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Biomechanical Analysis of Injured Minimalist Runners

Matthew Salzler, M.D.

Minimalist runners have been shown to have different biomechanics with lower impact forces than habitually shod runners. Running in minimalist footwear has been promoted as a means of reducing or eliminating running injuries by returning to a more natural running pattern with a forefoot strike. We recently reported a case series of injuries observed in minimalist runners. The biomechanics of injured minimalist runners may deviate from the previously described barefoot running pattern. The purpose of this study was to identify biomechanical risk factors that may predispose minimalist runners to injury.

Seven minimalist runners (average weekly mileage > 20 km/week) status post recovery from injuries sustained in minimalist footwear underwent 3 dimensional biomechanical running analysis at the Sports Performance Center. Each subject was asked to run continuously at their natural pace in our motion capture area. Primary variables measured included vertical ground reaction force, impact transient force, vertical compliance, and center of mass. Ankle, knee and hip kinematics were analyzed throughout the run cycle.

Four of the seven previously injured minimalist runners demonstrated a rearfoot strike and three utilized a forefoot strike. Five of the seven had impact transient peaks with an average impact transient force of 1.12 +/- 0.59 (bodyweights per second); the average impact transient for the rearfoot runners was 1.56 +/- 0.29 as compared to 0.54 +/- 0.13 for the forefoot runners (p<0.001). The mean loading rate was 115 +/- 47 (bodyweights per second) with a mean of 170 +/- 22 in the rearfoot runners and 42 +/- 5 in the forefoot runners (p< 0.001). The mean vertical compliance was 0.0109 +/- 0.0075 (dimensionless) with a mean of 0.0050 +/- 0.0008 in the rearfoot runners and 0.0187 +/- 0.0024 in the forefoot runners (p<0.001). The mean overstride distance was 10.42 +/- 1.36 cm with a mean of 10.42 +/- 1.36 in the rearfoot runners and 7.18 +/- 1.06 in the forefoot runners (p < 0.001).

Injured minimalist runners utilize both forefoot and rearfoot strikes resulting in subsequent differences across impact transient forces, loading rates, vertical compliance, and kinematics. The biomechanics of the majority of injured minimalist runners more closely resemble that of habitually shod runners than of habitually barefoot runners.