Minimum time required for assessing step variability during running at submaximal velocities.

This study aimed to determine the minimum time required for assessing spatiotemporal variability during continuous running at different submaximal velocities and, thereby, the number of steps required. Nineteen trained endurance runners performed an incremental running protocol, with a 3-min recording period at 10, 12, 14 and 16 km/h. Spatiotemporal parameters (contact and flight times, step length and step frequency) were measured using the OptoGait system and step variability was considered for each parameter, in terms of within-participants standard deviation (SD) and coefficient of variation (CV%). Step variability was considered over six different durations at every velocity tested: 0-10 s, 0-20 s, 0-30 s, 0-60 s, 0-120 s and 0-180 s. The repeated measures ANOVA revealed no significant differences in the magnitude of the four spatiotemporal parameters between the recording intervals at each running velocity tested (p ≥ 0.05, ICC > 0.90). The post-hoc analysis confirmed no significant differences in step variability (SD and CV% of each spatiotemporal parameter at any velocity tested) between measurements. The Bland-Altman limits of agreement method showed that longer recording intervals yield smaller systematic bias, random errors, and narrower limits of agreement, regardless of running velocity. The results suggest that the duration of the recording period required to estimate spatiotemporal variability plays an important role in the accuracy of the measurement, regardless of running velocity (10-16 km/h).