Eccentric calf muscle exercise produces a greater acute reduction in Achilles tendon thickness than concentric exercise.

OBJECTIVE To investigate the acute effects of isolated eccentric and concentric calf muscle exercise on Achilles tendon sagittal thickness. DESIGN Within-subject, counterbalanced, mixed design. SETTING Institutional. PARTICIPANTS 11 healthy, recreationally active male adults. INTERVENTIONS Participants performed an exercise protocol, which involved isolated eccentric loading of the Achilles tendon of a single limb and isolated concentric loading of the contralateral, both with the addition of 20% bodyweight. MAIN OUTCOME MEASUREMENTS Sagittal sonograms were acquired prior to, immediately following and 3, 6, 12 and 24 h after exercise. Tendon thickness was measured 2 cm proximal to the superior aspect of the calcaneus. RESULTS Both loading conditions resulted in an immediate decrease in normalised Achilles tendon thickness. Eccentric loading induced a significantly greater decrease than concentric loading despite a similar impulse (-0.21 vs -0.05, p<0.05). Post-exercise, eccentrically loaded tendons recovered exponentially, with a recovery time constant of 2.5 h. The same exponential function did not adequately model changes in tendon thickness resulting from concentric loading. Even so, recovery pathways subsequent to the 3 h time point were comparable. Regardless of the exercise protocol, full tendon thickness recovery was not observed until 24 h. CONCLUSIONS Eccentric loading invokes a greater reduction in Achilles tendon thickness immediately after exercise but appears to recover fully in a similar time frame to concentric loading.