Effect of 5% body weight forward pulling on dynamics of treadmill running

Abstract

Forward pulled running on a treadmill is known to increase mechanical and decrease metabolic constrains relative to normal running. This experimental situation was used to investigate the variations of the mechanical parameters induced by the pulling. Ten subjects ran during 3 min at individually predetermined constant speeds of 16.4 ± 1.4 km • h -1 on a treadmill while being forward pulled by a load equal to 5% of their body weight. Ground reaction forces were recorded during the last 30 s of the run. Kinematic parameters of the stride as well as impulses and mechanical work were then calculated. Stride frequency did not change, while horizontal impulses were highly modified (+38% and -28%, respectively, for the braking and pushing impulses). Simultaneously, external work produced during the braking and pushing phases was modified by +6.5% and -4.7%, respectively. Therefore, the horizontal impulses were far more modified than the mechanical work. As a consequence, the estimation of the relative influence of negative (braking) and positive (push-off) phases on metabolic cost of running could be quite different when forces, impulses, or work are considered.