Muscle Isometric Strength and Range of Motion of the Ankle and Hip Analysis in Patients with Unilateral Achilles Tendinopathy: A Comparative Study Between Symptomatic and Asymptomatic Limbs

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Reduced strength and flexibility in the lower limbs are potential risk factors for Achilles tendinopathy (AT). There is a lack of evidence to demonstrate differences in range of motion (ROM) and strength between the affected and unaffected limbs in individuals with unilateral AT. The purpose of this study was to compare the strength and flexibility differences in ankle and hip between the symptomatic and asymptomatic limbs in individuals with unilateral AT. Understanding these differences may contribute to a more nuanced perspective on the biomechanical implications of AT and provide preliminary insights that could inform future research and clinical strategies. We hypothesize that there will be significant differences between the symptomatic and asymptomatic limbs. Methods: A cross-sectional study was conducted using retrospective data collected in a motion analysis laboratory between 2020 and 2024. Forty-four patients with unilateral AT were recruited for this study (8 females, 36 males; mean age and standard deviation: 47.7±10.2 years). Patients with previous lower limb surgeries or any other health condition that could limit test performance were excluded. Bilateral maximal isometric strength assessments were performed using a handheld dynamometer for hip abductors, hip extensors, hip external rotators, ankle dorsiflexors, ankle plantarflexors (with the knee extended and flexed), ankle invertors, and ankle evertors. Additionally, ROM was measured bilaterally for hip internal rotation, weight-bearing ankle dorsiflexion, open kinetic chain ankle dorsiflexion (with knee extended and flexed), ankle plantarflexion, ankle eversion, and ankle inversion. The Shapiro-Wilk test assessed data normality and paired t-tests or Wilcoxon signed-rank tests (P < 0.05) were used to compare symptomatic and asymptomatic limbs. Results: No significant differences were found between the symptomatic and asymptomatic limbs in any of the strength and range of motion tests (Figure 1, p > 0.05). The strength measurements showed similar values for the hip abductors, extensors, and external rotators, as well as the ankle dorsiflexors, plantarflexors, evertors, and invertors. Similarly, range of motion assessments revealed comparable values for hip internal rotation, ankle dorsiflexion (both weight-bearing and open kinetic chain), ankle plantarflexion, and ankle eversion and inversion. The effect sizes ranged from -0.03 to 0.32, thus classified as insignificant or small. The asymmetries in strength ranged from 0.46% to 3.02% (mean = 1.77%) for the tests performed and in ROM they ranged from 0.34% to 11.31% (mean = 3.76%). Conclusion: Individuals with unilateral AT demonstrated symmetry in both ankle and hip isometric maximum strength and ROM between symptomatic and asymptomatic limbs. These findings suggest that static measures of strength and ROM may not fully capture the complex biomechanical profile associated with this condition. In addition, the results show a pattern of symmetry in these parameters, indicating that symptoms do not necessarily correspond to observable interlimb differences in strength or ROM.