THE EFFECTS OF SHORT-TERM VOLUNTARY IMMOBILIZATION ON THE CONTRACTILE PROPERTIES OF THE HUMAN TRICEPS SURAE

• Published in: Experimental physiology 1984-10, Vol.69 (4), p.685-691
• Main Authors: White, M. J., Davies, C. T. M., Brooksby, P.
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Anthropometry; Biological and medical sciences; Calcium - metabolism; Electric Stimulation; Evoked Potentials; Fundamental and applied biological sciences. Psychology; Humans; Immobilization; Isometric Contraction; Leg; Male; Muscle Contraction; Muscles - anatomy & histology; Sarcoplasmic Reticulum - metabolism; Space life sciences; Striated muscle. Tendons; Time Factors; Vertebrates: osteoarticular system, musculoskeletal system
• ISSN: 0958-0670; 0144-8757; 1469-445X
• DOI: 10.1113/expphysiol.1984.sp002860

In four male subjects one leg was immobilized in a full leg cast for 2 weeks. Measurements of the contractile properties of both triceps surae were made before, during and after immobilization. There was a significant increase in the mean twitch time to peak tension ( T c ) after 1 week of immobilization from 126 ± 10 ms to 143 ± 20 ms ( P 〈 0·05) and in the half-relaxation time ( T ½r ) from 88 ± 7 ms to 107 ± 12 ms ( P 〈 0·01). There were no further significant ( P 〈 0·1) changes in the twitch characteristics during the second week of immobilization. The strength of a maximal voluntary contraction (m.v.c.) declined by 11% ( P 〈 0·05) after 1 week and 24% ( P 〈 0·05) after 2 weeks. Twitch tension, tetanic tension and muscle fatigability were not significantly altered during immobilization. Muscle (plus bone) calf cross-sectional area ( A ) was reduced by 5% ( P 〈 0·01) after 1 week and a further 3% ( P 〈 0·05) after 2 weeks. The T c and T ½r of the twitch, m.v.c. and A returned to control values within 2, 7, 4 and 14 d respectively. No significant ( P 〉 0·01) changes were observed in the mechanical properties of the triceps surae of the contralateral limb during the period of immobilization. The results suggest that short-term voluntary immobilization is associated with atrophy and a diminished capacity of the muscle to develop maximal voluntary force. The increased contraction time of the twitch may indicate a change in the excitation-contraction coupling mechanism of the muscle and the disproportionate decrease in m.v.c. in relation to A and tetanic tension a reduction in the central neural drive.