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

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.

Personalized tendon loading reduces muscle-tendon imbalances in male adolescent elite athletes.

An imbalanced adaptation of muscle strength and tendon stiffness in response to training may increase tendon strain (i.e., the mechanical demand on the tendon) and consequently tendon injury risk. This study investigated if personalized tendon loading inducing tendon strain within the effective range for adaptation (4.5%-6.5%) can reduce musculotendinous imbalances in male adolescent handball athletes (15-16 years). At four measurement time points during a competitive season, we assessed knee extensor muscle strength and patellar tendon mechanical properties using dynamometry and ultrasonography and estimated the tendon's structural integrity with a peak spatial frequency (PSF) analysis of proximal tendon ultrasound scans. A control group (n = 13) followed their usual training routine, an intervention group (n = 13) integrated tendon exercises into their training (3x/week for ~31 weeks) with a personalized intensity corresponding to an average of ~6.2% tendon strain. We found a significant time by group interaction (p < 0.005) for knee extensor muscle strength and normalized patellar tendon stiffness with significant increases over time only in the intervention group (p < 0.001). There were no group differences or time-dependent changes in patellar tendon strain during maximum voluntary contractions or PSF. At the individual level, the intervention group demonstrated lower fluctuations of maximum patellar tendon strain during the season (p = 0.005) and a descriptively lower frequency of athletes with high-level tendon strain (≥9%). The findings suggest that the personalized tendon loading program reduced muscle-tendon imbalances in male adolescent athletes, which may provide new opportunities for tendon injury prevention.

Effect of sex on muscle-tendon imbalances and tendon micromorphology in adolescent athletes-A longitudinal consideration.

Imbalances between muscle strength and tendon stiffness may cause high-level tendon strain during maximum effort muscle contractions and lead to tendon structural impairments and an increased risk for tendinopathy in adolescent athletes. However, it remains unclear whether the development of musculotendinous imbalances is influenced by sex. At four measurement time points during a competitive season, we measured quadriceps femoris muscle strength and patellar tendon mechanical properties in 15 female (14.3 ± 0.7 years) and 13 male (16.0 ± 0.6 years) elite handball players of similar maturity using dynamometry and ultrasonography. To estimate the tendon's structural integrity, the peak spatial frequency (PSF) of proximal tendon ultrasound scans was determined. Females demonstrated significantly lower muscle strength (p < 0.001) and patellar tendon stiffness (p < 0.001) than males with no significant changes over time (p > 0.05). Tendon strain during isometric maximum voluntary contractions and PSF neither differed between sexes nor changed significantly over time (p > 0.05). We found lower fluctuations in muscle strength (p < 0.001) in females during the season but no differences in the fluctuations of tendon strain, stiffness, and PSF (p > 0.05). Descriptively, there was a similar frequency (~40%) of athletes with high-level tendon strain (>9%) in both sexes. These findings suggest that the lower strength capacity of female athletes is paralleled by lower tendon stiffness. Thereby, muscle-tendon imbalances occur to a similar extent in both sexes leading to increased strain levels during the season, which indicates the need for specific tendon training.