Whipping or tearing? The biomechanics of Achilles tendinopathy in rearfoot strike runners

Background

Two biomechanical mechanisms for the development of Achilles tendinopathy in runners have been proposed: A whipping mechanism characterized by prolonged and excessive rearfoot eversion, and a tearing mechanism characterized by high eccentric plantar flexor forces. The purpose of this pilot study was to determine if runners with and without a history of Achilles tendinopathy exhibited gait biomechanics consistent with either of these mechanisms.

Methods

Seven male runners with previous or current Achilles tendinopathy and seven healthy male control runners were evaluated by three-dimensional gait analysis. Peak rearfoot eversion angle, rearfoot eversion excursion, duration of rearfoot eversion, and peak rearfoot inversion angle were compared between groups to evaluate the whipping mechanism of injury. Peak dorsiflexion angle, peak dorsiflexion velocity, and peak ankle power absorption were compared between groups to evaluate the tearing mechanism. Additionally, rearfoot eversion angle and sagittal plane ankle power waveforms were compared between groups using statistical parametric mapping.

Findings

There were no differences in any rearfoot eversion, inversion, or dorsiflexion variables or waveforms during running in the Achilles tendinopathy group compared to controls.

Interpretation

Rearfoot strike runners with Achilles tendinopathy do not exhibit running biomechanics consistent with either the whipping or tearing mechanisms of injury.