Change is the Key Metric

web3Evaluating fat loss and muscle gain can be tricky and prone to human error. Ask three trainers to calculate data with a tape measure or calipers, and you’ll get three different results. When done right and presented correctly however, positive metrics can be very motivating. The secret to success is precision.

Club owners and gym members are bombarded with tools that claim to accurately measure body composition and other health and fitness metrics. Some methods are straightforward, while others are esoteric and difficult to understand. To make matters worse, the results of many body fat analysis devices and methods don’t agree with each other. That makes it tough to trust the number a machine spits out. It begs the question, is there a truly universal way to measure body fat that’s 100 percent accurate?

No. Unless you want your client to sacrifice their life so you can remove all the fat from their body and then weigh it, there is no way to measure body fat with 100 percent accuracy. But there is a way to measure body fat precisely. What’s the difference?

We like to use accuracy and precision synonymously. But in reality, they are very different. Think of accuracy as the “target” and precision as “repeatability.” I’m a big baseball fan, so I’m going to use an example of a pitcher. An accurate but imprecise baseball pitcher is wild, but his average location is around the center of the strike zone. Unfortunately, umpires don’t call strikes based on the average position of multiple pitches. A precise, but very inaccurate pitcher, always misses the strike zone, but always misses in the same place. The latter is consistent and reliable. All things being equal, a coach or scout is always going to favor the reliable pitcher, even if he always misses the strike zone. The reason is that a small mechanical change will make the reliable pitcher both accurate and precise. In the case of the accurate but imprecise pitcher, much more could be going wrong and be difficult to correct.

When judging fitness and health metrics, we must always favor precision when evaluating a tool because we are interested most in trends. The initial number doesn’t really matter so long as it meets general expectations. What matters most is the ability to precisely measure changes with respect to that initial assessment. Having a repeatable baseline is more important than having the true answer, because it allows us to trust that something is truly changing — change is the key metric.

When evaluating body composition analyzers, ideally look for a device or method that has ballpark accuracy (pardon the pun), but is highly precise. Ideally, some level of accuracy is quite important. But more importantly, run a few samples with the same subject and measure the dispersion or spread in the data. If it’s more than 1 percent, look elsewhere.


Raj Sareen is a physicist turned entrepreneur and the CEO of Styku, known for its popular MYBODEE system, a 3D body scanning system for measurements and body composition. For more information, contact


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