Association of previous injury and speed with running style and stride-to-stride fluctuations

Running-related injuries remain problematic among recreational runners. We evaluated the association between having sustained a recent running-related injury and speed, and the strike index (a measure of footstrike pattern, SI) and spatiotemporal parameters of running. Forty-four previously injured and 46 previously uninjured runners underwent treadmill running at 80%, 90%, 100%, 110%, and 120% of their preferred running speed. Participants wore a pressure insole device to measure SI, temporal parameters, and stride length (S_length) and stride frequency (S_frequency) over 2-min intervals. Coefficient of variation and detrended fluctuation analysis provided information on stride-to-stride variability and correlative patterns. Linear mixed models were used to compare differences between groups and changes with speed. Previously injured runners displayed significantly higher stride-to-stride correlations of SI than controls (P=0.046). As speed increased, SI, contact time (T_contact), stride time (T_stride), and duty factor (DF) decreased (P<0.001), whereas flight time (T_flight), S_length, and S_frequency increased (P<0.001). Stride-to-stride variability decreased significantly for SI, T_contact, T_flight, and DF (P≤0.005), as did correlative patterns for T_contact, T_stride, DF, S_length, and S_frequency (P≤0.044). Previous running-related injury was associated with less stride-to-stride randomness of footstrike pattern. Overall, runners became more pronounced rearfoot strikers as running speed increased.