Faster top running speeds are achieved with greater ground forces not more rapid leg movements

Abstract

We twice tested the hypothesis that top running speeds are determined by the amount of force applied to the ground rather than how rapidly limbs are repositioned in the air. First, we compared the mechanics of 33 subjects of different sprinting abilities running at their top speeds on a level treadmill. Second, we compared the mechanics of declined (-6 degrees ) and inclined (+9 degrees ) top-speed treadmill running in five subjects. For both tests, we used a treadmill-mounted force plate to measure the time between stance periods of the same foot (swing time, t(sw)) and the force applied to the running surface at top speed. To obtain the force relevant for speed, the force applied normal to the ground was divided by the weight of the body (W(b)) and averaged over the period of foot-ground contact (F(avge)/W(b)). The top speeds of the 33 subjects who completed the level treadmill protocol spanned a 1.8-fold range from 6.2 to 11.1 m/s. Among these subjects, the regression of F(avge)/W(b) on top speed indicated that this force was 1.26 times greater for a runner with a top speed of 11.1 vs. 6.2 m/s. In contrast, the time taken to swing the limb into position for the next step (t(sw)) did not vary (P = 0.18). Declined and inclined top speeds differed by 1.4-fold (9.96+/-0.3 vs. 7.10+/-0.3 m/s, respectively), with the faster declined top speeds being achieved with mass-specific support forces that were 1.3 times greater (2.30+/- 0.06 vs. 1.76+/-0.04 F(avge)/ W(b)) and minimum t(sw) that were similar (+8%). We conclude that human runners reach faster top speeds not by repositioning their limbs more rapidly in the air, but by applying greater support forces to the ground.

Accounting for elite indoor 200 m sprint results

“…The constant L stance assumption is broadly supported by a range of empirical data (Cavagna et al 1976;Greene & McMahon 1979;Greene 1985;Weyand et al 2000). Our model deviates subtly from that of Greene (1985) in that we assume protraction time-the time taken to swing the leg forwards (t swing ) between each stance period for that leg-to be constant, rather than assuming a constant stride frequency.…”

“…The kinematic parameters are derived from observations reported by Weyand et al (2000), in which the relevant values are shown to be remarkably consistent and independent of sprint performance, at least within each gender. We, therefore, use t swing Z 0.315 s for male and female, and L stance Z0.99 m (male) or 0.90 m (female).…”

“…Instead, we assume that the leg is protracted at maximum velocity under all conditions, keeping t swing constant and allowing stride frequency to vary slightly. While this development does add a further empirical term to the model, we feel the assumption to be more justifiable, and maximally performing sprinters of a range of standards achieve very similar values for t swing (Weyand et al 2000), so there is little added complexity.…”

Does maximising ball speed in cricket fast bowling necessitate higher ground reaction forces?

“…Within many sporting activities, techniques that maximise performance cause larger forces and loading rates (Weyand et al, 2000) to be exerted on the body, potentially increasing the likelihood of injury (in the context of fast bowling, maximising performance can be considered as delivering the ball as fast as possible in the desired direction). In cricket fast bowling it has been suggested that bowlers who release the ball at faster speeds experience higher peak ground reaction forces and loading rates (Portus et al, 2004).…”

Return to sport following hip injury

“…It has also been suggested that "over speed" training or fast velocity running is beneficial for improving cardiovascular and neuromuscular function [21]. It has been demonstrated that this type of training is effective at producing greater rates of muscular force generation [22,23]. Traditional "over speed" training must be approached cautiously because of increased peak ground reaction forces that accompany running at fast velocity.…”