6533b82bfe1ef96bd128e2af

RESEARCH PRODUCT

Mechanical step variability during treadmill running.

subject

description

The present study was designed to study intra-individual step variability measured both on vertical displacement of the body (delta Z) and on step time (delta t) parameters by means of a kinematic arm and during treadmill running. A group of 17 subjects ran successively at 60%, 80%, 100% and 140% of their maximal aerobic velocity (Vamax). The total number of steps analysed was 6116. The absolute delta Z step variability (sigma delta Z) ranged between 5 mm and 21 mm while the absolute delta t variability (sigma delta t) ranged between 6 ms and 40 ms. Step variabilities were due to step asymmetry (from 38.5% to 48.5% of the step variability) and to stride variability. For submaximal velocities (60%, 80%, and 100% Vamax) both sigma delta t and sigma delta Z were independent of velocity or body dimensions whereas differences between subjects were significant (P0.01) for sigma delta Z. On the other hand, variabilities were significantly increased when velocity was changed from submaximal to the 140% Vamax level. Furthermore, at submaximal levels sigma delta Z was linked to the subject's energy cost of running (P0.05). Therefore, the intra-individual step variability should not be neglected in future studies on mechanical efficiency of running and it is suggested that, to obtain a good accuracy (better than 1%, P0.05) on mean value and variability of the mechanical parameters, measurements should be performed on at least 32-64 consecutive steps, which corresponds to about 15 to 20s of running.