Toolbox: Body Fat Testing
One of the unfortunate societal pressures we all face to differing degrees is the demand to be thin and beautiful. In cycling, this manifests itself as an obsession with minimizing body fat at all costs. Just how important is it for cyclists to be as lean as possible, and what are the tests we can use to measure body fatness?
Body weight and body image is one of the trickiest topics to broach in sports, whether as an athlete, teammate, coach, or parent. Some sports, such as gymnastics and figure skating, impose huge aesthetic demands on its female athletes to be as small and light as possible, leading to a high prevalence of eating disorders. Other sports, such as rowing, boxing, and wrestling, impose its own unwritten demands of losing as much weight as possible immediately prior to “weigh in” in order to compete within a certain weight category, leading to dangerous dehydration practices.
Cycling is certainly not immune from its own weight biases, as demonstrated by the cycling press’s fetish with Ullrich’s weight over the years. And being confirmed Euro-geeks, we look at ourselves in the mirror and think how much faster we could be if we only lost that extra few pounds.
How Low Can You Go?
Within reason, it is certainly true that, all things being equal, a lower body fat percentage can definitely improve your cycling. This is especially true when climbing, where the fight against gravity and slower speeds means that the primary determinant of performance becomes power output : body weight ratio. This is in contrast to flat-land performance, where the overwhelming importance of aerodynamics means that the primary determinant is power output : frontal surface area ratio. This is why lightweight climbers who may not have massive ABSOLUTE power outputs can climb fast, but are disadvantaged on the flats compared to big and muscular rouleurs.
Of course, in both cases, excess body fat is not generating power and is essentially “dead” weight. But there is a limit to a good thing. We all have a certain level of essential body fat, approximately 3-5% for males and 12-15% for females, which is required for tasks such as physical and thermal insulation, fuel reserve, and nerve conduction. Going near or below these levels result in reduced recovery and impaired immune system response.
Females face the additional threat of irregular or stopped menses. Once a point of pride among endurance athletes, we have now come to recognize the dangers of the Female Athlete Triad and the strong interactions between: 1) eating disorders, 2) menstrual irregularities, and 3) long-term increase in risk of osteoporosis. So the moral of the story for both males and females is to walk that fine balance between a healthy approach and concern about nutrition weight without crossing over the line of obsession.
Measuring Body Fatness
What are the primary tools we can use to track our body weight or fatness? They range from the simple to the expensive and exotic. The key for me, as discussed previously, is consistency and reliability.
• Weighing The simplest way to track weight, of course, is with a scale. This can range from your inexpensive bathroom scale to the one in my lab that costs nearly $4K. The key is to be consistent in when and how you weigh yourself. Ideally, this is first thing in the morning after your bathroom trip. Also, DO NOT weigh yourself every day or worry about 1 kg either way. You’re looking for long-term patterns over weeks or even months.
• Weight and Body Fatness It’s important to note that weight and body fatness are NOT closely related! As muscle is denser than adipose tissue, you can end up decreasing your body fat and have increased muscle mass (e.g., through consistent resistance training), yet end up at the same weight. Of course, the opposite can be the case, especially as one ages and activity levels may decrease.
• Hydrostatic Weighing Underwater weighing is often considered the gold standard for body fatness measurement, because it can directly and fairly accurately calculate body density (fat is less dense than muscle, so a fatter person weighs less underwater than a leaner person of the same weight). This body density is then converted to body fatness. The main limitation is that only a few specialized facilities, usually university exercise physiology labs, will be able to perform them. So of course that’s an expensive option, leading to the two following alternatives.
• Skinfold The most popular alternative to hydrostatic weighing is skinfold measurement, using a caliper to measure the thickness of the fat layer directly under your skin. This can be used to estimate body density, from which the same equations are used to calculate body fatness. Seems easy and cheaper, but beware that technique is absolutely critical (garbage in, garbage out) and harder than it seems. Therefore, make sure the tester is credibly certified, and ideally use the same one each time. Other caveats include natural changes in skin thickness with age, and also that the equations used to estimate density and fatness are population specific and many not apply to you very well. One popular way among scientist to get around the problems with equations based on assumptions is simply to report the individual skinfold values or else the sum of all of the skinfolds.
• Bioelectrical Impedance You may have seen fancy weigh scales in stores or your gym that claims to tell you your body fat too. How they work may be a “shock” to you – a tiny current is sent from one part of the scale, through your body, then to another part of the scale. As fat is an electrical insulator, changes in body fatness changes the speed at which the current is conducted through your body. A huge series of assumptions are used to convert from current conductivity to body fatness, so the accuracy of these units tend to be pretty shaky. However, we’re more interested in reliability, which is pretty good as long as you use the same unit each time.
There are lots of other big and expensive ways to measure body composition, but they aren’t overly practical and you’ll only find them in very high-priced labs or research hospitals. Again, the main thing to consider with body weight or fatness measurement is reliability or consistency (how repeatable is the measurement) rather than the accuracy or validity (does it actually give you the “correct” value).
We will talk much more about nutrition in future Toolboxes but, as with anything in life, it is essential to keep a healthy perspective on nutrition, body weight, and body image.
Stephen Cheung is an Associate Professor of Kinesiology at Dalhousie University in Halifax, Nova Scotia, Canada, with a research specialization in the effects of thermal stress on physiology and performance. He can be reached for comments at [email protected].