The effects of short-term voluntary immobilization on the contractile properties of the human triceps surae.

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 (Tc) after 1 week of immobilization from 126 +/- 10 ms to 143 +/- 20 ms (P less than 0.05) and in the half-relaxation time (T1/2r) from 88 +/- 7 ms to 107 +/- 12 ms (P less than 0.01). There were no further significant (P less than 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 less than 0.05) after 1 week and 24% (P less than 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 less than 0.01) after 1 week and a further 3% (P less than 0.05) after 2 weeks. The Tc and T1/2r of the twitch, m.v.c. and A returned to control values within 2, 7, 4 and 14 d respectively. No significant (P less than 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.(ABSTRACT TRUNCATED AT 250 WORDS)