The Association between Quantified Training Load and Bone Adaptation

Abstract

PURPOSE: Habitual mechanical loading during pubertal stages has consistently been associated with current and future anabolic effects on bone characteristics. However, the specific aspects of mechanical loading that bring about anabolic effects are yet to be established. The present study investigated the relationship between soccer specific loading patterns and subsequent bone adaptation in youth soccer players. METHODS: 17 elite adolescent soccer players (mean ± SD =age: 16.3±0.5 years; height: 1.79±0.07m; body mass:74.9±6.7 kg) gave informed consent to take part in a study approved by the National Research Ethics Service. Peripheral quantitative computed tomography scans of the tibia of the dominant leg were taken at the beginning of pre-season training and 12-weeks later. Tibial mass (g), trabecular area (mm2), cortical area (mm2) and density (mg·cm2), periosteal circumference (mm) and strength strain index (SSI) (mm3) at the 4, 14, 38 and 66% sites were measured. During the 12 week training period, workload was quantified using a global positioning system (GPS). The following metrics were analysed: session duration (min), total distance covered (m), and high-speed running distance (17.0 km.h-1). Changes in bone characteristics were assessed using paired sample t-tests, and associations between GPS metrics and bone adaptation were assessed using Person’s correlation coefficient. RESULTS: Tibial mass increased by 2.9, 1.2 and 0.7% at the 4, 14 and 38% tibial sites (P < .05). SSI (38%; 2337.1±340.9 compared to 2383.1±317.3, P = .05) and cortical area (38%; 380.9±23.2 mm2 compared to 383.1±30.8 mm2, P = .02) increased following 12-weeks of soccer specific training. Average session duration was positively correlated with increased trabecular area (4%; P=.02, r=0.61) and periosteal circumference (38%; P=.03, r=0.55). Average high-speed running was positively correlated with changes in SSI (14%; P=.05, r=0.51) and cortical density (38%; P=.05, r=0.52). CONCLUSIONS: Soccer specific training increases tibial bone characteristics at the 4, 14 and 38% sites. Moreover, session duration and high-speed running were associated with increased tibial strength, size and density following 12-weeks of soccer specific training. These factors should be considered when recommending exercise for bone health.