Three-Compartment Body Composition Changes in Professional Rugby Union Players Over One Competitive Season : A Team and Individualized Approach

The purpose of this study was to investigate longitudinal body composition of professional rugby union players over one competitive season. Given the potential for variability in changes, and as the first to do so, we conducted individual analysis in addition to analysis of group means. Thirty-five professional rugby union players from one English Premiership team (forwards: n = 20, age: 25.5 ± 4.7 years; backs: n = 15, age: 26.1 ± 4.5 years) received one total-body dual-energy X-ray absorptiometry (DXA) scan at preseason (August), midseason (January) and endseason (May), enabling quantification of body mass, total and regional fat mass, lean mass, percentage tissue fat mass (%TFM) and bone mineral content (BMC). Individual analysis was conducted by applying least significant change (LSC), derived from our previously published precision data and in accordance with International Society for Clinical Densitometry (ISCD) guidelines. Mean body mass remained stable throughout the season (p > 0.05), but total fat mass and %TFM increased from pre to endseason, and mid to endseason (p < 0.05). There were also statistically significant increases in total-body BMC across the season (p < 0.05). In both groups, there was a loss of lean mass between mid and endseason (p < 0.018). Individual evaluation using LSC and Bland-Altman analysis revealed a meaningful loss of lean mass in 17 players and a gain of fat mass in 21 players from pre to endseason. Twelve players had no change and there were no differences by playing position. There were individual gains or no net changes in BMC across the season for 10 and 24 players, respectively. This study highlights the advantages of an individualised approach to DXA body composition monitoring and this can be achieved through application of derived LSC.