Patients with Achilles Tendinopathy use compensation strategies to reduce tendon load during rehabilitation exercises

Abstract Purpose This study aimed to determine differences in the Achilles tendon loading during rehabilitation exercises for Achilles tendinopathy (AT), and the ranking of these exercises in patients with AT and controls. Methods Sixteen patients with AT (5F & 11M, 44.1 ± 12.9yr) and sixteen controls (4F & 12M, 39.4 ± 15.6yr) performed rehabilitation exercises while 3D motion and ground reaction forces were measured. Musculoskeletal modeling was used to compute joint kinematics and triceps surae muscle forces. Individual triceps surae muscle forces were summed to estimate Achilles tendon load. Subsequently, peak Achilles tendon loading, loading impulse, loading rate, loading indexes (combining the different loading parameters), and ankle and knee angles at the time of peak loading were determined. Results Patients with AT have a significantly reduced peak loading of the Achilles tendon compared to controls during the exercises with the highest peak loading: unilateral heel drop with flexed knee (3.66 ± 0.90BW [AT] vs. 4.65 ± 1.10BW [Control], p=0.003, d=0.979) and walking (3.37 ± 0.49BW [AT] vs. 3.68 ± 0.33BW [Control], p=0.044, d=0.742). Furthermore, ankle dorsiflexion and knee flexion were reduced during unilateral heel drop with a flexed knee for the AT group. The ranking of exercises by peak loading or loading index was similar for people with and without AT. However, the ranking of exercises depends on the parameter used to define Achilles tendon loading. Conclusion During the highest load-imposing exercises, patients with AT employ compensatory strategies to reduce the load on their Achilles tendon. Clear instructions and feedback on the patient’s performance are crucial as altered exercise execution influences Achilles tendon loading.