacturer. If the manufacturer caters mostly to recreational weight lifters, it probably won’t be that appropriate for you. On the other hand, if it caters to another barbell sport like weightlifters, it might be appropriate for you. And lastly, if it caters to power athletes in team sports, its function and implementation for powerlifting is probably outside of your scope of concern, but might dual purpose well enough. One easy way to see the direction of the company is to look at its change log on its accompanying application. If many of the changes pertain to increasing exercise variety and features that pertain to powerlifting, it might be headed in a direction that will be suitable down the road if it isn’t already appropriate at start up.

And lastly, anyone that says that people should just use BarSense or IronPath: I challenge you to run a 6 week cycle of VBT strength training at intensities of 85-95% with at least 33% of all repetitions performed using VBT feedback. It won’t work, even if the applications work as advertised. The fact that there isn’t an app in the Google Play or Apple app store that utilizes phone internal sensors is beyond my understanding, but no such feasible, low-cost/no-cost option currently exists that operates in real time. And it’s not because VBT is new, because tethered units that have filled a VBT capability like the Tendo have been available for a long time. Anyone recommending this option might as well be recommending a recumbent bike to drive the training of a weightlifter. This is an ignorant argument that doesn’t deserve more than a paragraph of concern.

THE LAY OF THE LAND

This whole section is worth skipping, but here it is… Here’s an obligatory, not-all-inclusive table, because people like tables.

SYSTEM	Tendo	GymAware	Form	Bar Sensei	Beast	PUSH	OpenBarbell
Website	Here	Here	Here	Here	Here	Here	Here
Cost	Not Listed	$2200	$249	$495	$249	$289	$260
Method of Measurement	Tether displacement w/o angle of pull	Tether w/ angle of pull	Accelerometer and barometer, attaches via bar collar	Accelerometer, attaches to the bar	Accelerometer on a barbell or strap	Accelerometer and Gyroscope, attaches to the forearm	Tether w/o angle of pull
Cloud Syncing	No	Yes	Yes	?	Yes	Yes	No
Data Export	Software supported	Yes	?	?	No	Yes	No
Time to Feedback	Immediate	Immediate	?	?	Immediate	If not real time, after set	Immediate
Apparent Purpose	Academic and weightlifting	Anything involving a barbell	Recreational lifters	Power athletes	Recreational lifters	Power athletes and recreational lifters	Anything involving a barbell

So if anyone asks, “Bruh, Y NO GYMAWARE?” look at the price. This blog is NOT monetized and is strictly here for dissemination of VBT ideas in powerlifting. But if someone wants to loan me one, I'll definately add it to the comparisons.

A scatter plot correlation of video velocity and a velocity
measurement device

GRAPH OVERLOAD

First let me explain Bland-Altman plots via scatter-plots.

The X axis is velocity (everything in meters per second) as measured by a Beast sensor. The Y axis is velocity determined using video shot at 60 fps and a free application called Tracker. I’m shilling for Big Physics. You could also use Kinovea, but for the volume of work I was doing alone and the quality of computers I have to work with, this was easier. The dotted line represents how the measurements are correlated to one another. A cursory check of Tracker’s determination of displacement and time appeared to line up with what I could confirm in more rudimentary ways. Many things could affect this as a standard of comparison and it may have been more appropriate to exclude using the program, such as taking the average of all sensors values as the dependent variable. For reasons that I cover later, this was not the most optimal designation of variables.

An example of what a Bland-Altman plot tries to do.... sort of

About the graph: the further from the line, the more they disagree. If the dot is north of the Mason-Dixon line, the video analysis measured the movement at a faster velocity than the Beast sensor did (or that sensor measured it slower than the video). If it’s south of there, then the sensor measured it slower than the video (or vice versa). The slope of the line shows the bias across different quantities. Potential scenarios are that the device could be more accurate as slow velocities and less at fast velocities. In a perfect world, if the graph was scaled at 1:1 (length of grid line matched the height of gridline for the same number of units), this line would form a 45-degree angle. The problem with a scatter plot is putting too many comparisons on it would look too busy, especially in our case if we were measuring different squat type movements (this is measuring back squats, front squats, and pause squats) across three different devices. A Bland-Altman plot helps us visualize it in a greater context by essentially rotating the graph 45 degrees and giving new horizontal and vertical axes showing video analysis velocity and the difference of the sensors relative to the video’s measurement. Something like the picture on the right.

So what does that look like in practice? Like this for a squat: 

Firstly, notice that the horizontal axis (video analysis velocity in the Y direction) is reverse ordered, showing the fastest squats on the left and the slowest on the right (because that reflects intensity/exertion from low intensity/exertion to high intensity/exertion). The vertical axis shows the difference relative to the video, with no difference lying in the center at 0.00 m/s. The colors show different sensors used, and the shapes of each point denote the type of squat. The legend helps you out here: back squat, front squat, and pause squat.

It’s important to note that the squat is likely going to be your longest movement in terms of distance. Since velocity is displacement over time, that means velocity is attenuated by that. For most people, squats will be faster than bench or deadlift. As we decrease velocity (move to the right on the graph), we approach heavier loads. You’ve probably noticed in your own training that you aren’t able to lift your 1 rep max (1RM) as fast as your warm up weight. Velocity reflects this.

You can generally see that OpenBarbell clusters in a generally straight line. At higher velocities, PUSH holds its ground, but it does have a little bit of scatter gun spread going on further down the low end – the part that’s most pertinent to powerlifting.  Beast is roughly near that. But more importantly, this is a comparison of a tethered system against two different accelerometer systems. The supposed superiority of tethered systems is they are more accurate (closer to zero difference). This doesn’t show that. But it does show that it’s reliable.

Accuracy isn’t too important for VBT, but reliability is. Accuracy would reflect how “true” the measurement is to what it’s measuring. So if the 2x6 board is 30 inches, it’s more accurate if it measures it at 32 inches than it would if it measured it at 48 inches. Reliability would be measuring the board 5 times with two different tape measures. One could give a reliable measurement (42, 41, 43, 42, 42) and another could give an unreliable measurement (30, 49, 15, 26, 52). Ideally you want both, but for VBT training purposes reliability is all that’s important. Bad carpenters blame their tools, really bad ones buy twice as much wood. 

Back to the reliability though: if you notice, the differences between sensors and video seem to shrink at slower velocities, or get closer to the 0 m/s difference on the Y axis. Slower reps of the same distance take more time. If you’re dividing the same distance (assuming all your squats are generally the same length of displacement) by increasing times to complete the upward portion of the lift, it slows down and the potential for inaccuracy decreases. Put another way, if it’s reliability is something like plus or minus 5%, smaller quantities (velocity) tend to have smaller difference. But that small difference could be huge. For example, a squat at 0.34 m/s could be tolerable, but a squat at 0.28 m/s could be slower than an individual is able to grind out – like a load above your 1RM that somehow dogmatically followed the trend line and ignored force capacity. It’s probably not helpful to think of VBT as an overly precise tool in prescribing load according to velocity though. Usually, when prescribing a velocity to train at, it’s better to aim for that velocity but accept a range of velocities above and below it. Not huge margins, but if you're aiming for 0.44 m/s, 0.41 or 0.47 m/s might be acceptable. I've seen some templates that seem to use around 5% variance from the target velocity.

The shapes also help us identify if there are movements that are particularly tricky for different systems to measure. In this case, PUSH does not measure front squats as reliably as back squats or pause squats (which is a back squat variant). I’ve always suspected this after loading the bar according to the load-velocity relationship at what should be 70% 1RM and finding myself only able to crank out 5 reps.

If you want to be super technical, here’s the individual points by video velocity and difference for Beast, PUSH, and OpenBarbell. Here’s the correlation between video velocity and Beast, PUSH, and OpenBarbell. If you’re happy with just the coefficients of determination for Beast, Push, and OpenBarbell, they are 0.93, 0.84, and 0.92.

”The coefficient of determination, denoted R² or r² and pronounced "R squared", is a number that indicates the proportion of the variance in the dependent variable that is predictable from the independent variable(s).” The range of coefficients of determination are 0 to 1, with closer to 1 indicating that the regression line perfectly fits the data. 

This does not give the full picture though. To date, I have had zero “dropped reps,” or reps that weren’t detected by OpenBarbell. OpenBarbell gives me so many fewer dropper reps compared to other devices and it's fairly immediate to check before you start whether it's actively recording data. Dropped reps in VBT is what lag is to computer gaming: it’ll kill you ded. The squat is generally more reliable as an exercise because it’s faster and manufacturers know that if you can’t get squats right you’re considered useless because DO SQUATS! PUSH didn’t detect one rep of front squat, as did Beast. Beast also dropped one regular squat. This might not be a big deal on the surface, but if you were trying to determine velocity at 100% 1RM (which you could figure out through AMRAP, arguably) and your sensor dropped one of your 8 reps, that velocity could be lost to the gains goblins of the labyrinth. The opposite could happen too. The sensor could detect 14 reps when you only did 8. Beast calls these “ghost reps” and gives you the ability to choose the ones to cull – which are sometimes obviously wrong and sometimes arguably could be a real measurement. PUSH, on the other hand, only lets you tell it how many reps you did (if you kept count), and determines which measurements to cull without further input (part of their rep detection algorithm).

Again, these methods are as of January, 2017. Manufacturers are always updating their apps. Take much of what I say here as a "snapshot in time" and if you have further questions it's better you check the app reviews or contact me directly. If you think I'm going to review and edit this blog every month, you have a cute relationship with reality.

Sometimes it’s more helpful to manipulate the system and say you completed one or two more reps than you actually performed just so you can see the full range of measurements, but this can get screwy. You could potentially make the system give readouts for reps you didn’t complete. In the case of these charts, dropped reps have been removed from the data set and it biases the measurement to some degree. Keep that in mind throughout this. Reps that these units didn’t detect could possibly be excluded because they are markedly different from adjacent reps and the system self-identifies its own measurement variability. This is the technological equivalent of your dog running into the other room as soon as you come through the front door because they broke the lamp again.

What do I mean by removing dropped reps? How can I remove reps that don’t exist? For example: imagine three dropped reps that were measured by video at 0.3 m/s. If the reps were dropped, that essentially means the difference is -0.3 m/s. If it was a fast rep (which is less meaningful in powerlifting, but here’s an explanation regardless), a dropped rep can mean a difference of -0.75 m/s. This difference is huge. The effect of including them is it misrepresents the bias trend for the rest of the recorded reps, which is of greater interest in the presentation of the data. The unfortunate downside of this is I have to make well-reasoned assumptions as to what are dropped reps vs what are ghost reps.

BANCH, BANCH, BANCH

These measurements do reflect one of my programs, which will be released later. As a result of that exercise selection, there are more data points for bench than there are for the other movements. This is an obvious excuse for why I’m shilling for Big Italy (such innuendo). Exit grapherrhea:

Again, Open Barbell performs fairly reliably and arguably more accurately and reliably. The region of most importance, at 0.60 m/s and below is very tight. Beast seems to handle pin presses very well, which is surprising because Beast usually gets confused when you change direction rapidly (like a barbell bouncing oh-so-softly on safety pins). It almost appears like PUSH has a sinusoidal shaped bias, but it’s hard to tell. This could be a result of how the data is smoothed from its sample rate down to a usable signal. Even though Beast performs better at lower velocity, generally, it also has some scatter at mid-range.

When I say "mid-range," I actually only mean in terms of this graph. In terms of bench, I hardly ever use faster than 0.5 m/s for working weight. This gives a broad picture, but again for powerlifting you should probably focus on the slower stuff. Generally speaking, a powerlifter should have faster reps in higher rep/lower intensity work. A good rule of thumb is to pay special attention to velocities less than 0.6 m/s in the squat, 0.5 m/s in the bench, and 0.4 m/s in the deadlift. If you pull sumo, maybe even slower than that, only paying attention to 0.3 m/s. That's my experience though, YMMV.

Bench press variants surprised me. In a previous article in a blog, I tested multiple PUSH bands at the same time. I tried to set up conditions that tested its reliability, with some possible failure points and some protocols I chose specifically because I was sure they would fail (by using the device incorrectly). At the time, the main validation article PUSH had under its belt utilized curls and multiple individuals at East Tennessee State University under Sato, Beckham, Haff, and Carroll (full author list because Carroll has written more on VBT since then). So I replicated it, broadening the conditions. My “obvious fail” condition was wearing the device in it’s normal configuration on the forearm and comparing that to wearing the device incorrectly at the wrist. The results were fairly consistent. It became obvious that it was measuring angular acceleration and from there determining angular velocity. In the account creation process, one of the inputs you have to give is your weight and height. This was supposed to be a failing condition of my test, but instead I figured (not me actually, my boss did) that it was likely referencing distance and position of the sensor relative in space given proportions of extremities of your height. Further explanation is beyond the scope of the article, but here’s two links to get you started.

My assumption had been that because PUSH likely used angular acceleration, it likely performs better than it should in comparison to other devices in movements that were attenuated by forward/backward movement combined with upward/downward movement. The bar path on the bench press is different from the squat and deadlift in that respect. Greg Nuckols covers that in detail here as does MySquatMechanics, which is my cop out to abandon that tangent. Long story short, I expect PUSH to be better at this than OpenBarbell or Beast. I expected this even more so with reverse grip (RG) bench press since the movement arcs down farther towards the upper stomach or bottom of the sternum. At the low-end of velocity, it tends to do that for RG bench, but it appears scattered in a sinusoidal pattern throughout. Beast performs at a generally predictable bias, but is also scattered at higher velocities. Open Barbell continues to perform well, especially at lower velocities where powerlifters will do much of their important work. Its data generally speaks for itself.

For point of reference, I usually grind out my slowest rep (1RM, no coincidence) at 0.10 m/s. In other studies, 1RM for bench is typically around 0.15 m/s (link to a review article). For powerlifters, Helms and Zordous have found it to be even slower (0.11 IIRC). Most accelerometers systems tend to perform less reliably (anecdotal evidence mostly, but also some implication by manufacturers) at velocities slower than 0.15-0.40 m/s, or in my case ~80% 1RM and above for a bench press. Again, with squats this isn’t nearly as clutch, because 1RM’s are usually around 0.30 m/s (0.24 m/s for powerlifters, again by Zordous and Helms - I think), so we’re not as close to the edge of the variability cliff. Many individual factors will influence your velocity, such as shortening the range of motion because you take a different stance or grip, or you’re American by birth but of Asian height by the grace of God (I can say that, I’m Filipino). For reference to my 1RM velocities (MVT – minimum velocity threshold), I squat at hip width, bench wide, and have a sumo deadlift at 5’5”. My individual experience, thusly, is very challenging for systems that can’t perform as well under 0.40 m/s.

No one wants to tell their best friend they have an ugly baby, but they should hear it from someone that loves them first: PUSH had 4 dropped reps, Beast had 3 dropped reps. As before, OpenBarbell does not drop reps in my experience of over 500 to date drops reps less often and easier to check if it's holding signal before you lift. As before, excluding this data means Beast and PUSH appear more accurate and reliable than they truly are.

Coefficients of determination: Beast=0.81, PUSH=0.92, and OpenBarbell=0.98.

THE GRITTY MESS THAT IS DEADLIFTS

Deadlifts are usually the least forgiving in terms of accelerometer systems dropping reps. I would love to prove that, but I only deadlift twice a week and I only have 48 reps to populate data for PUSH and 35 for Beast. PUSH is notoriously bad at this, and it dropped 7 reps (14.5%). In my n=1 experience, Beast also drops lifts, but that is not substantiated in the current data. I can also tell you that because Beast over-records all movement, you will get significantly more ghost reps in a deadlift if you aren’t setting the bar down quiet enough for planet fitness to approve. This also introduces some bias into the measurement, because even though I’m fairly sure most the measurements included were actually detected and weren’t ghost reps, I’m not absolutely sure. Ghost reps are a huge deal if they register at ~0.30 m/s (which they mostly are) and your deadlifts at 75-80% 1RM only move that fast or slower.

Nonetheless, you’ll see slightly more variation in Beast and PUSH than you will OpenBarbell. Most importantly, you’ll also see this most pronounced at lower velocities. The range of difference nearly doubles. I believe it’s more helpful to see all the individual comparisons separately on the same scale, which I have compiled here.

Given that some accelerometers are measuring angular acceleration, calculating angular velocity, and churning that out into vertical velocity, you could see that something like a deadlift could be challenging. If the unit detects best by change in angle of the unit and the arm is fixed in a downward position throughout the movement, then it doesn't have much to detect. 

This data is very biased by design, but not purposely so. My deadlifts are slow and sumo is usually slower than conventional. As before, less ROM=less velocity. Additionally, I believe the reason PUSH drops reps so often for deadlifts could be is because the sumo deadlift algorithm is fairly new – at least I think they use a different proprietary algorithm for sumo than they do conventional. Since I updated the chart, I think that is the case as 13 of 14 reps of conventional deadlifts recorded. The sumo deadlift algorithm is a year old whereas conventional has been a part of the system since release. Upon early release, the “fix” for rep detection on the deadlift was to complete the pull, drop the weight from hip height, and complete additional reps in the same manner. I think they have since changed this, but there is a possibility that this could also “fix” the sumo deadlift problem. If you’re addicted to data, I guess you should try that out. If you’re just trying to git sum dedlifts, then it might behoove you to find another way to auto-regulate deadlifts.

In general, deadlifts are perplexing for VBT, and I have no definite reason why. Everyone I’ve talked to from Mladen Jovanovic, to Brandon Senn, and other normal VBT device users of Reddit tend to agree with this. 

If you’re really interested in VBT for powerlifting, Mladen Jovanovic and Branden Senn are the best place to start. Bryan Mann, Dan Baker, and others that focus on VBT don’t tend to touch on topics of absolute overlap with powerlifting (bench throws, prone rows, and cleans don't have correlate perfectly to powerlfiting performance), but Mladen and Brandon do cover topics of direct translation to the sport. No offense to Mann or Baker, their insight and lectures have been a great help. 

For many exercises, the first rep of the set is the fastest, and following reps have successive speed decrements if the reps are performed with consistent form and maximum volitional velocity. The widow maker doesn’t do this. Trying to game the movement through starting the movement on the rack at knee height, touch and go reps, pull and reset to the floor reps, performing cluster sets, or pausing at different positions during the lift don’t seem to smooth out the movement’s behavior. This is the ugly baby that VBT proponents don’t like talking about, and opens the floor to many ways of trying to understand how to use the feedback VBT devices provide. It is entirely possible that VBT isn’t appropriate for deadlift autoregulation, or we just haven't figured it out yet. Basing our assessments of performance on subjective measures might be better suited (like RPE) unless we’re talking about final reps left in the tank. This subject deserves an article unto itself.

This phenomenon is reflected in the correlations between video velocity and sensors. Beast has a coefficient of determination of 0.64, PUSH at 0.59, and OpenBarbell at 0.80. Given how well each system generally performed in previous lift classifications, these numbers pale in comparison. Keep in mind, these R²’s are based on the whole range of differences from 40% to 85% 1RM. If you were to increase the sample in velocity ranges typical for powerlifting, there might be completely different conclusions. I decided to include conventional deadlifts after initially publishing this to the interwebs, and I think the differences were only of consequence to PUSH. Unlike PUSH, Beast uses a generalized algorithm for most movement types. Because PUSH dropped so many reps, there was less of a sample size to work with. Knowing that conventional was a long standing detected exercise, I decided to include for clarity's sake, although I realize this comes at a potential loss of comparison to the Beast sensor - again, maybe not since the algorithm is generalized on their data processing. The Beast sensor was not included for conventional deadlifts because by the time I decided to do this I had returned the sensor to the owner.

CONCLUSIONS

The point of this article was to cover the validity and reliability of different VBT devices. Some of these have had their own validation studies and others have studies in the works, but I hope this rudimentary analysis gives you an idea of realistic expectations. It may sound like I’ve been harsh to accelerometer systems, but I would like to bring to your attention that the orientation of this is for powerlifting. Some of these devices weren’t designed to operate within the parameters of powerlifting optimally but do excel in other areas that I have purposely excluded. Tethered units, to include GymAware, aren't super appropriate for 3 axis movement like a bus driver, swings, etc. They're also not super great for movements in which it's not a barbell being manipulated but the body, dumbells, etc. Accelerometer systems tend to circumvent this issue. This evaluation is not meant to be fair, it is meant to gauge narrow, appropriate implementation of VBT devices in powerlifting.

Of the three options, OpenBarbell does appear to be the best suited for powerlifting movements, however it’s application to deadlifts is more limited than it is for benching and squatting. On the surface, it might seem that it may only be appropriate for 66% of powerlifting exercises, but given that many use squats and their variations to build their deadlift I would argue it still has relevance. I would also argue again that this evaluation is a snapshot in time of late January in 2017 and does not speak for how future updates to the hardware or software will augment validity, reliability, or utility of the different VBT devices.

Here’s a table:

If you wish to see more comparisons added to this, I’m willing to evaluate other models as long as it doesn’t involve obligating me to purchase them. In particular, I would like to see Gym Aware added for comparison. I would not like to see the Form Lifting collar added yet as it is a new product and would be unfavorably skewed against an emerging technology which could arguably have valuable technological contribution to VBT. The manufacturer seems to agree with me on the matter in our exchange via email.

It’s worthwhile to point out the limitations of this analysis. Firstly, I’m using questionable video analysis software as the method of comparison across all exercises. On the surface, it does not seem to be a huge concern because the main anomaly in the measurements appears to be deadlifts, but given that other professionals seem to acknowledge the unique nature of deadlifts maybe that is real. However, it does seem odd to me that there are measurements near 1.35 m/s. I have never seen any device measure this high. That velocity is comparable to the peak velocity of weightlifting movements, and I will agree it is suspect. If I had to guess, Tracker is likely overestimating velocity, but given that all movements are from a side profile the bias is likely proportional. This is reflected through the straight trendlines. I’ll cover how I have used Tracker in a following article or video. It would seem to me that it is over-estimating velocity at least at the high end. This discrepancy appears to behave uniformly though, so it may be suitable to use it as a comparison. I could also reanalyze the data to use methods of comparison when there is no known validity, such as comparing the difference of one measurement to the average of all measurements of that given repetition. There are also inherent flaws in that method, especially when you factor in dropped reps. This method could unjustly punish devices that do detect repetitions, which is bass ackwards. Furthermore, this method only works when there are simultaneous measures of the same movement - like a rep being measured by all devices at the same time. The current methods allow for future movements to be added to the comparison graphs subsequent to January, 2017.

Another way to plot the difference would be percent of the difference from the comparison, or the percent difference in the velocity measured by video and the sensor. This could flatten the trendlines, possibly revealing the percentage of velocity is over/underestimates. 

It’s also suitable to consider that one subject isn’t appropriate to generate the data points and a sample of multiple individuals might smooth out variances within a group due to differences in movement proficiency (or lack thereof), limb lengths relative to height, and a host of other factors. I hope the slack that I leave will be picked up by people that are currently evaluating these technologies with funding in universities, such as Dr. Zordous from Florida Atlantic University.

In terms of how to implement a reliable device into a powerlifting program and how to utilize feedback from VBT devices, I will cover these topics in other articles. As a first article, it doesn’t make sense to imply the efficacy of this technology in the sport without first establishing it’s validity and reliability. 

Appendix

I tried to standardize the range of the scale here to improve the clarity of things.