An evaluation of different protocols for measuring the force-velocity relationship of the human quadriceps muscles

Abstract

A modified Cybex II isokinetic dynamometer was used to evaluate the problems associated with measuring the concentric force-velocity characteristics of human knee extensor muscles. Three contraction protocols were investigated, simple voluntary contractions (VC); releases from maximal voluntary isometric contractions (VR) and releases from isometric femoral nerve stimulated contractions (FNR). Percutaneous stimulation of the quadriceps was unsuitable for dynamic contractions as the proportion of the muscle activated varied with the angle of knee flexion. Isometric length-tension relationships and isokinetic contractions at seven angular velocities between 0.5 and 5.2 rad.s-1 were recorded in five subjects. During isometric and slow dynamic contractions the voluntary forces were often greater than those obtained by femoral nerve stimulation, probably due to subjects stretching the rectus femoris during voluntary manoeuvres. It was found that the VC protocol produced acceptable isokinetic force recordings only at velocities below 3.1 rad.s-1 in most subjects whilst VR contractions resulted in unexpectedly low forces at velocities below 1.57 rad.s-1. Of the three techniques employed, FNR, although uncomfortable for subjects, provided the most accurate and reliable method of measuring force-velocity characteristics of knee extensor muscles. FNR contractions produced a force-velocity curve which showed a smooth decline in force with increasing velocity up to 5.2 rad.s-1. VC contractions appear to be an acceptable alternative for testing the muscles provided the angular velocity is less than 3.1 rad.s-1 and the subjects can be prevented from stretching the rectus femoris during the movement.

Determining Subject-Specific Torque Parameters for Use in a Torque-Driven Simulation Model of Dynamic Jumping

“…The torque / angular velocity data collected exhibited a plateau at low concentric angular velocities similar to the data collected in previous studies (e.g. James et al, 1994). The reason for the plateau could be due to a number of factors including propagation of the double plateau result of Edman for single fibres to joint torques, differential activation, changing moment arms and the effect of muscles acting in concert around the joint.…”

“…However, more complex double hyperbolic force-velocity relationships have been reported for single muscle fibres (Edman, 1988). Furthermore similar double hyperbolic relationships have been obtained for the net torque about a joint as a function of angular velocity using an isovelocity dynamometer (James et al, 1994). In addition a quadratic convex relationship has been reported for the force-length relationship of 'in vitro muscle preparations' (Gordon et al, 1966) although the relationship around a joint appears more complex with the interaction of different muscles.…”

“…Since isovelocity torque / angular velocity data often has a double hyperbolic shape (James et al, 1994) rather than a single hyperbolic shape a function was chosen to fit the isovelocity data which could represent either form and also include eccentric movement. The torque / angular velocity relationship of the contractile component was modelled using a six parameter exponential function (equation (4)).…”

Modelling the maximum voluntary joint torque/angular velocity relationship in human movement

“…As a consequence the seven parameter function of Subject 1 shows a pronounced plateau for low concentric velocities whereas that of Subject 2 is closer to a hyperbola with concave curvature for all concentric velocities (Figures 3a, 4a). This plateau in the torque data of Subject 1 at low concentric velocities is evident in previous studies (Dudley et al, 1990;James et al, 1994;King and Yeadon, 2002) and a seven parameter function is required in order to fit such data reasonably. On the other hand the data of Subject 2 shows no such plateau and in such a case a reasonable fit should be possible using a five parameter function in which the maximum eccentric to isometric torque ratio is a free parameter.…”

Assessing Voluntary Muscle Activation with the Twitch Interpolation Technique

“…because the often studied biceps brachii can be almost fully activated while the brachioradialis exhibits a significant activation deficit [15] . Furthermore, small increases in muscle length that occur during supposedly isometric contractions of near-maximal and maximal intensity [15,36] become asymptotic at considerably submaximal forces [37] . Consequently, care must be taken to prevent muscles from shortening during superimposed responses and failure to do so will impact upon estimates of voluntary activation regardless of how it is quantified.…”