Agreement between an inertial measurement unit (IMU) algorithm and a photoelectric system for analysing spatiotemporal variables during overground and treadmill running.

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.