Effects of passive ankle dorsiflexion stiffness on ankle mechanics during drop landings

Objectives: Vertical landing tasks strain the Achilles tendon and plantar-flexors, increasing acute and overuse strain injury risk. This study aimed to determine how passive ankle dorsiflexion stiffness affected ankle mechanics during single limb drop landings at different vertical descent velocities. Design: Cross-sectional study. Methods: Passive ankle dorsiflexion stiffness and passive weight-bearing dorsiflexion range of motion (DROM) were quantified for 42 men. Participants were then grouped as having low (LPS: 0.94 +/- 0.15 Nm(o-1); n = 16) or high (HPS: 2.05 +/- 0.36 Nm(o-1); n = 16; p < 0.001) passive ankle dorsiflexion stiffness. Three-dimensional ankle joint kinematics was quantified while participants performed drop landings onto a force platform at two vertical descent velocities (slow: 2.25 +/- 0.16 m s(-1); fast: 3.21 +/- 0.17 m s(-1)). Results: Although affected by landing velocity, there were no significant effects of passive ankle dorsiflexion stiffness, nor any significant ankle dorsiflexion stiffness x vertical descent velocity interactions on any outcome variables characterising ankle mechanics during drop landings. Furthermore, there was no significant difference between the groups for passive weight-bearing DROM (LPS: 43.9 +/- 4.1(o); HPS: 42.5 +/- 5.7(o)), indicating that the results were not confounded by between-group differences in ankle range of motion. Conclusions: Neither high nor low passive ankle dorsiflexion stiffness was found to influence ankle biomechanics during drop landings at different descent velocities. Landing strategies were moderated more by the demands of the task than by passive ankle dorsiflexion stiffness, indicating that passive ankle dorsiflexion stiffness may not affect plantar-flexor strain during a drop landing. (c) 2012 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.