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Mechanical Properties of the Achilles Tendon Aponeurosis Are Altered in Athletes With Achilles Tendinopathy

Background: Achilles tendinopathy is a considerable problem for active people. The degenerative processes associated with tendinopathy may be associated with changes in the inherent mechanical properties of the musculotendinous unit. Purpose: The purpose of this study was to compare Achilles tendon–aponeurosis strain between male athletes with and without Achilles tendinopathy. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Fifteen healthy men (age, 35 ± 9 years; height, 1.78 ± 0.05 m; mass, 79 ± 11 kg) and 14 men with midportion Achilles tendinopathy (age, 40 ± 8 years; height, 1.77 ± 0.06 m; mass, 80 ± 9 kg) who were all running over 20 km per week participated in the study. Each participant was tested in a single session that involved maximal isometric plantar flexion efforts being performed on a calf-raise apparatus while synchronous real-time ultrasonography of the triceps surae aponeurosis was recorded. Achilles tendon–aponeurosis strain (%) was calculated by dividing tendon displacement during plantar flexion by resting tendon length (intrarater reliability: intraclass correlation coefficient = .92). Results: Participants in the Achilles tendinopathy group (5.2% ± 2.6%) had significantly (P = .039) higher Achilles tendon–aponeurosis strain compared with the control group (3.4% ± 1.8%). In contrast, there were no significant between-group differences for maximal isometric plantar flexion force. Conclusion: Achilles tendon–aponeurosis strain is higher in male athletes with tendinopathy than those without. The results of this study provide a rationale for current clinical approaches to management of Achilles tendinopathy, whereby repetitive mechanical loading may impart a positive benefit through reduced compliance of the musculotendinous unit.