When it comes to body fat, don't believe what your eyes tell you

Credit: Doug Pensinger/Allsport
We can easily describe the look of professional road cyclists in a few words: thin, trim, hungry, and gaunt.

In fact, competitive road cyclists are among the leanest individuals in the world. Studies have shown male road cyclists to have as little as three to five percent of their total body weight as fat. And while women must carry more than that (probably due to fat's role in reproduction), female road cyclists may show body fat levels as low as seven to ten percent.

Despite such exceptions, the generally accepted minimum values, termed "essential fat," are three percent for males and twelve percent for females.

Below these levels, growth, athletic performance and physiological functions may be impaired. Compare these low percentages of fat to those considered "ideal" or "recommended" for the normally active person. Exercise physiologists recommend 15 to 17 percent for males and about 18 to 23 for females.

Percentages of fat above 20 to 25 percent for men and 30 to 35 percent for women impose an extra burden on the heart and may compromise good health.

Optimum cycling performance, however, calls for much lower levels of fat. In general, male elite road cyclists measure between three and eleven percent fat, while females range from twelve to 18 percent.

While science has yet to determine to just what degree changes in body weight affect cycling performances, clearly, the fatter you get, the slower you get. Excess body fat raises the work level required to move the body at a given speed or over a given distance without adding to the body's ability to generate energy.

Given this relationship, then, how can one determine one's own body-fat percentage? Well, you might expect to be able to tell how fat an individual is simply by looking at the person. In many cases, though, you'd be wrong.

For example, someone who appears thin but does no exercise may actually be carrying enough fat, (relative to lean or nonfat tissue) to be considered "obese." But a stocky, muscular person may look fat, yet prove as lean as a competitive athlete. With body composition, as with many other areas of life, appearances can deceive.

Relying on body weight can be just as misleading, since fluctuations in weight reflect not only changes in body fat, but also degrees of hydration and gains or losses in muscle tissue.

If appearances, scales and standardized weight charts offer little value in estimating body fat, what works better? The most widely accepted methods are skinfold-thickness measurements and underwater weighing. The first uses specially-designed calipers to measure skinfold thicknesses at selected sites on the body.

From these measurements, trained technicians can extrapolate body-fat percentages. With underwater weighing, also called hydrostatic weighing, the subject is weighed while completely immersed in a large tank of water. Since fat floats and lean tissue sinks, this process shows just how "dense" a person is. Although underwater weighing is more accurate, in most cases you can get very close with skinfold calipers, which are easier, more widely available and less expensive.

Certainly, most cyclists, whether already considering a weight-loss program or not, could benefit from body composition analysis. The following case history illustrates just how widely body-fat percentages can vary, as well as how certain changes in diet and activity levels can influence body composition.

A 40-year-old male cyclist who, concerned about his appearance, felt he should begin a weight-loss program. In addition to cycling, this man lifted weights and played racquetball on a regular basis. At 5'4" and 160 pounds he looked solid, though far from lean, and he measured at least ten to 14 pounds overweight according to standard height/weight tables.

Yet, underwater weighing revealed that his body was only 12 percent fat, or 19 pounds of fat compared to 141 of lean tissue. Thus, the man's "high" weight was primarily a function of the large muscle mass he'd built up through weight training. The body composition analysis showed him that a weight-loss program was unnecessary.

Online training diary. Use our Active trainer to record your mileage and vital stats.

Shop for cycling gear and much more at the Active Sports Mecca

Find and register for a mountain bike tour or race in your area!

Got a question for Dr. Burke? Send it here.

Discuss This Article