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 char-acteristics 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/cm2), 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 mm3), and tibial density (4 % site) (from 382 +/- 8 to 388 +/- 8 mm3). 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.

Automated summary

This study explored the association between training load and changes in body composition and bone characteristics during a competitive season. The results showed significant changes in lean mass, fat mass, and bone mineral density (BMD) at different phases of the season, indicating the impact of training load on these factors.