An exploration of the acute response of the asymptomatic Achilles tendon to exercise using diagnostic ultrasound. A systematic review of cohort studies

Objectives: To describe the acute effects of exercise on the morphology, mechanical properties and blood flow of the Achilles tendon, as measured with ultrasound.

Design: Systematic review of cohort studies.

Methods: Seven electronic research databases were systematically searched for exercise intervention-based studies reporting morphology, mechanical properties and blood flow of the Achilles tendon, as measured with ultrasound.

Results: Searches revealed 2460 possible articles and 35 satisfied the inclusion criteria. There is evidence that eccentric heel drops resulted in a reduction in the diameter and cross-sectional area of the tendon whilst running/stretch-shortening cycle activities did not result in a change. The latter did not affect tendon mechanical properties. Tendon blood flow was consistently increased in response to exercise.

Conclusions: The acute response of the Achilles tendon to exercise showed an increase in blood flow and a reduction in diameter following heel drop exercises. Exercise modes were relevant since eccentric and isometric loading resulted in a greater response in the tendon. Activities like running and hopping placing specific demands on the tendon's spring function resulted in a minimal change in tendon morphology and no change in mechanical properties.