Algorithm for extracting initial and terminal contact timings during treadmill running using inertial sensors

Inertial measurement units (IMUs) are now considered as an economical solution for long term assessment in real conditions. However, their use in running gait analysis is relatively new and limited. Detecting the timing at which the foot strikes the ground (initial contact, IC) and the timing at which the foot leaves the ground (terminal contact, TC) gives access to many relevant temporal parameters such as stance, swing or stride durations. In this paper, we present an original algorithm to extract IC and TC timings and associated parameters from running data. These data have been measured using a newly developed IMU-based hardware system in ten asymptotic participants who ran at three speeds (slow, normal, and fast) with different running patterns (natural, rearfoot strike, mid-foot strike, and forefoot strike). This algorithm has been validated against a 200 Hz video camera based on 7056 IC and TC timings and 6861 temporal parameters. This algorithm extracted ICs and TCs with an accuracy and precision of (median [1st quartile; 3rd quartile]) 5 ms [-5 ms, 15 ms] and 0 ms [-5 ms, 5 ms], respectively. The relative errors in the extraction of stride and stance durations are -1.56 ± 3.00% and 0.00 ± 1.32%, respectively.