Body Composition Monitoring and Sports Performance

Posted on 21/02/2012 by Ste Smith There have been 0 comments

Athletic performance is, to a large degree, dependent on the athlete's ability to sustain power (both anaerobically and aerobically) and to overcome resistance, or drag. Both of these factors are interrelated with the athlete's body composition.

In the minds of athletes, there is an inherent conflict between overcoming the resistance, or drag, associated with sport and having enough energy to sustain power output over the entire course of a competition or training session.

An athlete who is carrying excess weight may be more prone to injury when performing difficult skills than the athlete with a more optimal body composition. However, when athletes attempt to achieve an optimal body composition, their methods are often counterproductive. Diets and excessive training often result in such a severe energy deficit that, although total weight may be reduced, the constituents of weight also change, commonly with a lower muscle mass and a relatively higher fat mass.

Know your body

First, however, it’s worthwhile to appropriately assess if you even need to lose weight. This is where evaluating things like body composition (using more than just a mirror!), body mass index, regular menstrual cycles (for women), normal testosterone levels (for men) and regular summer or winter seasonal weight variations all play a role in the assessment. It makes no sense for training or health to force an unnatural bodyweight.

It is worthwhile remembering your weight is primarily made up of water, muscle, fat and bone. Understanding your natural baseline for body water, muscle and body fat is a good way of assessing how your body responds to training, injury recovery and setting goals for an ideal pre-race physique. Focus should be to have a long-term mentality or mind-set.

This is where the latest Body Composition Monitors can really make a difference. Using the Advanced bio-electrical impedance technology (BIA), the scale measures body fat, body water, muscle and gives key indicators such as basal metabolic rate, visceral (abdominal) fat and bone mass. The Tanita BC1000 Body Composition Monitor can even wirelessly transmit all measurements to a Garmin Fitness Watch (FR60, FR60LTD, FR70, 310XT, 610 and Forerunner 910) and Garmin Connect allowing training sessions to be assessed directly with body composition changes.


Usually during the preparation training the volume and intensity begins low. You might be doing less miles and speed in the beginning with a focus on base building or rebuilding. Throughout preparation, training intensity and volume will gradually increase.

Weight loss comes in to play more during the beginning stage of this cycle. The more miles and intensity you add to training, the less you want to focus on weight loss and more on your muscle/body fat balance. A diet lacking particularly enough carbohydrates and protein during critical phases of training can contribute to risk of injury, heighten fatigue, and compromise good training. Keeping track of your Daily Calorie Intake or Basal Metabolic Rate is a good way to stay in tune with your body’s changing nutritional needs. Again, the clever Tanita Body Composition Monitor provides this information in seconds.

Finding the optimal muscle/fat ratio and hydration level during periods of intense training can make a big difference to your race time.

Sports Scientist have calculated that for every 1% of body mass loss, primarily as body fat, there could be a 1% increase in running speed. A brief example: if an average 80kg male, 4 hour marathon runner, was to lose 5kg (about 6% loss) this could mean an improvement of about 15 minutes – 3:44:50 (around 6%). Of course this is based on excess body mass and any weight loss and care should be taken with not to reduce to excessive levels.

Pre-race and race day

Training intensity increases during the weeks leading up to a race. You might be doing faster speed sessions with longer rest. This seems to also be the time anxiety often rises over being close enough to a perceived ideal race body composition. Last-minute weight loss effort is not uncommon. The thing is, even if you’re not increasing miles, energy requirements are high. This is a critical time in training where weight loss efforts can actually impair performance especially if the weight loss is coming from lean muscle mass instead of body fat.

As race day closes in, intensity might still be up but volume goes down in effort to rest up for race day. For longer races this may even involve carbohydrate loading to maximise glycogen stores. Losing weight during this time in training, again, can negatively affect performance. During the pre-race period and race day, focus should be on fueling well, carefully monitoring body water levels and preparing for competition. This includes after the actual race. Be sure to refuel soon after competition to facilitate the recovery process.

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