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

• Published in: The Journal of physiology Vol. 530; no. 3; pp. 521 - 532
• Main Authors: Seki, Kazuhiko, Taniguchi, Yuko, Narusawa, Mitsuo
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01-02-2001; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: Adult; Electric Stimulation; Fingers; Humans; Immobilization - physiology; Joints - physiology; Male; Muscle Contraction - physiology; Muscle Fatigue - physiology; Muscle, Skeletal - physiology; Original; Time Factors
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.2001.0521k.x

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.