Many athletes have goals to increase muscle mass, decrease fat mass, or both. Often the term “lean body mass” is used when athletes express interest in gaining muscle. While muscle mass and lean body mass are used interchangeably, lean body mass does not only include muscle mass, but also bones, ligaments, tendons, and internal organs. In fact, there is even a small amount of essential fat in the marrow of bones and internal organs that gets included in lean body mass.
There are many reasons athletes seek body composition changes, and appropriate nutrition recommendations for body composition changes are addressed in Chapter 8. Collecting information on body composition as part of the assessment allows for appropriate goal setting and consequent nutrition recommendations. The focus for athletes is typically increasing their muscle mass and decreasing fat mass, and assessing body composition can determine if an athlete’s goal for change is realistic. For example, if an athlete already has very low body fat and their goal is to compete in a weight class that is 15 pounds lower than their current weight, it is likely they would have to lose some amount of fat-free mass (muscle) in order to achieve this goal. This may not be desirable. Also, monitoring this information over time (reassessing body composition using the same methodology) allows athletes and practitioners to see if changes are being made and can determine if interventions targeting body composition alterations are successful.
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There are various methods for assessing body composition, and practitioners should be aware of the advantages and disadvantages of each. The only way to directly assess body composition is through dissection of the cadaver. Obviously this is not a desirable approach! All other methods are indirect and therefore have certain limitations. Understanding the principles and assumptions underlying the various methods is crucial for accurate interpretation and application. Determining body composition requires identification of different body compartments. Basic, two-compartment models measure fat mass and fat-free mass. Models analyzing additional components such as three-compartment models (measuring fat, bone, and lean mass), or even four-compartment models (measuring bone, adipose, muscle, and other tissues) increase the accuracy of the results. Yet, increasing the number of components measured can greatly increase the cost and reliance upon advanced technology and equipment.
Some assessment tools are more precise than others, and practitioners have to consider variables including what is accessible to them and the athlete, time commitment, cost, availability of published normative data, and training of technician, among other considerations. Keep in mind that all forms of assessment have a margin of error, and this error range needs to be included in interpretation of results.
Skinfold measurements. Collecting skinfold measurements can be a quick and inexpensive way to assess body composition. This method requires a skilled trainer and calibrated skinfold tools, and when these criteria are met, a skinfold assessment on an athlete can be fairly reliable. The practitioner uses calipers to measure folds of skin on specified areas of the body and these values can estimate fat mass and fat-free mass. The skinfold values can be entered into an equation that calculates a percentage of body fat. Since each equation has only been validated on specific reference populations, there is limited applicability to all athletes. There are several types of calipers and procedures that are used in the field, but the protocol developed by “The International Society of Advancement of Kinanthropometry” (ISAK) is considered the gold standard. This method requires implementation by a certified practitioner following a standardized procedure that ensures accurate measurements and minimizes error. Because even a 1 cm deviation in a site measurement can produce significantly different results, using standardized techniques with precise definitions of measurement sites is essential (Ackland et al. 2012). Additionally, when using a prediction equation, the same calipers and technique should be used each time measurements are taken to ensure reliability.
Of note is that ultrasound technology can also be used to measure skinfold. This technique is becoming more common since it decreases trainer error and thus is considered more accurate. However, access to ultrasound technology to be used in this capacity may be limiting, as well as the cost of the technology, depending upon the resources that are available to the athlete.