Validity and Reliability of a Commercial Fitness Watch for Measuring Running Dynamics

STUDY DESIGN: Validity and reliability study. BACKGROUND: Providing feedback on running mechanics is a common intervention to decrease the risk of 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 the validity and reliability of these measures. OBJECTIVE: To determine the validity and reliability of measures of cadence, GCT, and VO with a fitness watch compared to a motion-analysis system. METHODS: Twenty runners ran in 3 conditions: (1) baseline (self-selected speed and cadence), (2) higher cadence, and (3) decreased vertical motion (minimal oscillation). Ten runners also performed an additional baseline running session to measure intrasession reliability. For each condition, the average cadence, GCT, and VO were collected from a watch and from a motion-capture system. Intraclass correlation coefficients (ICCs) were used to assess validity between devices. An analysis of variance with 2 repeated measures was used to determine the ability of the watch and motion analysis to detect change in running dynamics. RESULTS: The ICCs between the 2 measuring systems were 0.931, 0.963, and 0.749 for cadence, VO, and GCT, respectively (P<.01). The minimal detectable changes at the 95% confidence interval for cadence, VO, and GCT were 2.53 steps per minute, 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.