Development and validation of a new simulator of running impacts

Understanding the mechanics of impacts during human locomotion is a current challenge for injury prevention, quantification of training loads and equipment design. The present study aimed to validate a new ergometer able to reproduce and measure impacts experienced during human locomotion, after a frequency-domain decomposition. An ergometer was designed as a physical pendulum equipped with a weighted force plate released from a given angle and subjected to gravitational acceleration until it contacts, at its lowest point, the foot of the participant lying supine. The reliability of the generated impact properties was assessed on twenty participants using a test-retest procedure. The validity was evaluated on ten participants, by comparing ten individualized impacts produced by the ergometer to ten foot-ground impacts experienced while running at 10 km/h. A Discrete Fourier Transform was used to decompose the raw force signal into high-frequency (impact force) and low-frequency (active force) components. The signal was then recomposed into the time domain with inverse Fourier transform. Key variables (impact peak force and loading rate) were subsequently calculated. Consistent intra- and inter-session reliability of these variables were obtained with acceptable coefficients of variation (from 15 % to 22 %). Bland-Altman analysis showed slight but significant higher impact peak forces during the retest, suggesting the need for a familiarization session. The impacts from the ergometer correlated at 0.98 with those measured during running, associated with low variation between them (<10 %). This ergometer provides a valid tool for reproducing locomotion-related impacts and studying their beneficial or deleterious effects on the human body.