Friday, December 07, 2007
How Not to Measure Fitness
There are all kinds of ways to measure how physcially fit you might me. I'm here to talk about two that aren't good methods:
1) The bathroom scale.
2) The body mass index (BMI).
For those of you who don't know, BMI does a ratio between your height and weight, and assigns a number to this ratio. If it this number is under 18, you are considered too thin, and if it is above 30, too fat. If your BMI is, say, 35, you are morbidly obese.
A lot of doctors use the BMI without bothering to notice that it has a major flaw.
Doctors, when I was in the field as PA twenty-five years ago, were woefully unaware of the nature of fitness. We had a patient come in for routine physical once. He had a resting pulse rate of 48, and the doctor who saw him was all set to run a shitload of tests and maybe stick him into the hospital -- sinus bradycardia (slow heartbeat) can be dangerous.
Thing was, I was training to run in a marthon at the time, reading Runner's World Magazine, and The Physician and Sports Medicine, and the patient looked fit, so I asked him if he was a runner.
Yep. Six miles a day.
I then explained to the doctor that aerobically-fit jocks developed the heart just as any other muscle will if you work it, and that at 48 beats, this guy was pumping blood the way an average person would at 72 beats per minute. The slow rate was not a problem, but a measure showing much fitter than average his heart was, aerobically-speaking.
The doctor had never heard of this.
BMI's big flaw is that it does not speak to percentages of muscle and body fat. When Ahnahl the Governator won the Mr. Olympia Contest as the most muscular man in the world, with a bodyfat less than five percent, he was, according to his BMI, "morbidly obese ..."
Weight varies for a lot of reasons. Thursdays, I usually fast. Black coffee, lots of water, now and then a glass of wine in the evening, but no food.
This Thursday when I got up, just for fun, I stepped onto the bathroom scale: 206 pounds, which is close to what I usually weigh.
Thursday night, after not eating all day, but drinking a couple liters of water and three cups of coffee, it was 202 pounds.
When I got up this morning, 200 pounds even.
By noon, three cups of coffee, but no food, it was 198.5 pounds.
I was no fitter at noon than I was at nine a.m., given that all I did was sit in a chair and type.
There are ways to measure bodyfat, aerobic fitness, flexibility, and strength. Use those. Not the bathroom scale or the BMI. You can go down two pants sizes and gain weight -- muscle weighs more than fat because it is denser. You jock out, get tighter, lose inches, but can weigh more.
Your mirror tells the truth ... if you can accept what you see ...