External training load is associated with adaptation in bone and body composition over the course of a season in elite male footballers

This study examined the relationship between training load and changes in body composition and bone characteristics across a competitive season. Twenty senior male professional football players participated in this prospective longitudinal study. Participants underwent dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) scans on four occasions across the study period, resulting in three phases of the season. Phase 1 (Scan 1-Scan 2: 6-weeks: pre-season), Phase 2 (Scan 2-Scan 3: 24-weeks: first part of the season), and Phase 3 (Scan 3-Scan 4: 13-weeks: second part of the season). External training load was quantified using GPS devices. In Phase 1 there was a significant increase (mean ± SE) in lean mass (from 66.0 ± 1.4 to 67.8 ± 1.4 kg) and a significant decrease in fat mass (from 11.5 ± 0.6 to 10.4 ± 0.6 kg). In Phase 2 there were significant increases in whole-body BMD (from 1.41 ± 0.02 to 1.43 ± 0.02 g/cm(2)), leg (from 1563 ± 43 to 1572 ± 43 g) and whole-body BMC (from 3807 ± 100 to 3860 ± 100 g), tibial mass (14 % site) (from 3.72 ± 0.08 to 3.74 ± 0.08 g), tibial strength (SSI(POL)14 % site) (from 2331 ± 78 to 2378 ± 78 mm(3)), and tibial density (4 % site) (from 382 ± 8 to 388 ± 8 mm(3)). In Phase 3, there was a significant decrease in tibial mass (14 % site) (from 3.74 ± 0.08 to 3.72 ± 0.08 g). Bootstrapped (BCa 95 % CI) Pearson correlations showed that in Phase 2 there were significant positive relationships between the increases in leg BMC and total distance (r = 0.44, 0.01–0.80), accelerations (r = 0.45, 0.08–0.75), and decelerations (r = 0.49, 0.07–0.83), and between the increase in tibial strength (SSI(POL)14 % site) and accelerations (r = 0.53, 0.19–0.80). High magnitude dynamic actions, such as accelerations and decelerations were positively correlated with changes in bone characteristics during a professional football season and should be considered by practitioners when prescribing exercise to induce bone adaptation.