Longitudinal Changes in Body Composition Assessed Using DXA and Surface Anthropometry Show Good Agreement in Elite Rugby Union Athletes

Abstract

Rugby union athletes have divergent body composition based on the demands of their on-field playing position and ethnicity. With an established association between physique traits and positional requirements, body composition assessment is routinely undertaken. Surface anthropometry and dual-energy X-ray absorptiometry (DXA) are the most common assessment techniques used, often undertaken synchronously. This study aims to investigate the association between DXA and surface anthropometry when assessing longitudinal changes in fat-free mass (FFM) and fat mass (FM) in rugby union athletes. Thirty-nine elite male rugby union athletes (age: 25.7 ± 3.1 years, stature: 187.6 ± 7.7 cm, and mass: 104.1 ± 12.2 kg) underwent assessment via DXA and surface anthropometry multiple times over three consecutive international seasons. Changes in the lean mass index, an empirical measure to assess proportional variation in FFM, showed large agreement with changes in DXA FFM (r = .54, standard error of the estimate = 1.5%, p < .001); the strength of association was stronger among forwards (r = .63) compared with backs (r = .38). Changes in the sum of seven skinfolds showed very large agreement with changes in DXA FM (r = .73, standard error of the estimate = 5.8%, p < .001), with meaningful differences observed regardless of ethnicity (Whites: r = .75 and Polynesians: r = .62). The lean mass index and sum of seven skinfolds were able to predict the direction of change in FFM and FM 86% and 91% of the time, respectively, when DXA change was >1 kg. Surface anthropometry measures provide a robust indication of the direction of change in FFM and FM, although caution may need to be applied when interpreting magnitude of change, particularly with FM.

Physical and Fitness Characteristics of Elite Professional Rugby Union Players

“…These findings support previous studies which demonstrated forwards as having different body composition [ 11 , 12 , 13 , 15 , 16 ] and anthropometric characteristics than backs, including greater strength and absolute power measures, but slower sprint performance and less aerobic fitness [ 6 , 7 , 10 , 33 ]. The characteristic differences between forwards and backs can be attributed to specific positional demands, in which being larger and stronger can assist forwards with winning line outs, scrumming with more force [ 34 ], gaining and retaining possession of the ball at break downs [ 6 ], and absorbing more collisions through tackles and ball carries [ 4 ].…”

“…Studies within southern [ 6 , 11 , 12 , 13 ] and northern hemisphere [ 7 , 15 ] professional RU players demonstrated similar anthropometric, body composition, and fitness characteristic differences between forwards and backs, as seen in the current study. Interestingly, both forwards and backs within our study demonstrated greater height, body mass, lean mass, and fat mass, but possessed less bone mass and percent body fat compared to professional RU players observed in the northern hemisphere (United Kingdom) [ 15 ].…”

“…Players all possess varying levels of physical characteristics, such as anthropometric (height, body mass, skinfold) and body composition (lean mass, fat mass, bone mass) in order to achieve adequate levels of the desired aforementioned fitness qualities and to meet specific positional demands of the sport [ 7 , 8 , 9 ]. Numerous studies have shown that these fitness [ 5 , 7 , 10 ] and physical characteristics [ 11 , 12 , 13 , 14 , 15 , 16 ] vary greatly depending on the player’s position within the team. In general, forwards have a greater body mass and strength emphasis in order to scrummage with more force, tolerate more collisions and gain and retain possession of the ball [ 11 ].…”

“…Although a range of studies have reported the physical [ 11 , 12 , 13 , 14 , 15 , 16 ] and fitness [ 5 , 7 , 10 ] characteristics of professional RU players and have suggested that body composition with optimal amounts of lean mass and fat mass are important for specific fitness qualities, there is limited literature directly examining the relationships between physical and fitness characteristics within professional RU forwards and backs. Furthermore, physical characteristics in the form of body composition have traditionally been collected using skinfold measurements, which are a practical measure due to their reliability, ease of use, low cost, and portability [ 13 , 19 ]. However, a method that has gained popularity for body composition analysis within professional athletes [ 20 , 21 ] and specifically within professional rugby players [ 11 , 12 , 13 , 14 , 15 , 16 , 19 , 22 , 23 ] is the use of dual-energy X-ray absorptiometry (DXA).…”

“…Furthermore, physical characteristics in the form of body composition have traditionally been collected using skinfold measurements, which are a practical measure due to their reliability, ease of use, low cost, and portability [ 13 , 19 ]. However, a method that has gained popularity for body composition analysis within professional athletes [ 20 , 21 ] and specifically within professional rugby players [ 11 , 12 , 13 , 14 , 15 , 16 , 19 , 22 , 23 ] is the use of dual-energy X-ray absorptiometry (DXA).…”