Eccentric vs. Isometric Strengthening for Achilles Tendinopathy: A Randomized Controlled Trial

Abstract

Background: Achilles tendinopathy is a common overuse injury characterized by pain and impaired function. Eccentric exercises (EE) are the cornerstone of treatment, but the efficacy of isometric exercises (ISO) remains unclear. Objective: To compare the effectiveness of EE and ISO in reducing pain and improving function in individuals with mid-portion Achilles tendinopathy. Methods: A randomized controlled trial was conducted with 46 participants (23 per group). Participants aged 18–50 years with ultrasound-confirmed mid-portion Achilles tendinopathy were randomized to either EE (Alfredson protocol) or ISO (45-second high-load isometric holds). Both interventions were supervised and conducted over 12 weeks. Pain intensity (VAS), functional capacity (VISA-A), and tendon elasticity (shear wave elastography) were assessed at baseline, 4, 8, and 12 weeks. Data were analyzed using repeated measures ANOVA, with p<0.05 considered significant. Results: EE led to greater pain reduction (VAS: baseline 6.8 ± 1.2 vs. 12 weeks 2.4 ± 0.9, p<0.01) compared to ISO (baseline 6.9 ± 1.3 vs. 12 weeks 3.8 ± 1.0, p<0.01). VISA-A scores improved significantly in EE (baseline 45.7 ± 8.5 to 74.6 ± 5.4, p<0.01) compared to ISO (46.3 ± 9.1 to 67.9 ± 6.5, p<0.01). No significant differences were found in tendon elasticity (p>0.05). Conclusion: Eccentric exercises demonstrated superior outcomes in reducing pain and improving function compared to isometric exercises in managing mid-portion Achilles tendinopathy. Isometric exercises may be beneficial for early rehabilitation but are less effective overall.