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

Background: This study aimed to determine differences in the Achilles tendon loading during rehabilitation exercises for Achilles tendinopathy and the ranking of these exercises, based on load, in patients with tendinopathy and controls.

Methods: Sixteen patients with Achilles Tendinopathy (5F & 11 M, 44.1 ± 12.9 yr) and sixteen controls (4F & 12 M, 39.4 ± 15.6 yr) performed rehabilitation exercises while 3D motion and ground reaction forces were measured. Musculoskeletal modeling was used to compute joint kinematics and estimate Achilles tendon load by summing the forces of individual triceps surae muscles. Subsequently, peak Achilles tendon loading, loading impulse, loading rate, loading indexes (a combination of the previous parameters), and joint angles at the time of peak loading were determined and compared between patients and controls.

Findings: Patients with tendinopathy exhibited significantly reduced peak Achilles tendon loading 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). Additionally, during the heel drop exercise, patients with tendinopathy showed reduced ankle dorsiflexion and knee flexion. The ranking of exercises by peak loading or loading index was similar for both groups but varied depending on which loading parameter was used to define Achilles tendon loading.

Interpretation: During the highest load-imposing exercises, patients with tendinopathy 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.