A Better Way to Evaluate Body Composition
Combine two popular methods and move closer to your goalMarch 16, 2011
Photo by skamille
With the holidays behind us and a new season setting in, consider thinking about body composition as one of the primary areas for improvement in this New Year. Athletes typically think about body composition in a very one-dimensional way. Most don’t get too far beyond considering only their body weight and/or the percentage of their body weight that comes from fat. Outlined below is a more effective, sport-specific approach to body composition that uses traditional metrics in a more synergistic way.
The two primary metrics to consider are Body Fat Percentage (BF%), and Body Mass Index (BMI). There is limited sport-specific value in using these metrics separately. When used in conjunction with one another, however, they can provide insight into sport-related performance limiters, which go well beyond the impacts of only body weight on race speed and/or vanity.
When BF% and BMI are combined, they yield a powerful tool for evaluating potential athletic limiters and moving beyond them.
The first step in carrying out a detailed evaluation of body composition is to take an accurate measurement of body fat. There is no need to go crazy in getting an exact number in this context—a number plus or minus 1.5 percent will be appropriate. By working with a dietitian and/or coach, athletes should target an approximate race day BF% as well. Assuming this number is as low as the athlete should safely be based on age and gender, a goal body weight should then be determined. (A goal that operates under the assumption that this number can be reached through manipulating the diet).
Let’s look at an example: If an athlete currently weighs 160 pounds, with a 12 percent BF% and an eight percent goal BF%, we can assume that the athlete will lose four percent of his or her body weight through manipulating the diet. To determine this athlete’s goal race day body weight, we calculate 4% of 160, which is about six pounds. Assuming that this athlete does not lose a significant amount of muscle during the weight loss phase, they can expect to race at about 154 pounds, and with eight percent body fat. We call this is the athlete’s Lean Adjusted Body Weight.
This process is a powerful tool in helping determine an athlete’s optimal race weight, as well as the attendant impacts on performance. Assuming that this goal BF% has been properly determined and that there has not been a significant loss of strength due to a loss of lean muscle mass, each pound of lost body weight roughly equates to a three second per pound per mile improvement in running pace and about three seconds per pound for every four miles on the bike. With this in mind, once the above athlete has shed these six pounds of body fat, an improvement of about 18 seconds per four miles and 18 seconds per mile can be expected on each of the bike and the run paces.
Integrating BMI into this evaluation along with BF% adds a great deal of value to the process. It adds the ability to consider the athlete’s muscle mass content. Consider the idea that every sport has it’s own optimal BMI, where strength does not act as a performance limiter and is not in excess of what is needed. If an athlete’s lean adjusted body weight yields a BMI below the sport’s requirement, then there is a good chance that strength will act against them. In this case, strength should be a primary target of the athlete’s season plan, along with the appropriate dietary changes to support muscle mass development.
To calculate lean BMI, multiply lean adjusted body weight by 703, and then divide this number by the square of the athlete’s height in inches. If this lean adjusted BMI is much above that required for the selected sport, then it is likely that the extra muscle mass being carried around is not needed for optimal performance and will actually slow the athlete down. In my experience for triathlon, the optimal lean adjusted BMI is about 20 for females, and 21 for males. Remember, this metric only has value when combined with BF%, to create a lean adjusted body weight for the BMI calculation.
For example, if BMI is calculated for an athlete with significant body fat without first being adjusted for lean body weight, it will result in an artificially high number. This is due to significant body fat with no correlation to the sport-specific strength evaluation. It should be noted that a sport like rowing would have a higher optimal BMI because of the significant strength component required.
In summary, evaluating sport-specific body composition for an athlete should proceed as follows:
1) Determine the athlete’s current BF% and, with the assistance of a good coach or dietitian, determine a target race day BF%;
2) Adjust body weight assuming that this goal will be reached;
3) Calculate BMI with this lean adjusted body weight;
4) Evaluate this BMI versus the aforementioned sport-specific ideals (Triathlon: 20 Females, 21 Males);
5) If above or below these ideals, the athlete’s training/nutrition program should be manipulated with the goal of working towards these ideals.
How to go about reaching these goals (in terms of muscle mass gain/loss), is beyond the scope of this piece, however, as it can become quite complicated. Regardless, the process outlined above sheds light on how an athlete may be able to squeeze additional speed out of an already sound training program, and further understand where their specific limiters may lie. When BF% and BMI are combined, they yield a powerful tool for evaluating potential athletic limiters and moving beyond them.
Jesse Kropelnicki is an elite/pro level triathlon coach who founded QT2 Systems, LLC; a leading provider of personal triathlon and run coaching, as well as TheCoreDiet.com a leading provider of sports nutrition. He coaches professional athletes Caitlin Snow, Dede Griesbauer, Ethan Brown, and Tim Snow, among others. You can track his other coaching ideas on his blog at www.kropelnicki.com.