Interrelationships between skeletal muscle adaptations and performance as studied by detraining and retraining

Abstract

The effects of 15 days of detraining and 15 days of retraining were studied in 6 well-trained runners. Detraining resulted in significant decreases in the mean activities of succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) of 24% and 13%, respectively, but no significant increases in these enzyme activities occurred with retraining. Maximal O2 uptake (.ovrhdot.VO2 max) decreased by 4% with detraining (P < 0.05), and increased by a similar amount with retraining. Performance time in an intense submaximal run decreased by 25% (P < 0.05) with inactivity, but still averaged 9% below the initial level after retraining.. Maximal heart rate and peak heart rate during the performance run were higher after detraining by 4 and 9 beats/min, respectively (P < 0.05). With retraining, these heart rate values were decreased by 7 and 9 beats/min (P < 0.05). Blood lactate concentrations after the .ovrhdot.VO2 max and performance run were approximately 20% lower after detraining and retraining (P < 0.05). Muscle fiber areas for 3 subjects tended to be larger in biopsy samples taken after detraining and retraining. Even short periods of detraining result in significant changes in indices of physiological capacity and function in subjects near their upper limit of adaptation, and a longer period of retraining is probably necessary for muscle to re-adapt to its original trained state.