With the twofold stimulus of mechanical loading and maturation acting on the muscle-tendon unit, adolescent athletes might be at increased risk to develop imbalances of muscle strength and tendon mechanical properties. This longitudinal study aims to provide detailed information on how athletic training affects the time-course of muscle-tendon adaptation during adolescence. In twelve adolescent elite athletes and eight similar-aged controls knee extensor muscle strength and patellar tendon mechanical properties were measured over one year in three-month intervals. A linear mixed effects model was used to analyze time-depended changes and the residuals of the model to quantify fluctuations over time. The cosine similarity (CS) served as a measure of uniformity of the relative changes of tendon force and stiffness. Muscle strength and tendon stiffness increased significantly in both groups (p<0.01). However, the fluctuations of muscle strength were greater (A: 17±7 Nm, C: 6±2 Nm, p<0.05) and the uniformity of changes of tendon force and stiffness was lower in athletes (CS A: -0.02±0.5, C:0.5±0.4, p<0.05). Further, athletes demonstrated greater maximum tendon strain (A: 7.6±1.7%, C: 5.5±0.9%, p<0.05) and strain fluctuations (A: 0.9±0.4, C: 0.3±0.1, p<0.05). We conclude that athletic training in adolescence affects the uniformity of muscle and tendon adaptation, which increases the demand on the tendon with potential implications for tendon injury.
- Copyright © 2016, Journal of Applied Physiology