Getting into and staying in shape is hard, there’s no doubt about it, but many of us often mistake difficulty for complexity. Yes, if you’re an elite level athlete or bodybuilder, elements of your diet and schedule can get complicated, but for the rest of us just working to avoid needing a new, looser pair of pants, the mechanics of fitness are simple: burn more calories than you take in, and you’ll lose weight. Lift more weight and you’ll gain strength. Do more repetitions and you’ll gain endurance.

At a glance, those statements seem like oversimplifications, but for many Americans that have spent the better part of their lives on the couch, embracing those broad stroke realities will create a noticeable difference. Then, as your familiarity and comfort with a fitness regimen grows, you can add more complex elements to suit — tracking your protein intake, experimenting with the number of sets and reps you prefer, and so forth. Of course, much of the internet is intent on convincing you that it can’t be that easy. You need to pay a trainer, buy a diet book, eat ground up herbs, subscribe to a meal service, purchase the right stretch pants and get your master’s in Kinesiology if you ever hope to lose that spare tire!

There’s a simple explanation for the folks that want you to believe those are the requirements to lead a healthy life: they make their living by selling them to you. Don’t get me wrong, there are good supplements, good books, good trainers and great stretch pants — if that’s the sort of stuff you’re into — but none of them are make or break elements of your endeavor to become fitter. The fitness industry is booming thanks to these sorts of misconceptions, and while some were indeed born out of intentional marketing gimmicks, others are based on simple misunderstandings and still more root from outdated beliefs that we’ve come to accept as fact. In previous editions of Old Man Fitness, we’ve addressed a number of these sorts of myths and misconceptions (you can find those articles here and here) and this week we’re getting right back at it — because there are no shortage of things most of us still get wrong about getting right with ourselves.

Body Mass Index (BMI) is bullshit.

If you’ve ever looked at the scale in your doctor’s office with a bit of trepidation, it’s probably because you knew he or she would about to give you a hard time about your BMI, or Body Mass Index. BMI is painfully simple to calculate because it uses only two criteria: your height and weight. The problem with assessing your overall health using only two very basic measurements is that it fails to take innumerable other variables into account that may play a direct role in your health — like bone density or muscle mass.

I’m six feet tall and weigh around 250 pounds. According to my BMI, that qualifies me as not just grossly overweight, but clinically obese.

Fat ass.

It really should come as no surprise that your Body Mass Index is a poor measurement of one’s health, seeing as the man who developed it (who, notably was a mathematician and not a doctor) even said so. According to Lambert Adolphe Jacques Quetelet, the Belgian who conjured up the BMI index nearly two centuries ago, the BMI calculation was intended to provide broad population averages for government projects, not to assess one’s personal health.

Nowadays, we cling to the BMI index for two reasons: it’s simple, and it allows insurance companies to charge lots of people more money. For example, my life insurance premiums went up by quite a bit after they put me on a scale and ruled me “obese.”