Addressing muscle–tendon imbalances in adult male athletes with personalized exercise prescription based on tendon strain

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 (εmax) 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, εmax increased significantly in the control group over the 9 months of observation (pCon = 0.010), while there was no systematic change in the intervention group (pInt = 0.575). The model residuals of εmax, as a measure of imbalances in muscle–tendon adaptation, demonstrated a significant reduction over time exclusively in the intervention group (pInt = 0.007). While knee extensor muscle strength increased in both groups by ~ 8% (pCon < 0.001, pInt = 0.064), only the intervention group showed a trend toward increased normalized tendon stiffness (pCon = 0.824, pInt = 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.