Metabolic characteristics of skeletal muscle during detraining from competitive swimming

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Abstract
After 5 mo. of intense training 8 male swimmers were studied during 4 wk of inactivity. Biopsy specimens from the deltoid muscle revealed that its respiratory capacity (.ovrhdot.QO2) decreased by 50% (5174 to 2559 .mu.l .cntdot. h-1 g-1) after 1 wk of inactivity. Subsequent weeks of detraining did not change the .ovrhdot.QO2. Although the trained swimmers'' muscle phosphofructokinase and phosphorylase activities were significantly higher (P < 0.05) than those from a group (N = 8) of untrained men, four weeks of detraining had no effect on these enzyme activities. Mean (.+-. SE) resting muscle glycogen concentrations were significantly higher (P < 0.05) for the trained swimmers (153 .+-. 3 mmol .cntdot. kg-1) than for the untrained men (85 .+-. 7.5 mmol .cntdot. kg-1). Over the 4 wk of inactivity, the swimmers'' muscle glycogen progressively decreased from 153 (.+-. 3) to 93 (.+-. 7) mmol .cntdot. kg-1. After a standard 183-m swim at 90% of the swimmer''s best time for that distance, blood lactate rose from a mean of 4.2 (.+-. 0.8) at week 0 to 9.7 (.+-. 0.8) mmol .cntdot. l-1 at week 4. These observations demonstrate dramatic changes in the metabolic characteristics of the swimmer''s muscle with a 1-4-wk interruption in training.