The ACTN3 gene and differences between playing positions in bone mineral content, fat mass and lean tissue mass in the arms, legs and trunk of Rugby Union football players

Aim: The function of the present study was to identify differences between individual playing positions in bone mineral content, fat mass, and lean tissue mass, in the arms, trunk and legs of young adult Rugby Union football players who carried the ACTN3 gene. Subjects and methods: A cross-sectional case control study was carried out using a candidate gene approach (n=55). Individuals belonged to a homogeneous group of players relative to age, gender, ability, and ethnicity. Players were allocated to their preferred playing position. These were the front row (n=14), second and back rows (n=16), scrum and outside-half (n=11), and centres, wings and fullbacks (n=14). A 5 ml sample of saliva was obtained from each player and specimens stored at 4oC until buccal cell DNA extraction was carried out. Height was measured to the nearest 0.1 cm and body mass to the closest 0.1 kg. Dual-energy X-ray absorptiometry was measured using a Hologic QDR Discovery fan beam model. Statistical analyses were undertaken using ANOVA, ANCOVA and MANOVA. Results: The study sample comprised 22% RR, 60% RX, and 18% XX genotypes of the ACTN3 gene respectively. Players in the second and back rows were significantly taller than other positions. Body mass differences, were significantly greater in forwards than backs. There were non-significant differences between positions in adjusted bone mineral content or adjusted lean tissue mass. Adjusted fat mass reflected differences between left and right arms, but not left and right legs. Conclusion: At a developmental level of performance, an understanding and practical application of the structural, physiological and body composition characteristics of individual players, will facilitate personal and team accomplishment, efficiency of training and conditioning, and nurture the potential of young adult players. Keywords: Playing position; ACTN3 gene; Body compositio