A comparison of negative joint work and vertical ground reaction force loading rates in Chi runners and rearfoot-striking runners.

STUDY DESIGN Observational. OBJECTIVES To compare lower extremity negative joint work and vertical ground reaction force loading rates in rearfoot-striking (RS) and Chi runners. BACKGROUND Alternative running styles such as Chi running have become a popular alternative to RS running. Proponents assert that this running style reduces knee joint loading and ground reaction force loading rates. METHODS Twenty-two RS and 12 Chi runners ran for 5 minutes at a self-selected speed on an instrumented treadmill. A 3-D motion analysis system was used to obtain kinematic data. Average vertical ground reaction force loading rate and negative work of the ankle dorsiflexors, ankle plantar flexors, and knee extensors were computed during the stance phase. Groups were compared using a 1-way analysis of covariance for each variable, with running speed and age as covariates. RESULTS On average, RS runners demonstrated greater knee extensor negative work (RS, -0.332 J/body height × body weight [BH·BW]; Chi, -0.144 J/BH·BW; P<.001), whereas Chi runners demonstrated more ankle plantar flexor negative work (Chi, -0.467 J/BH·BW; RS, -0.315 J/BH·BW; P<.001). RS runners demonstrated greater average vertical ground reaction force loading rates than Chi runners (RS, 68.6 BW/s; Chi, 43.1 BW/s; P<.001). CONCLUSION Chi running may reduce vertical loading rates and knee extensor work, but may increase work of the ankle plantar flexors.