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Effect of habitual running on human Achilles tendon load-deformation properties and cross-sectional area

Team Danmark Test Center/Sports Medicine Research Unit, Bispebjerg Hospital, 2400 Copenhagen, Denmark

Submitted 12 May 2003 ; accepted in final form 18 August 2003

Whether the cross-sectional area (CSA) and mechanical properties of the human Achilles tendon change in response to habitual exercise remains largely unexplored. The present study evaluated the CSA and contraction-induced displacement of the aponeurosis-tendon complex of the triceps surae in 11 untrained subjects before (tests 1 and 2) and after (test 3) 9 mo of regular running (78 training sessions). Displacement of the tendon-aponeurosis complex obtained by ultrasonography; electromyography of the gastrocnemius, soleus, and dorsiflexor muscles; and joint angular rotation were recorded during graded isometric plantarflexion ramps. Tendon CSA and moment arm were measured by using MRI, and tendon force was calculated from joint moments and tendon moment arm. A treadmill test was used to determine submaximal oxygen consumption (O₂) at a given speed and maximal O₂. The total running duration was 43 h, distributed over 34 wk. Maximal O₂ increased 8.6% (P < 0.01), and submaximal O₂ decreased 6.2% (P < 0.05). Tendon-aponeurosis displacement during maximal voluntary contraction was unchanged (tests 1–3, 5.2 ± 0.6, 5.2 ± 0.5, and 5.3 ± 0.4 mm, respectively) and yielded a structural stiffness of 365 ± 50, 358 ± 40, and 384 ± 52 N/mm for tests 1–3, respectively (P > 0.05). Tendon CSA also remained unchanged (tests 1–3, 34.2 ± 2.2, 33.9 ± 2.2, and 33.8 ± 2.1 mm², respectively). In conclusion, a total training stimulus of 9 mo of running in previously untrained subjects was adequate to induce significant cardiovascular improvements, although it did not result in any changes in the mechanical properties of the triceps surea tendon-aponeurosis complex or in the dimensions of Achilles tendon.

stiffness; mechanical properties; tendon hypertrophy; collagen

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