Abstract
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 SOL(EI) 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.