Achilles tendon forces and pain during common rehabilitation exercises in male runners with Achilles tendinopathy. A laboratory study

Objectives: To estimate Achilles tendon forces and their relationship with self-reported pain in runners with Achilles tendinopathy (AT) during common rehabilitation exercises. Design: Cross-sectional. Setting: Laboratory. Participants: 24 recreational male runners (45.92 (8.24) years old; 78.20 (8.01) kg; 177.17 (6.69) cm) with symptomatic AT. Main outcome measures: Kinematic and kinetic data were collected to estimate Achilles tendon forces during 12 commonly prescribed exercises. Achilles tendon forces were estimated from biomechanical data and normalised to the participant's bodyweight. The secondary aim was to investigate the relationship between Achilles tendon forces and pain during these exercises. Results: Two exercise clusters were identified based on Achilles tendon forces. Cluster1 included various exercises including double heel raises, single heel raises, and walking (range: 1.10–2.76 BWs). Cluster2 included running, jumping and hopping exercises (range: 5.13–6.35 BWs). Correlation between tendon forces and pain was at best low for each exercise (range: −0.43 - 0.20). Higher force exercises lead to more tendon load for a given amount of pain (R² = 0.7505; y = 0.2367x + 0.6191). Conclusion: This study proposes a hierarchical exercise progression based on Achilles tendon forces to guide treatment of runners with AT. Achilles tendon forces and pain are not correlated in runners with AT.