Abstract
PURPOSE: Imbalances of muscle strength and tendon stiffness can increase the operating strain of tendons and risk of injury. Here, we used a new approach to identify muscle-tendon imbalances and personalize exercise prescription based on tendon strain during maximum voluntary contractions (ε(max)) to mitigate musculotendinous imbalances in male adult volleyball athletes. METHODS: Four times over a season, we measured knee extensor strength and patellar tendon mechanical properties using dynamometry and ultrasonography. Tendon micromorphology was evaluated through an ultrasound peak spatial frequency (PSF) analysis. While a control group (n = 12) continued their regular training, an intervention group (n = 10) performed exercises (3 × /week) with personalized loads to elicit tendon strains that promote tendon adaptation (i.e., 4.5-6.5%). RESULTS: Based on a linear mixed model, ε(max) increased significantly in the control group over the 9 months of observation (p(Con) = 0.010), while there was no systematic change in the intervention group (p(Int) = 0.575). The model residuals of ε(max), as a measure of imbalances in muscle-tendon adaptation, demonstrated a significant reduction over time exclusively in the intervention group (p(Int) = 0.007). While knee extensor muscle strength increased in both groups by ~ 8% (p(Con) < 0.001, p(Int) = 0.064), only the intervention group showed a trend toward increased normalized tendon stiffness (p(Con) = 0.824, p(Int) = 0.051). PSF values did not change significantly in either group (p > 0.05). CONCLUSION: These results suggest that personalized exercise prescription can reduce muscle-tendon imbalances in athletes and could provide new opportunities for tendon injury prevention.