Body composition in sport

Body composition in sport receives much attention from athletes and everyone in their teams, from coaches to dietitians. This is because certain levels of body mass and fat levels are regarded as important for performance and/or aesthetics.

What is body composition?

Generally speaking, body composition refers to the relative amount of different tissues in the body. Most of the time, the main focus is body fat content. However, it is well known that other tissues such as bone and muscle are also important for athletic performance. For example, muscle is essential for generating power (1).

Body composition in sport

Body composition is important in those sports known as weight sensitive. These include:

• Gravitational sports, in which being lighter may confer a performance advantage, e.g. long distance running, ski jumping, high jumping, road cycling, climbing
• Weight class sports, in which athletes compete in a category that has lower and upper weight limits (except for open weight categories), e.g. wrestling, judo, boxing, taekwondo, Olympic weightlifting, lightweight rowing, jockeying, mixed martial arts
• High body mass sports, in which being heavier may confer a performance advantage, e.g. American football, bobsleigh, alpine skiing, snowboarding, rugby, ice hockey, open weight rowing
• Aesthetic sports, which are scored based on physical attributes, e.g. rhythmic and artistic gymnastics, figure skating, diving synchronised swimming, bodybuilding (1, 2)

How to measure body composition

Reference methods

These are the most accurate methods for assessing body composition, hence serving as a reference to determine the reliability of other methods. Unfortunately, these methods are impractical, expensive and/or time-consuming (1).

• Cadaver dissection, which is impractical for obvious reasons, i.e. the subject must be dead (1)
• Multi-component models, such as the 4-component model which uses body density, body water and bone mineral to estimate body fat with a high level of accuracy (1)
• Medical imaging, including MRI and CT scans, which may be useful in the medical setting but are impractical for other purposes. Moreover, CT scans involve a radiation dose which can be detrimental to health (1)

Laboratory methods

As their name implies, these are method conducted in laboratories or medical imaging centres. They include:

• Dual Energy X-Ray Absorptiometry (DXA) which uses a low radiation dose and some assumptions to estimate body composition (1). DXA seems to be accurate for measuring body fat with an error of up to 1% in ethnically diverse athletes and across multiple sports (2). DXA is less susceptible to measurement error due to hydration status (1, 2) and food intake (2) than others methods. However, this method is not very accurate in measuring extremes such as very small, large, lean or muscular athletes (1, 2). DXA measurements should not be done more than 2-4 times per year (1, 2).
• Densitometry which includes underwater weighing and air displacement plethysmography (a.k.a. BodPod). This is a 2-component model which estimates fat mass and fat-free mass by measuring body density. Because fat is less dense than water, it is easy to estimate fat mass. The composition of fat-free mass, however, is dependent on the individual’s total body water and bone mineral density. Reported errors when measuring body fat percentage range from 2 to 8% (1).
• Hydrometry which uses deuterium oxide to measure body water content and subsequently estimate fat mass and fat-free mass. This method assumes certain ranges for water content in fat versus lean tissue, and in the whole body. Hydrometry can produce measurement errors of body fat up to 3% or up to 2% when combined with body density (1).
• Ultrasound which is highly accurate in measuring tissue thickness using ultrasound pulses. There are portable machines that could be used in the field, however standardised protocols and sites have not yet been defined (1).
• 3-D photonic scanning this method is mostly used to depict body shape rather than body composition, therefore its potential use is as a complement to other methods (1).

Field methods

These are methods most used in sports due to their practicality. They include:

• Anthropometry which involves the measurement of height, body mass, skinfolds and girths in standardised body sites (3). These measurements provide information about subcutaneous fat and fat distribution (4). In addition, there are equations than can be used to estimate body fat, of which only a few have been validated in athletic populations (1). This is a popular method because is easy to administer on the go. Also, this method may produce highly variable results, which can be avoided with appropriate training (such as ISAK certification), the use of skinfolds rather than body fat estimates or the use of validated formulas for estimating body fat percentage (2). Skinfolds (but not body mass) are not susceptible to measurement error due to hydration status, dietary intake or exercise prior to testing (3).
• Bioelectrical Impedance Analysis (BIA) is perhaps the best-known method among the general population because it’s used in scales and handheld devices commonly used in gyms. BIA is not highly accurate because it relies on a few assumptions (1), many of the equations used have not been validated for athletic populations (2) and is highly sensitive to hydration status (1, 2).
• Body Mass Index (BMI), which describes the relationship between body mass and height, hence does not give an indication of body fat content (1). BMI guidelines assume that it is associated with body fat content, morbidity and mortality (5). However, this is not the case for lean individuals with large amounts of muscle mass such as athletes (4, 5). Moreover, the relationship between BMI and body fatness varies based on gender and ethnicity (5). Of note, Australian Aboriginal people tend to have a different body fat distribution compared to European Australians, suggesting that the target healthy BMI range for Aboriginal individuals should be lower (6).

A 2013 study reported that DXA and skinfolds were the most commonly used methods for assessing body composition in sport. The choice of method varied from region to region and depending on the competition level (i.e. international versus national/regional) (2).

Factors affecting body composition

Multiple factors can affect the accuracy of body composition methods.

• Hydration status can introduce measurement errors in many methods, including 2C models, BodPod and BIA (3). However, in the study by Meyer et al, only 36% of professionals assessed hydration status before measuring body composition. Hydration was more commonly measured in weight-sensitive sports (2).
• Food intake prior to measurement can greatly increase the error in measurements of both fat mass and fat-free mass. Besides skinfolds, DXA seems to be the method least affected by moderate food intake (less than 500 grams) (3).
• The tester or person performing the measurement should be qualified and certified in the testing method. This is particularly important in surface anthropometry (2, 4).

Therefore, to minimise error, athletes should present for measurement in a fasting state, without having exercised in the past 12-24 hours and euhydrated (i.e. not dehydrated nor over-hydrated) (1, 3, 4).

Why measure body composition?

Measuring body composition on a regular basis can help detect potential harmful dietary practices, overtraining and health issues (4). Moreover, body composition can improve performance, however the ideal body composition for performance varies from athlete to athlete and may not be optimal for health (2).

Too much focus on body mass and body composition can lead to issues such as extreme dieting, disordered eating and eating disorders (1, 2). Given that adipose tissue is an endocrine organ (1), extremely low and high body fat levels are likely detrimental to health.

References

1. Ackland TR, Lohman TG, Sundgot-Borgen J, Maughan RJ, Meyer NL, Stewart AD, et al. Current status of body composition assessment in sport: review and position statement on behalf of the ad hoc research working group on body composition health and performance, under the auspices of the I.O.C. Medical Commission. Sports medicine (Auckland, NZ). 2012/02/07 ed. 2012 Mar 1;42(3):227–49.
2. Meyer NL, Sundgot-Borgen J, Lohman TG, Ackland TR, Stewart AD, Maughan RJ, et al. Body composition for health and performance: a survey of body composition assessment practice carried out by the Ad Hoc Research Working Group on Body Composition, Health and Performance under the auspices of the IOC Medical Commission. Br J Sports Med. 2013 Nov;47(16):1044–53.
3. Kerr A, Slater GJ, Byrne N. Impact of food and fluid intake on technical and biological measurement error in body composition assessment methods in athletes. Br J Nutr. 2017 Feb;117(4):591–601.
4. Going S. Optimizing techniques for determining body composition. Sports Science Exchange. 2006;19(101).
5. Gallagher D, Heymsfield SB, Heo M, Jebb SA, Murgatroyd PR, Sakamoto Y. Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index. Am J Clin Nutr. 2000 Sep;72(3):694–701.
6. Piers LS, Rowley KG, Soares MJ, O’Dea K. Relation of adiposity and body fat distribution to body mass index in Australians of Aboriginal and European ancestry. European Journal of Clinical Nutrition. 2003 Aug 1;57(8):956–63.

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