Alterations in contractile properties of human skeletal muscle induced by joint immobilization

Abstract

The effects of joint immobilization on the contractile properties of human skeletal muscle were examined using the first dorsal interosseous (FDI) muscle. The middle finger, index finger and thumb were immobilized for a period of 6 weeks, and the contractile properties of FDI were tested before immobilization, after 3 and 6 weeks of immobilization, and after a 6 week recovery period. Twitch and tetanic contractions of FDI were evoked by per‐cutaneous electrical stimulation. The peak twitch tension (Pt), contraction time (CT) and half‐relaxation time (1/2RT) were measured from twitch contractions, while the stimulus frequency‐force relationship was obtained from the tetanic contractions (2 s) evoked using various frequencies of stimulation (10‐100 Hz). The fatigability of FDI was tested using Burke's fatigue protocol. Pt was significantly increased after 6 weeks of immobilization (P < 0.05) but little alteration was observed in CT or 1/2RT. No change was noted in the FDI fatigue index throughout the immobilization period. The stimulus frequency‐force relationship was shifted to the left by immobilization, indicating that a larger percentage of maximal force was evoked by the lower rates of stimulation. Indeed, the tetanic force evoked by a stimulus frequency of 10 Hz was enhanced after immobilization (P < 0.05). On the other hand, the force evoked by frequencies above 50 Hz, including maximal tetanic tension, was decreased (P < 0.05). As a result, the twitch/tetanus ratio was increased (P < 0.01) after immobilization. The changes induced by immobilization in the FDI twitch/tetanus ratio and the estimated maximal firing rate of FDI motoneurones showed a significant correlation (r= 0.80, P < 0.05). It is suggested that the changes in the contractile properties of the FDI muscle seen after joint immobilization are causally linked to the changes in firing rate modulation of FDI motoneurones.

Modulation of motor cortex excitability after upper limb immobilization

“…This finding, which is likely to be related to disuse atrophy, is in accordance with previous experimental reports of skeletal muscle changes after upper-limb immobilization (Desaphy et al, 2001;Seki et al 2001a;2001b).…”

“…Animal studies suggest that sensory impoverishment may determine changes in the organization and size of cortical receptive fields in the somatosensory cortex (Coq and Xerri, 1999;Langlet et al, 1999). The vast majority of studies on the effects of long term immobilization in humans have examined changes in the contractile properties of skeletal muscle (Desaphy et al, 2001;Seki et al, 2001b) or motor units (Seki et al, 2001a). Only two reports to date have documented central motor changes in neurologically normal subjects who wore splints for more than four weeks because of fractures of the wrist (Zanette et al, 1997) or the leg (Liepert et al, 1995).…”

Influence of subcutaneous fat on mechanomyographic signals at three levels of voluntary effort

“…The MMG signals originated in the skeletal muscle come from the mechanical vibrations generated by the muscular shocks of the APs (Yoshitake et al, 2002), which combined with MUs lead to MVC (tetany) (Neering et al, 1991;Seki et al, 2001). In this study, the thicker layers of body fat increased the distance between sensor and muscle, and the physical aspects of the fat acted as a low-pass filter, attenuating the MMG signal, as demonstrated by the analyzed parameters.…”

Short-Term Limb Immobilization Affects Motor Performance

“…The first studies were conducted on participants who wore splints either at the upper limb or the lower limb for 4−6 weeks because of fractures (Kaneko, Murakami, Onari, Kurumadani, & Kawaguchi, 2003;Liepert, Tegenthoff, & Malin, 1995;Seki, Taniguchi, & Narusawa, 2001a, 2001b. Long-term joint immobilization is known to modify the proportion of fast and slow muscle fibers and thus the contractility of skeletal muscle (Bey et al, 2003;Seki et al, 2001a) and perhaps to change the intrinsic properties of motor neurons and the input to motor neurons from peripheral afferents (Seki et al, 2001b). Although the results of some electrophysiological studies have suggested that changes of neural excitability at both central and peripheral levels may occur only after weeks or even months of immobilization, immobilization indeed induces modification of the sensorimotor input and motor behavior as soon as the cast is applied.…”