Observations on force enhancement in submaximal voluntary contractions of human adductor pollicis muscle

Abstract

It has been observed consistently and is well accepted that the steady-state isometric force after active muscle stretch is greater than the corresponding isometric force for electrically stimulated muscles and maximal voluntary contractions. However, this so-called force enhancement has not been studied for submaximal voluntary efforts; therefore, it is not known whether this property affects everyday movements. The purpose of this study was to determine whether there was force enhancement during submaximal voluntary contractions. Human adductor pollicis muscles (n = 17) were studied using a custom-built dynamometer, and both force and activation were measured while muscle activation and force were controlled at a level of 30% of maximal voluntary contraction. The steady-state isometric force and activation after active stretch were compared with the corresponding values obtained during isometric reference contractions. There was consistent and reliable force enhancement in 8 of the 17 subjects, whereas there was no force enhancement in the remaining subjects. Subjects with force enhancement had greater postactivation potentiation and a smaller resistance to fatigue in the adductor pollicis. We conclude from these results that force enhancement exists during submaximal voluntary contractions in a subset of the populations and suggest that it may affect everyday voluntary movements in this subset. On the basis of follow-up testing, it appears that force enhancement during voluntary contractions is linked to potentiation and fatigue resistance and therefore possibly to the fiber-type distribution in the adductor pollicis muscle.

Force–time history effects in voluntary contractions of human tibialis anterior

“…For contractions performed without feedback of force or activation, as performed here, variations are likely greater than those found by Oskouei and Herzog (2005), as supported by the large standard deviations observed in the normalized data of Fig. 6.…”

“…Maximal voluntary contractions in human adductor pollicis under force and/or activation control have been associated with variations in force or activation of approximately 10% (Oskouei and Herzog 2005). For contractions performed without feedback of force or activation, as performed here, variations are likely greater than those found by Oskouei and Herzog (2005), as supported by the large standard deviations observed in the normalized data of Fig.…”

Is a parallel elastic element responsible for the enhancement of steady-state muscle force following active stretch?

“…Common tasks, such as locomotion, typically involve short periods of activation during which muscle length and velocity vary continuously; however, this does not mean that rFE cannot play a role in such tasks. It has been shown that rFE is present almost immediately after the end of stretch (Edman et al, 1984), that isotonic as well as isometric force is enhanced (Edman et al, 1978), and that rFE occurs in muscles that are voluntarily activated to submaximal levels (Oskouei and Herzog, 2005). Therefore, it seems likely that rFE influences muscle force during everyday activities.…”

Variation in isometric force after active shortening and lengthening and their mechanisms: a review

“…As in FD, the occurrence of FE initially was linked only to the lower limb and the peak of the LTC (22,23,24). However, new findings indicate that FE is also observed with reasonable stability in the ascending limb of the LCT (39,80,81,82).…”

“…stimulation combined with maximum voluntary dynamic contractions (5). Furthermore, devices have relied on complex servo motors coupled to force transducers that bear little resemblance to human movement pattern (2,11,14,15,16,17,18,19,20,21,22,23,24,25,26).…”