Body fat testing: Why and how

Body composition assessment is an important part of the athlete assessment process and forms the basis for nutritional interventions. In this short article I explain some of the methods available for body composition analysis and the pros / cons for these methods.

As a nutritionist, I see body composition testing is an essential part of athlete monitoring, especially if their body fat levels have an impact on their sport. As well as providing a starting point, regular monitoring of body composition provides feedback to the effectiveness of my nutrition interventions and whether or not adjustments are required. Whilst motorsport athletes aren’t required to ‘weigh in’, as per combat sports or horse racing, excessive body fat and/or weight could be seen as detrimental to performance by lowering the power to weight ratio of the machine, particularly when teams spend large sums of money on lightweight components.

Whilst several methods of body composition assessment are available,  skin-fold tests provide the easiest and, arguably, the most consistent method due to the portability of the equipment (a pair of skin fold callipers and measuring tape) and the standardisation of the testing procedure. Whether in the race paddock, the lab or visiting an athlete’s home, the skin-fold test is always the same, providing consistent results and instant feedback. Another benefit of skin-fold tests is that a lot of athletes can be tested in a short amount of time.

One of the limitations of the skin-fold test is that the results are presented as a ‘sum of eight’ score, that is, each measurement is given in millimetres, with the total from eight sites providing the final value. This score can then be converted into an estimate of body-fat percentage using an equation, but several equations exist and each one will provide a different result. This makes translating the results to athletes difficult as the majority like to hear their score as a percentage. As a general rule, I like to see my athletes around a score of 60mm, which translates to a body fat percentage of approximately 9 – 12% depending on which equation you use.

Another option is Dual-energy X-ray absorptiometry (DEXA), which requires the use of an expensive scanner. Originally designed to measure bone density, DEXA scans also produce an estimate of body fat and lean tissue mass. It’s a simple test that takes approximately 5 minutes, with the athlete simply lying down on the scanner bed. Whilst DEXA scanning might seem an attractive option, research has shown that the fat and lean mass results can be influenced by body water, so the reliability of the results remains questionable. However, obtaining an estimate of an athlete’s bone mass can form the basis for nutritional interventions, particularly in a high-risk sport such as motocross and speedway, where having healthy, strong bones is important due to the likelihood of injuries.

Summary

Skin-fold tests provide the easiest and most consistent results of body composition assessment. The International Society for the Advancement of Kinanthropometry (ISAK) is recognised around the world as the ‘gold standard’ in skin-fold testing and practitioners are required to complete a multiple-day course to become certified. In the past, I’ve had an athlete’s body composition tested whilst he was in Australia, by simply arranging for another ISAK qualified trainer to complete the assessment. In motorsport, I’ve found a skin-fold score of 60mm or below to be ideal, as this is an achievable and sustainable target for most athletes. For athletes who aren’t naturally lean, maintaining anything lower than this level of body fat can be difficult, compromise training due to lack of energy and potentially increase the risk of illness.

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