SIX WEEKS' AEROBIC RETRAINING AFTER TWO WEEKS' IMMOBILIZATION RESTORES LEG LEAN MASS AND AEROBIC CAPACITY BUT DOES NOT FULLY REHABILITATE LEG STRENGTH IN YOUNG AND OLDER MEN

Objective: To determine the effect of aerobic retraining as rehabilitation after short-term leg immobilization on leg strength, leg work capacity, leg lean mass, leg muscle fibre type composition and leg capillary supply, in young and older men. Subjects and design: Seventeen young (23 +/- 1 years) and 15 older (68 +/- 1 [standard error of the mean; SEMI years) men had one leg immobilized for 2 weeks, followed by 6 weeks' bicycle endurance retraining. Methods: Maximal voluntary contraction, leg work capacity (W-max), and leg lean mass by dual energy X-ray absorptiometry were measured at inclusion, after immobilization and after 3 and 6 weeks' retraining. Muscle biopsies were evaluated for fibre type, fibre area, and capillarization. Results: Immobilization decreased maximal voluntary contraction (-28 +/- 6% and -23 +/- 3%); W-max (-13 +/- 5% and -9 +/- 4%) and leg lean mass (only in young, -485 +/- 105g) in young and older men, respectively. Six weeks' retraining increased maximal voluntary contraction (34 +/- 8% and 17 +/- 6%), W-max. (33 +/- 5% and 20 +/- 5%) and leg lean mass (only in young 669 +/- 69 g) in young and older men, respectively, compared with the immobilized value. Conclusion: Short-term leg immobilization had marked effects on leg strength, and work capacity and 6 weeks' retraining was sufficient to increase, but not completely rehabilitate, muscle strength, and to rehabilitate aerobic work capacity and leg lean mass (in the young men).