Why You Shouldn’t Rely on the BMI

Odds are that at some point in your life you’ve been classified based on the Body Mass Index (BMI) or have used the BMI to classify clients. Although the BMI is a quick and easy way to get a general idea of where somebody’s body fat is, it’s far from accurate. As an NCCPT personal trainer you want to be accurate and avoid these BMI problems.

Developed in 1832 by a Belgian astronomer, statistician, mathematician, and sociologist named Lambert Adolphe Jacques Quetelet, the BMI was intended for his own use in his studies that were unrelated to a person’s obesity. Many, many years later, insurance companies began to notice a correlation between weight and health issues and began to use it in their preliminaries. It has since become a more commonly used tool despite its flaws.

Among its flaws, the BMI does not take into consideration a person’s waist size, lean muscle mass (which, as you know, adds weight just like fat does), and other critical factors.

Although the BMI can be useful for getting a quick idea of where a client’s body fat generally is when they start and as they work with you, it is not a tool that should be relied on for accurate measurements of progress. In fact, progress shouldn’t always be tracked by weight alone.

When working with clients, be sure to implement a strict tracking system, but don’t put too much emphasis on the numbers on the scale. Instead, focus on their overall progress and results; how far they’ve come, the changes that can be seen, how much better they feel, and increased performance like added stamina, agility, ability to lift heavier weights, and all other benefits of working toward a better physical self.