Challis, JH

Winter, SL

English

Kent Academic Repository

The force-length relationship in vivo: a simulation study   S.L.Winter1, & J.H.Challis2   1Aberystwyth University and 2The Pennsylvania State University  The force-length relationship of muscle is a fundamental mechanical property of muscle and an important determinant of resultant joint moments.  In vivo a muscle may operate over all or only part (ascending limb, descending limb or plateau region) of the force-length curve for physiologically realistic ranges of motion.  There are several possible sources of this variability, for example anatomical and architectural differences and differences in muscle-tendon mechanical properties.  Such features are reflected in the parameters usually included in muscle models.  Reported values for these parameters typically vary between different muscles and vary between subjects for a given muscle.  The purpose of this study was to determine the effect of these parameters on the section of the force-length relationship that a muscle operates over.  A generalised model of a mono-articular muscle-tendon complex operating over a 90 degree joint range of motion was formulated and variables were systematically varied.  The parameters investigated were: ratio of tendon resting length to muscle fibre optimum length ( OPTTR Lf/L ) (varied from 0.5 to 11.5), ratio of muscle fibre optimum length to average moment arm ( r/LfOPT ) (0.5 to 5), normalised tendon strain at maximum isometric force (c) (0 to 8%), muscle fibre pennation angle ( PENN ) (0 to 45 degrees).  The joint angle at which the optimum muscle fibre length occurred ( REF ) was varied throughout the 90 degree range of motion.  The values for each parameter were based on reported ranges for five mono-articular muscles with different functional roles.  It was shown that OPTTR Lf/L  was important in determining the section of the force-length relationship that a muscle operated over.  The effect of this ratio was modulated by r/LfOPT .  The muscle operated over only one limb at intermediate values of these two ratios (OPTTR Lf/L =5; r/LfOPT =3), whether this was the ascending or descending limb was determined by the precise relative values of c, PENN , REF , and OPTTR Lf/L .  At higher values of the two ratios the whole force-length relationship was used, at lower values only a small section of one limb was used.  It was concluded that that inter-individual variability in the expressed section of the force-length relationship is possible, particularly for muscles with intermediate values of r/LfOPT  and OPTTR Lf/L  such as the brachialis and vastus lateralis.  These results have implications for understanding the training adaptations of muscles for sport. 

The force-length relationship in vivo: a simulation study

http://kar.kent.ac.uk/53277/1/BASES_Abstract_2008.pdf

The force-length relationship in vivo: a simulation study

Abstract

Similar works

Full text

Available Versions

Kent Academic Repository