Leg stiffness and expertise in men jumping.
OBJECTIVE
The aim of the present study is to investigate: a) the leg spring behavior in the one-leg vertical jump, b) the contribution of impulse parameters to this behavior, and c) the effect of jumping expertise on leg stiffness.


METHODS
Four categories of experts (handball, basketball, volleyball players, and Fosbury athletes), as well as novice subjects performed a run-and-jump test to touch a ball with the head. Five experimental conditions were tested from 55 to 95% of the maximum jump height. Kinematic and kinetic data were collected using six cameras and a force plate.


RESULTS
The mechanical behavior of the musculoskeleton component of the human body can be modeled as a simple mass-spring system, from which leg stiffness values can be extracted to better understand energy transfer during running or jumping. The results indicate that leg stiffness (mean value of 11.5 kN.m) decreased with jumping height. Leg shortening at takeoff also increased with jumping height, whereas contact time decreased (-18%). No difference was found between experts and novices for leg stiffness. However, a principal components analysis (PCA) indicated the contribution of two main factors to the performance. The first factor emerged out of vertical force, stiffness, and duration of impulse. The second factor included leg shortening and jumping height.


CONCLUSIONS
Differences between experts and novices were observed in terms of the contribution of leg stiffness to jump height, and more importantly, clear differences existed between experts in jumping parameters. The analysis performed on the sport categories indeed revealed different jumping profiles, characterized by specific, sport-related impulse parameters.
Laffaye
Guillaume
G
Center for Research in Sport Sciences, University Paris XI, Paris, FRANCE. eglaffaye@aol.com
Bardy
Benoît G
BG
Durey
Alain
A
D000328:Adult; D001696:Biomechanical Phenomena; D003625:Data Collection / Q000379:methods; D006801:Humans; D007700:Kinetics; D007866:Leg / Q000502:physiology*; D008124:Locomotion / Q000502:physiology; D008297:Male; D008954:Models, Biological; D025341:Principal Component Analysis / Q000379:methods; D013177:Sports / Q000502:physiology*