EXERCISE TRAINING FAILS TO PREVENT GLUCOCORTICOID-INDUCED MUSCLE ALTERATIONS IN YOUNG GROWING RATS

The aim of this study was to determine the impact of chronic treatment for 8 weeks with hydrocortisone acetate (5 mg kg-1 day-1) on skeletal muscles, and to evaluate whether sprint training can prevent glucocor ticoid-induced muscle atrophy better than endurance training. Biochemi cal, histological and contractile properties were employed to determin e the influence of this steroid on skeletal musculature, and the resul ts were compared to pair-weight animals to take into account the influ ence of corticoids on growth rate. It was found that hydrocortisone ac etate treatment results in a stunted growth, adrenal atrophy and depre ssed plasma corticosterone levels. Mild corticoid-induced losses of mu scle mass and protein content (9%-13%) were observed in fast-twitch sk eletal muscles. It appeared that the impact of corticoids is strictly directed toward type IIb fibres, which displayed a 12%-18% reduction i n cross-sectional areas. No alterations occurred in plantaris contract ile speed or tensions properties. Neither endurance training (30 m/min ; 90 min/day; 5 days/week) nor sprint training (60 m/min; 15 min/day; 5 days/week) for 8 weeks was able to counteract the effects of cortico ids. These data suggest that increased contractile activity, as induce d by treadmill running, is not sufficient to counteract the muscular e ffects of glucocorticoids when administered at a dose of 5 mg kg-1 day -1.