Reliability of Inertial Measurement Unit-Based Spatiotemporal and Kinetic Variables in Endurance Runners during Treadmill Running.

Wearable technology for running analysis is growing in both sports science research and applied fields. This study examined the reliability of some spatiotemporal and kinetic variables estimated from an inertial measurement unit (IMU) fastened over the lumbar spine. Eighteen recreational endurance runners performed two maximal incremental treadmill running tests during a 7-10 day period under standard conditions. Contact time (CT), stride time (ST), stride length (SL), stride frequency (SF), as well as anteroposterior (AP) impulses and vertical (VT) peak brake data were analysed at 9, 15 and 21 km•h^-1. Test-retest reliability was measured as the intraclass correlation coefficient (ICC), the coefficient of variation (CV) and minimal detectable change (MDC). No significant differences between tests were observed (p > 0.05; effect size (ES) < 0.28; trivial to small). Reliability increased from 9 to 21 km•h^-1 (ICC from 0.88 to 0.93; ES = 1.0; moderate) and was higher in spatiotemporal (CV < 2.3%) than kinetic variables (CV < 6.8%). This study adds novel data regarding the reliability of the MTw IMU. The results reported in this study enable researchers to determine whether the changes in IMU-derived data are outside of the measurement error following training and rehabilitation settings.