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First published online July 20, 2007
Journal of Experimental Biology 210, 2743-2753 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.003814

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Adaptational responses of the human Achilles tendon by modulation of the applied cyclic strain magnitude

Adamantios Arampatzis^*, Kiros Karamanidis and Kirsten Albracht

German Sport University of Cologne, Institute of Biomechanics and Orthopaedics, Carl-Diem-Weg 6, 50933 Cologne, Germany

View larger version (15K): [in this window] [in a new window]   Fig. 1. Each training day of the intervention protocol consisted of five sets of repetitive (3 s loading, 3 s relaxation) isometric plantar flexion contractions to induce cyclic strain on the triceps surae tendon and aponeurosis. One leg exercised at low-magnitude tendon–aponeurosis strain [55% of the maximum voluntary contraction (MVC)] whereas the other one exercised at high-magnitude tendon–aponeurosis (90% MVC). The total exercise volume (integral of the plantar flexion moment over time) was identical for both legs. Signal: signal displayed on a computer monitor (3 s loading, 3 s relaxation) for controlling the exercise loading. Moment: plantar flexion moment generated during an exercise set.

View larger version (5K): [in this window] [in a new window]   Fig. 2. Plantar flexion moment–time history during a maximum voluntary contraction (MVC) from one participant with superimposed twitches. A superimposed twitch was evoked through a triplet electrostimulation (three 500 µs square-wave pulses separated by 5 ms) at the plateau of the MVC. Three more twitches were evoked after the MVC, when the triceps surae muscles were relaxed. The vertical lines indicate the instant of the electrostimulation.

View larger version (43K): [in this window] [in a new window]   Fig. 3. Ultrasound images of the gastrocnemius medialis (GM) at rest, at 50% of the maximum voluntary contraction (MVC) and at the plateau of the MVC. The elongation of the tendon and aponeurosis was examined at the GM muscle belly at about 50% of its length. The displacement of the analysed cross-point in relation to the skin marker was defined as measured elongation of the tendon and aponeurosis.

View larger version (15K): [in this window] [in a new window]   Fig. 4. Mean curves (N=11) of the ankle angles and tendon–aponeurosis displacement during the maximum voluntary contraction (MVC) at the high-strain-magnitude exercised leg before (pre-exercise) and after (post-exercise) the intervention. The elongation of the tendon and aponeurosis (corrected) was calculated as the difference of measured displacement (measured) and the passive displacement due to ankle joint rotation (passive) of the analysed cross-point at the aponeurosis of the gastrocnemius medialis. tmax: time to achieve maximum tendon force.

View larger version (24K): [in this window] [in a new window]   Fig. 5. Sagittal (A) and transversal (B) magnetic resonance images as well as the digitised Achilles tendon boundaries (C). The sagittal images served to obtain the location of the most proximal aspect of the tuberositas calcanei and the most distal aspect of the soleus muscle. On each transversal image, the boundaries of the Achilles tendon were outlined manually. The length of the Achilles tendon was calculated as the curved path passing through the centroids of the cross sections (C).

View larger version (11K): [in this window] [in a new window]   Fig. 6. Ratio (post- to pre-exercise values) of the maximum plantar flexion moment and strain of the triceps surae tendon and aponeurosis during the maximum voluntary contraction (MVC). *Statistically significant differences to the control group (P<0.05). Statistically significant differences between low- and high-strain-magnitude exercised legs (P<0.05).

View larger version (25K): [in this window] [in a new window]   Fig. 7. Strain values and strain ratio (post- to pre-exercise) at every 100 N calculated tendon force of the triceps surae tendon and aponeurosis during the maximum voluntary contraction (MVC). *Statistically significant differences between pre- and post-exercise values (P<0.05). Statistically significant differences between high-strain-magnitude intervention and the other two groups (P<0.05).

View larger version (13K): [in this window] [in a new window]   Fig. 8. Cross-sectional area (CSA) values of the Achilles tendon before (pre-exercise) and after (post-exercise) the exercise intervention at every 10% of the tendon length. *Statistically significant differences between pre- and post-exercise values (P<0.05).

View larger version (7K): [in this window] [in a new window]   Fig. 9. Ratio (post- to pre-exercise values) of the cross sectional area (CSA) of the Achilles tendon at every 10% of the tendon length. *Statistically significant differences between low- and high-strain-magnitude exercised legs (P<0.05).

View larger version (20K): [in this window] [in a new window]   Fig. 10. Elastic modulus and maximal stress values of the Achilles tendon during the maximum voluntary contraction (MVC) before (pre-exercise) and after (post-exercise) the exercise intervention. *Statistically significant differences between pre- and post-exercise values (P<0.05).