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MID-SEASON
DAN HEIL, Ph.D., FACSM
Contributing Editor for the Master Skier
Dan Heil is an avid master skier and triathlete from Bozeman, MT. As Associate Professor of Exercise Physiology at Montana State University, Dan also serves as the director of the Movement Science / Human Performance Lab for testing local master and junior Nordic athletes.
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Eli Enman competes at West Yellowstone.
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How important is it to know your BMI (body mass index) for health and physical performance? If you listen to the plethora of magazine and news stories filling the newsstands and TV news stations, you already know that having high BMI is a strong indicator of risk for a variety of chronic diseases including diabetes, coronary artery disease, certain forms of cancer, as well as all-cause mortality.
Unfortunately, these well-meaning stories have propagated a common misconception that the health risk status of an individual can be easily determined with the calculation of the BMI.
What is BMI?
The BMI is calculated as your body mass (kilograms) by the square of your body height (meters): BMI = (Body mass, kg) / (Body height, m)2. The BMI is considered a very loose correlate of percent body fat (i.e., high BMI should correspond to high body fat).
According to the American College of Sports Medicine, BMI values less than 18.5 is considered “underweight”, 18.5-24.9 are “normal”, 25.0-29.9 are “overweight”, and BMI’s greater than 30.0 are classified as “obese”.
Hundreds of research papers have established a strong association between BMI’s that are too high or too low with chronic disease risk.
The History of BMI
The BMI is an extension of the original height-weight tables created by insurance companies who were first to notice that clients who were very heavy for their height tended to need the most medical payouts and die more frequently from chronic diseases.
It is this association that later led to use of the BMI by researchers in large-scale epidemiological studies. These studies are characterized by a need to track and evaluate physiological data for thousands, or even millions, of people over several years or decades.
In most cases, it simply is not possible to actually measure every variable of interest, or to measure these variables repeatedly over decades. As a substitute, participants fill out extensive questionnaires that include self-reported measures of body height and weight from which BMI is calculated.
In short, BMI is used as a gross indicator of body fatness because there is no other practical measure available to epidemiologists, NOT because it is a superior measure of body fatness or health risk.
In fact, where BMI starts to fall apart is when it is calculated to assess for individuals (as suggested by the news stories) instead of large groups of people (as used by the epidemiologists).
A classic example is the male weight lifter or football player weighing in at 220-240 lbs, 6+ feet in height, and by all visual accounts is a pure athletic specimen. The calculated BMI for this type of person is almost always lands in the “obese” category.
What is BMI Good For?
Calculating your BMI is a good place to start a conversion with a health professional, but not the end of the conversation. Personally, I have found that a visual evaluation of a person wearing athletic clothing is more informative about body fatness than any single objective evaluation technique available.
Athletic clothing leaves nothing to the imagination and those who really are too skinny or too heavy relative to the height and size of their skeletons are going to stand out. However, I cannot personally evaluate every person out there (nor do I want to), so I suggest looking into a full-length mirror at home and objectively evaluating into which of the categories below that you may fall.
I truly believe that the range of “healthy weights” is much broader than is generally accepted by both fitness and health professionals.
Healthy Weight Categories
The Lean Machine - This epitomizes the look of the well-trained endurance athlete who looks fast without even moving.
Most older athletes cannot reasonably achieve this appearance without choosing their parents wisely. So, unless you are less than 40 years of age and possibly training for the Olympics, the Lean Machine look is simply not going to happen.
Athletes who fall into this category without health consequences such as sickness, repeated injuries or the development of eating disorders, should be perfectly healthy with respect to chronic disease risk.
Not Too Big and Not Too Small - Most adults who are habitually active, especially if they train to compete in endurance races, fall into this category.
This is a perfect category for most Nordic skiers because it represents a reasonable balance between the healthy consumption of calories, the expenditure of calories through exercise and the lack of conspicuous excess body fat.
The Chunky Monkey - I see a number of Master athletes, especially Nordic skiers and cyclists, who are packing an extra 5-20 lbs but are fantastic athletes!
Especially after the age of 40, our bodies tend to gain excess fat more easily due to higher work/family stress levels, changes in the balance of circulating hormones (especially testosterone) and a decreased need for calories when performing exercise in combination with no change in eating habits.
Predictably, extra body fat accumulates that even the most diligent exercise addict cannot eliminate. According to BMI standards, these people might be “overweight” and thus at risk for developing chronic diseases.
However, for many older adults, especially those over the age of 60, the “Chunky Monkey” category is actually a healthier place to be than either of the two previous categories.
A number of studies have shown that older adults with higher BMI’s are actually at lower risk for chronic diseases and all-cause mortality than their lighter counterparts. It seems that a higher percent body actually imparts a degree of protection to the older athlete.
Take Home Message for Master Skiers
If you are interested in your personal health risk relative to excess body fatness, don’t rely on a calculation of the BMI. A truly honest and objective evaluation of your appearance in the mirror may not be pleasant, but it is probably a more informative and accurate indicator of health risk than the BMI.
Of course, concerns with having too little or too much body fat should be followed by a consultation with an appropriately trained health care provider.
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