Effects of an exercise program on calf muscle characteristics in patients with Achilles tendinopathy

Objective in participants with Achilles tendinopathy. Additionally, it explored the relationships between muscle adaptations and functional outcomes. Design: Prospective observational study. Setting: Laboratory-based assessment. Participants: Thirty-five participants with Achilles tendinopathy completed a 16-week exercise program. Main outcome measures Muscle EI of the medial (MG) and lateral gastrocnemius (LG) and soleus (SOL) was assessed using ImageJ. B-mode ultrasound was used to measure MG(CSA), LG(CSA), and SOL thickness at baseline and post-intervention. Functional outcomes included single-leg countermovement jump (CMJ), drop CMJ, and heel-rise (HR) endurance tests. Results MG(EI) and LG(EI) significantly decreased on both symptomatic sides (p < 0.05, d = 0.5-0.8). MG(CSA) and LG(CSA) increased (p < 0.05, d = 0.3), while SOLEI and SOL thickness did not change (p > 0.05). Heel-rise work improved (p < 0.05, d = 0.4), but jump heights did not. Regression analysis showed that age, BMI, and muscle changes did not predict improvements in HR work (Adjusted R-2 = 0.11, p > 0.05). Conclusions: The exercise program reduced muscle EI and increased hypertrophy but did not significantly improve calf endurance. Further research should explore how muscle adaptations affect function in Achilles tendinopathy rehabilitation.