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.

Eight healthy volunteers were fitted with a supportive knee brace (Push Brace 'Heavy') to one knee for a duration of four weeks wherein they were tested before, during and after the application to establish the effect of bracing on performance. The tests consisted of isokinetic strength measurement of knee flexion and extension, 60 meter dash, vertical jump height and a progressive horizontal treadmill test until exhaustion (Vmax) with determination of oxygen uptake, heart rate and plasma lactate concentration. Wearing the brace for one day, the performance indicators showed a decline compared with the test before application (base values). Sprint time was 4% longer (p less than 0.01) and Vmax 6% slower (p less than 0.01). Peak torque of knee flexion at 60 and 240 deg.sec-1 was 6% (p less than 0.05) respectively 9% (p less than 0.05) less. Peak extension torque at 60 deg.sec-1 was 9% less (p less than 0.05). While wearing the brace for four weeks, the test performances were practically identical to their base values. After removal of the brace, all test parameters were statistically similar to the base values. Heart rate at submaximal exercise levels was even lower (p less than 0.05). In conclusion, performance in sports with test-like exercise patterns is not affected by the brace tested. Bracing does not "weaken the knee" as it is widely believed in sports practice.

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Effects of application of a hinged cast-brace on thigh muscle strength and physical performance tests were studied in eight healthy volunteers. The cast-brace was applied to one leg for four weeks. The subjects were free to move around. The extra loading by the cast-brace was determined in a progressive uphill walk test on a treadmill with measurements of oxygen uptake, heart rate and plasma lactate concentration. Submaximal oxygen uptake in the uphill walk test was raised significantly (average 9%) on the day after application. After four weeks of cast-brace wearing the submaximal oxygen uptake in the uphill walk test had decreased, but remained elevated (average 4%) even one day after removal. Heart rate was significantly higher (average 7%) during cast application and after removal. Plasma lactate concentration, however, was not influenced. To investigate the effect of four weeks cast-bracing various performance tests to judge the thigh muscle function were taken before application and after removal. No significant changes in peak torque of knee flexion and extension, in physiologic variables at submaximal running pace during treadmill exercise, maximal running speed, 60 m dash, or in jump height were found. In conclusion, cast-bracing of a healthy knee for four weeks has no significant effects on physical performance after removal.