Study Design: Validity and reliability study. Bckground: Providing feedback on running mechanics is a common intervention to decrease the risk for injury or to restore running after an injury. Commercially available devices are able to measure running dynamics, such as cadence, ground contact time (GCT), and vertical oscillation (VO), but there is limited evidence on their validity and reliability. Objective: To determine the validity and reliability of measuring cadence, GCT, and VO with a fitness watch compared to a motion analysis system. Methods: Twenty runners ran in three conditions: 1) baseline (self-selected speed and cadence), 2) higher cadence run, and 3) decreased vertical motion run (minimal oscillation). Ten runners also performed an additional baseline running session to measure intrasession reliability. For each condition the average cadence, GCT, and VO was collected from a watch and a motion capture system. Intraclass correlation coefficients (ICC) were used to assess validity between devices. ANOVAs with two repeated measures were used to determine the ability of the watch and motion analysis to detect change in running dynamics. Results: The ICCs between the two measuring systems were 0.931, 0.963, 0.749 for cadence, VO, and GCT, respectively (p < 0.01). The MDC95 for cadence, VO and contact time were 2.53 steps/min, 0.45 cm, and 0.01 seconds, respectively, for the watch. There were no interaction effects, but there was a main effect for condition; both devices detected changes in running dynamics. Conclusion: The watch is a valid and reliable tool for detecting changes in cadence, VO, and GCT.
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