Manipulation of foot strike and footwear increases Achilles tendon loading during running
American Journal of Sports Medicine
SAGE Publications for American Orthopaedic Society for Sports Medicine (AOSSM)
Reason for embargo
This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by SAGE Publications
Background: The Achilles tendon is the most common site of tendon overuse injury in humans. There has been a recent interest in running with a forefoot strike pattern and in minimal shoes, yet evidence is currently limited regarding the combined influence of foot strike and footwear on Achilles tendon loading. Purpose: To investigate the influence of both foot strike and footwear on Achilles tendon loading in habitual rearfoot strike runners. Study Design: Crossover study design Methods: Synchronised kinematic and force data were collected from 22 habitual rearfoot strikers (11 male), who habitually run in non-minimal running shoes, during overground running at 3.6 m.s-1. Participants ran in three different footwear conditions (standard running shoe; minimal running shoe; barefoot) with both a rearfoot strike (RFS) and an imposed forefoot strike (FFS) in each footwear condition. Achilles tendon loading was estimated using inverse dynamics, where the Achilles tendon moment arm was determined using a regression equation. Conditions were compared using a two-way repeated measures ANOVA. Results: Achilles tendon impulse was greater when running with a FFS than a RFS in minimal shoes. Achilles tendon loading rates were higher when running either in minimal shoes or barefoot than in standard shoes, regardless of foot strike. Conclusions: In runners who habitually rearfoot strike in standard running shoes, running in minimal shoes or barefoot increased the rate of tendon loading, and running with a forefoot strike in minimal shoes increased the magnitude of tendon loading. Transitioning to these running conditions may increase the risk of tendinopathy. What is known about this subject? It has been shown that when running with a forefoot strike compared with a rearfoot strike, the internal ankle plantar flexor moment increases, but there are conflicting findings regarding whether this results in an increase in Achilles tendon force. Some of these findings may have been confounded by footwear. What this study adds to existing knowledge This study considered the influence of both foot strike and footwear on Achilles tendon loading during running, as well as their interactive effect. It has added to the knowledge in this area by identifying that foot strike influences the magnitude of loading, whereas footwear influences the rate, amongst habitual rearfoot strikers who are accustomed to running in standard running footwear.