Functional and morphological adaptations following four weeks of knee immobilization

Immobilization of the knee as part of the treatment in bone or joint lesions leads to atrophy and consequently loss of functionally. In patients this atrophy and loss of functionality is difficult to quantify because of interfering symptoms and missing baseline data. In the present study structural and functional changes in thigh muscles were examined in eight healthy volunteers of whom one leg was immobilized in a cast for four weeks. Quadriceps cross-sectional area determined with computed tomography was 21% +/- 7% diminished after four weeks immobilization (p < 0.05). Muscle biopsies from the musculus vastus lateralis revealed an 16% decreased fiber diameter (p < 0.05) and no significant shift in fiber types. Isokinetic strength measurements of knee extensors and flexors demonstrated a fall in peak torque of 53% +/- 9% and 26% +/- 13% at an angular velocity of 60 deg.s-1 (p < 0.01). Aerobic power in one-leg-cycling exercise was not significantly affected, but isokinetic quadriceps endurance work decreased from 9.1 kJ to 5.6 kJ (p < 0.05). Despite the fall in quadriceps performance the subjects had only minor functional complaints for a few days. It is concluded that immobilization of the knee is an important factor in the development of thigh muscle atrophy in patients and should therefore be diminished as much as possible.