Article

The muscle force-stiffness relationship has often been modeled as linear, while in situ muscle research has clearly demonstrated non-linearity. Estimation of rotational joint stability relies on both a muscle's instantaneous pre-perturbation force and stiffness. Under conditions of static equilibrium, a muscle's stiffness will function in a stabilizing manner, while its force can function in either a stabilizing or destabilizing manner depending on the muscle's orientation about the joint. Methods. A single muscle (rectus abdominis) was modeled and its individual direct stabilizing potential about the L4-L5 spine joint was analyzed. Three force-stiffness relationships were examined: (1) linear; (2) non-linear with moderate stiffness magnitudes; (3) non-linear with higher stiffness magnitudes. Findings. With a linear force-stiffness relationship, stability increased proportional to muscle force; with a non-linear relationship, stability peaked and subsequently decreased at submaximal muscle forces. When considering the lower, as opposed to the higher non-linear stiffness magnitudes, the stabilizing potential of the muscle peaked at a lower muscle force level and actually became negative (destabilizing) at a critical stiffness magnitude. Interpretation. It was concluded that a non-linear muscle force-stiffness relationship greatly alters the individual stabilizing potential of the muscle throughout its progression of force development. A muscle's stabilizing contribution may actually peak at and subsequently decrease above a critical submaximal force level. Incorporating this knowledge into stability models may assist in recognizing unstable events that lead to injury at higher levels of muscle activation. (c) 2005 Elsevier Ltd. All rights reserved.

Langue : ANGLAIS