The JUMPING project (2002 - 2006)

Acronym: JUMPING
Name: Expertise signatures in jumping behaviour
Type: Collaborative project
Funding: French Institut Universitaire de France, Univ. Paris Sud 11
UM1 key researcher: Benoît Bardy
Collaborator: Guillaume Laffaye (Univ. Paris Sud 11)

JUMPING is a theoretical and experimental project aiming at identifying the movement signatures of expert jumpers

Theory:

During running or bouncing, bipedal animals use musculoskeletal springs to alternately store and restitute elastic energy (Cavagna et al., 1977). In the run and jump transition, muscles, tendons and ligaments collectively behave like a linear spring, store kinetic energy during the run-up and restitute it during the jump in the form of potential gravitational energy.

Simple mass-spring systems consisting of a single linear spring representing the leg, attached to a point summarizing body mass, have been shown to capture efficiently the mechanics of running or jumping (Blickhan, 1989; Mac Mahon and Cheng, 1990; Seyfarth et al., 1999).

The stiffness of the spring (i.e., leg stiffness or kleg) can be defined in different ways and at different levels of analysis, but its accurate contribution to jumping performance is still matter of debate.

In particular, the dynamics of kleg in one-leg vertical jumps (such a in high jumping) is still unknown. The goal of this project is to investigate: a) the leg spring behavior in the one leg vertical jump, b) the contribution of impulse parameters to this behavior, c) the effect of jumping expertise on kleg.

Experiments:

The experiments conducted so far involved different categories of experts (hand-ball, basket-ball, volley-ball players and Fosbury athletes), as well as novice subjects. Their task was to perform a run-and-jump test in order to touch a ball with the head.

Several experimental conditions were tested from 55% to 95% of the maximum jump height. Kinematic and kinetic data were collected using 6 cameras and a force plate. The mechanical behavior of the musculo-skeleton component of the human body was modelled as a simple mass-spring system, from which leg stiffness values could be extracted in order to better understand energy transfer during running or jumping. Leg stiffness was determined as the ratio between maximal ground reaction force and leg shortening.

The main results indicate that leg stiffness (mean value of 11.5 kN/m) decreased with jumping height. Leg shortening at take-off also increased with jumping height, while 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. Different PCA profiles were found for the four jumping expertise, revealing subtle but specific strategies in the run-and-jump task.

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.

Main result: Factor scores for each participant (mean value by subject) on the two rotated principal components. The x-axis represents the first principal component (bringing together contact time CT, leg stiffness Kleg and vertical maximum force scaled to body mass Frel) and the y-axis represents the second principal component (linking leg compression Δr and jumping height Dmax ). Left and bottom parts: numbers represent individual scores; right and upper parts: numbers represent the factor scores.

The analysis performed on the sport categories indeed revealed different jumping profiles, characterized by specific, sport-related, impulse parameters. Volley-ball and basket-ball jumpers were characterized by the first PCA component, revealing long contact time, low vertical force and reduced leg stiffness.

In contrast, Fosbury athletes exhibited an important leg shortening, according to the second PCA component.

Key references (downloadable version in page Vitae):

1. Laffaye, G., Bardy, B. G., & Durey, A. (2005). Leg stiffness and expertise during jumping. Medecine & Science in Sports & Exercise, 37, 536-543.
2. Laffaye, G., Taiar, R., & Bardy, B. G. (2005). Effet de l’instruction sur la régulation de la raideur de la jambe lors de sauts de contre-haut. Science & Sports, 20, 136-143.
   
3. Laffaye, G., Bardy, B. G, & Taiar, R. (2006). Upper-limb motion and drop jump: effect of expertise. Journal of Sports Medicine and Physical Fitness, 46, 238-247.
4. Laffaye, G., Bardy, B. G., & Durey, A. (2007). Principal component structure and sport-specific difference in the running one-leg vertical jump. International Journal of Sport Medecine, 28, 420-425.