Football-specific training characteristics and changes in bone characteristics in male academy football players.

Quantifying load during training may progress our understanding of skeletal adaptation during team-sports, such as football. This study aimed to assess external training load and changes in bone characteristics and body composition over 14 weeks of preseason in academy footballers (n = 15). Whole body dual-energy X-ray absorptiometry scans were performed at baseline and 14 weeks to assess bone characteristics and body composition. Global positioning systems (GPS) and changes in strength measures were monitored over 14 weeks to measure external load during competition and training. Bootstrapped paired-sample t tests showed that academy footballers increased leg bone mineral content (BMC) (p = 0.008), total BMC (p = 0.022) and lean mass (p = 0.030) following preseason. No other changes were shown in bone or body composition characteristics. Bootstrapped Pearson correlations showed positive associations between total BMC change and high metabolic load distance (total amount of high-speed running coupled with the total distance of accelerations and decelerations, r = 0.36), accelerations (r = 0.42), and decelerations (r = 0.39). Change in lean mass was negatively correlated to high-speed running ( r = -0.49) and very high-speed running distance (r = -0.45). There were no associations between changes in muscular strength and changes in bone or body composition. GPS-derived external load measurements of acceleration and deceleration in academy footballers were associated with a positive response in BMC. These adaptive responses may have been in response to external load measurements quantifiable by GPS. Further studies associating GPS-derived metrics with skeletal outcomes during football are required to fully elucidate how football-specific training characteristics may influence bone structural properties.