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Power metrics in the weightroom are flawed, but you should still use them

I am a big fan of using power metrics derived from velocity tracking technology.

Power provides a simple, easy to understand metric that drives intent and motivation in training.

However, many training educators and S&C coaches do not share my enthusiasm for power metrics. They point to the flawed and invalid methods used for calculating power, calling it a “fluff metric” not suitable for precise training.

The below snippet from Bryan Mann (inventor of the velocity zones) explains his rationale.

These critiques are for the most part accurate. Power calculations have limitations, especially in the world of VBT. But despite this, I still use power as a metric in my training and coaching plenty and believe power has immense value as a training tool - especially for coaches and athletes looking to optimize their training.

In this post, we’ll take a dive into the what and why behind power metrics, including:

  • Key terminology
  • How power is calculated (and the issues with different methods)
  • Why power is considered a "fluff" metric
  • The advantages power metrics provide
  • How to program power training effectively

Key Terminology

First, so that we are all on the same page, let's define some key terms around velocity based training and power metrics:

  • Velocity - The speed of the barbell during the concentric (upward) movement. Usually the mean velocity across the entire rep.
  • Mean velocity - The average speed of the barbell across the entire concentric (upward) movement.
  • Peak velocity - The fastest single moment of speed of the barbell during the concentric (upward) movement. Usually this happens right near the top (lockout) of the rep.
  • Load - The external resistance or weight being moved. Typically the barbell weight.
  • Power - The rate of doing work. Calculated by factoring in load lifted, gravity and the velocity of the movement. Measured in Watts.
  • Mean power - The average power of the barbell across the entire concentric (upward) movement.
  • Peak power - The fastest single moment of power of the barbell during the concentric (upward) movement. When using a VBT app, this happens at the same moment as peak velocity.
  • Maximum Power - The highest number of watts produced across any weight for an exercise, usually around 40-70% of 1RM.
  • Relative Power - The number of watts generated when divided by your bodyweight. This gives a score as Watts per kilogram or W/kg.

How Is Power Calculated?

There are a number of different ways that power can be measured and calculated, but fundamentally all power calculations are based on some variation of the equation:

Power = Load x Velocity x Gravity

load and gravity are the easy parts of the equation to collect, but in order to measure power correctly, you need to use a bar velocity tracker, such as the Metric VBT app. There are differences  based on technology and whether you are looking at mean or peak power, but in the world of velocity based training most of the power tracking debate is around:

  • Whether to include bodyweight (system load) in the calculation
  • How do you measure velocity and,
  • where do we measure velocity from

Does body weight affect power?

One debate in power calculation is whether to include system weight - the bodyweight of the athlete - within the power calculation.

Typically in standard training exercises, power is calculated from the external load being lifted alone, however this makes it trickier to have fair competition based on relative power, skewing results towards smaller athletes. This also creates an incomplete picture of how much power the athlete is generating on on jumps where the majority of the resistance is provided by their body mass.

So should you include this extra weight in the power calculation? Probably. Although it gets a bit tricky as jumps might be moving 100% of the athletes bodyweight, while on cleans or squats only 75% of the athletes body mass is being moved (the other 25% is doing the moving).

Metric VBT does not include system load in it’s power calculations, as we opted for a simpler first power metrics, however adding a relative power score and enabling this sytem load tracking is likely to be something we explore in the future as an advanced feature.

How do you measure velocity at the gym?

Velocity is the key variable for determining power in resistance training. But where and how you measure it during an exercise can play a big role in the accuracy of this data.

The most practical way to measure velocity is for lifters and coaches to use a velocity based training VBT device or app to measure the speed that a barbell moves during an exercise. For example, the Metric VBT app uses the computer vision plus the camera on your iPhone to track the barbell in HD video and at 60 frames per second, delivering accurate and reliable bar speed and power data.

Another option is to use force plates, which can be great for specific physical tests, but due to cost and logistics they do not scale as a regular tracking tool for training if you wish to track power every week on multiple exercises across many athletes during training.

Where to measure lifting velocity from

Measuring velocity at the system centre of mass provides the most scientifically valid representation of the athlete's power expression. This is called system velocity.

System velocity may offer some improvements in scientific rigour, but for substantially increased complexity. To measure this system velocity with validity requires motion capture technology, and sophisticated calculations to combine barbell motion, body motion and torque around multiple joints simultaneously. For training purposes, measuring velocity and therefore power barbell velocity provides a simple, effective means of calculating power.

Regardless of where you fall on these three power measurement theories, the real key is practicality and consistency. Using the same formula and measurement approach over time allows us to achieve the goal of all of this, which is to be improving and tracking an athlete's power generating capacity.

Why Is power considered a "Fluff" metric?

Unlike pure velocity data, power is a composite metric - made up of load, velocity, gravity, and potentially bodyweight. This means that if power changes, a scientist might not be able to directly pinpoint what caused that power metric to change, making for a frustrating research conclusion.

In training we don't really care* what made an athlete get better, just as long as they are getting better, coaches and athletes will take progress however it comes. And because power is so vital for so many of the things that make better athletes better (jumping, throwing, sprinting etc) directly measuring and watching this power number go up is a huge win.

*I mean we do care, being able to repeat a program, isolate program variable etc matters a heap. But we don't care in the same way that a scientist deeply cares about showing why a thing worked. This is where great coaching blends research, logic, technology, art and experience to do what we do.

The advantages of power training metrics

The context baked into power metrics that makes them frustrating for scientists is what makes them so practical and useful for a coach - providing us with a single metric that provides instant insights into an athletes lifting without the need for deeper analysis, correlation, regression or any of that other technical work that frankly most athletes don't get all that excited about.

Power metrics are a trade-off in scientific purity for simplicity, explainability and ease of use. Athletes want to be more powerful, athletes understand power and athletes enjoy things they understand. Power is easy to understand.

Power metrics provide immense value to athletes and coaches by being:

  • Customized - Power profiles are unique to each athlete and exercise
  • Motivating - Athletes can chase new power PBs every session
  • Autoregulating - Power dictates load, catching fatigue and preventing overwork, especially useful in-season
  • Readable - Power is a single metric that is easy to explain to athletes quickly. Power is an easy to understand score that drives intent and intensity.

Power training programming methods

You can find more detailed applications of power training and programming methods in part 2 (coming soon), but here are some examples of effective power programming ideas that leverage the use of power metrics in your training (check out the links for more details):

Metric VBT is an app that measures velocity and power in your training, it's free to download and use, with advanced features available with a Pro subscription.

Download Metric on iOS here →

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References and resources

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