Is BMI useful?
For populations yes, for lifters often not: it was built to describe groups, and it has no way of telling muscle from fat.
BMI is a ratio of weight to height squared, and it does its job on large groups, where the average person with a high BMI really is carrying more fat. On one person it is a blunt instrument, which is why a rugby player and a sedentary office worker can land on the same number.
Use it as a rough band rather than a verdict. If your BMI says overweight while your waist is modest and your lifts are decent, the number is describing muscle. If your BMI says healthy while your waist keeps growing, trust the tape.
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Sources
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- Ode, J.J. et al. (2007). Body mass index as a predictor of percent fat in college athletes and nonathletes. Med Sci Sports Exerc 39(3). 439 young adults measured in a BOD POD: BMI caught almost everyone who was actually overfat, but wrongly flagged many athletes, with the best cut-off for male athletes at 27.9 rather than 25.
- Potter, A.W. et al. (2022). Circumference-based predictions of body fat revisited: preliminary results from a US Marine Corps body composition survey. Front Physiol 13. A tape around the waist costs nothing and tells you more about an individual than height and weight alone.