Three-compartment body composition changes in professional rugby union players over one competitive season: a team and individualised approach

We investigated 3-compartment body composition across one competitive season in professional male rugby union players using dual-energy X-ray absorptiometry (GE iDXA). Thirty five 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 DXA scan at pre-season (August), mid-season (January) and end-season (May), enabling quantification of body mass, total and regional fat mass, lean mass, percentage tissue fat mass (%TFM) and bone mineral content (BMC). Both team and individual changes were evaluated, and for the latter, least significant change (LSC) was derived from precision data and applied as per International Society for Clinical Densitometry guidelines. Mean body mass remained stable throughout the season (p>0.05), but total fat mass and %TFM increased from pre to end-season, and mid to end-season (p<0.05). There were also statistically significant increases in total-body BMC across the season (P<0.05). In backs, there was a loss of lean mass between mid and end-season (P<0.01). 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 end-season. Twelve players exhibited no change. Strategies to improve the maintenance of pre-season lean/ fat ratios across the season for professional rugby union players might be beneficial to performance and health, and thus require exploration. We recommend that future studies include an individualised approach to DXA body composition monitoring and this can be achieved through application of derived LSC.