The aim of this study was to assess the agreement between running stride variables measured simultaneously with an inertial sensor (MTw IMU) using a specific algorithm, and a floor-based photoelectric (Optojump; OJ) system among well-trained endurance runners, during overground and treadmill runs at speeds ranging from 9 to 21 km·h-1. Five different filter settings (from 0_0 to 4_4) were used with the OJ to detect the contact event, based on the number of LEDs (from 1 to 5). No significant differences (p > 0.05) were found between the two devices in any of the stride variables when the 4_4 filter was implemented using the OJ. The agreement was good for contact time (CT) and flight time (FT) [r = 0.81-0.93; Typical error of the estimate (TEE%) = 3.2-7.5%], whereas for stride frequency (SF), stride length (SL) and stride time (ST) the agreement was almost perfect (r = 0.91-0.99; TEE% = 0.2-1.7%). The agreement worsened as the number of activated LEDs used to detect the contact event decreased. This suggests that the tested inertial sensor using a specific algorithm can achieve highly precise measurement of spatiotemporal parameters during both overground and treadmill running, compared to the OJ (4_4) system.
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