PERFORMANCE BODY COMPOSITION

similar to UWW – it determines body volume based on air displacement (as opposed to water in UWW). Commercially available plethysmography equipment is available under the trade name BOD POD® (Life Measurement, Inc, Concord, CA, USA). The BOD POD consists of two chambers, one in which the individual sits and another located behind the individual. The difference in pressure between the two chambers can be calculated to give a value of the subject’s body volume; in turn, body density and ultimately BF% can be estimated.

As with all methods of composition

assessment, the tester still has to ensure strict pre-test guidelines. There are, however, some distinct advantages associated with the BOD POD over its laboratory-based counterparts, especially UWW. It is relatively quick, with low technical complexity, low user error, and low compliancy expectations of the subject, and its accessibility is good for older people and people with physical disabilities. BOD POD has been reported to underestimate BF% by approximately 3%, but the same author demonstrates that UWW underestimates by a comparable amount.

Generally speaking, the BOD POD

system makes the same assumptions that apply to UWW. Although expense is often the main limitation to BOD POD, the reader should be aware that even when pocket depth is not a concern, recent investigations have suggested that the results may be less valid for lean individuals (below 15% and 18% BF% in males and females, respectively) due to reported reductions in validity within this group.

FIELD METHODS Near-infrared interactance Originally designed for use in agriculture (2), the near-infrared interactance (NIR) method of assessing body fat involves transmitting a beam of precisely measured near-infrared light into the body tissue and subsequently measuring the amount of light that is reflected back. The method is based on the principle that the optical density of tissue is inversely proportional to subcutaneous fat and therefore total fat content (3). The piece of equipment used in research is manufactured by the Futrex corporation, typically the Futrex 5000 (4). The light-emitting probe uses the

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biceps of the dominant arm, as this is considered to be most representative for estimating total body fat. The prediction equation, derived by the manufacturers and performed by the equipment, takes into account the individual’s body weight, height, gender and age. Although researchers have called for the development of equations specific to athletic populations, it appears that this has yet to occur. Generally speaking,

future research needs to focus upon establishing and examining the validity in different populations. Despite being quick and easy to use, one should not overlook the fact that NIR represents the least accurate method reviewed.

Bioelectrical impedance analysis Bioelectrical impedance analysis (BIA) represents one of the most popular methods for assessing body composition. A range of different machines intended for the home user are available. Irrespective of the machine type, the basic premise remains the same: a small electric current is passed through the body and the resistance, or rather the impedance to flow, is measured. Fat acts as an insulator to electric current, whereas lean tissue, containing approximately 73% water, is a conductor. Therefore, the greater the impedance to flow, the higher the individual’s BF%. In terms of measuring the

magnitude of the body’s impedance, BIA represents a valid measure. Unsurprisingly, the determining factor relating to the precision and accuracy of the final value lies in the validity of the prediction equation used – hence, the use of population-specific equations is advised (similar to UWW). With particular reference to BIA, the standardisation of anything that may affect the individual’s hydration status is essential, eg. avoiding alcohol, caffeine and exercise for 24h and fasting overnight before the test commences. Although I do not wish to deter the reader from the use of upper- and lower-body devices commonly seen in high-street shops, it is recommended that BIA devices that display sufficient data in order for the appropriate equation to be applied are chosen. It has been concluded by researchers

BOX 1: ABBREVIATIONS UWW FFM RV

BF%

DEXA FM

NIR BIA

underwater weighing fat-free mass

residual lung volume body fat percentage

Dual X-ray Absorptiometry fat mass

near Infrared Interactance Bioelectrical Impedance Analysis

investigating athletic populations that BIA should not be chosen over the skinfold method when trained individuals are present.

SKINFOLD THICKNESS ASSESSMENT

The skinfold thickness assessment represents the traditional choice for many people. A set of callipers is used to measure the skinfold thickness at a number of anatomical locations around the body, and these values are then substituted into a predictive equation. The principal assumption is that subcutaneous fat provides a consistent indication of total body fat. As with all body-composition methods, the accuracy of the equation is a key component in the final estimation of the individual’s BF%, the most popular being those devised by Jackson and Pollock (5) and Durnin and Womersley (6). Equation issues aside, the most

likely source of error is the technical ability and experience of the tester. The International Society for the Advancement of Kinanthropometry (ISAK) course provides excellent training and accreditation in this field. When performed to the suggested guidelines, identification of the skinfold locations and related landmarks requires the performance of accurate segmental girth and length measures. This process is not as rapid as some sources may suggest; however, although some nutritionists and coaches may consider this a negative aspect when looking at an entire team, it is this author’s opinion that any time penalty is well worth the trade, when the increase in precision and accuracy is taken into account. Although the required equipment is essentially minimal, investment in the most suitable apparatus and its regular maintenance (calliper calibration) is imperative if one expects accuracy

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