UTILIZATION OF SKELETAL-MUSCLE TRIACYLGLYCEROL DURING POSTEXERCISE RECOVERY IN HUMANS

The utilization of muscle triacylglycerols was studied during and afte r prolonged bicycle ergometer exercise to exhaustion in eight healthy young men. Two days before exercise and in the postexercise recovery p eriod, subjects were fed a carbohydrate-rich diet (65-70% of energy fr om carbohydrates). Exercise decreased muscle glycogen concentrations f rom 533 +/- 18 to 108 +/- LO mmol/kg dry wt, whereas muscle triacylgly cerol concentrations were unaffected (49 +/- 5 before vs. 49 +/- 8 mmo l/kg dry wt after exercise). During the first 18 h after exercise, mus cle glycogen concentrations were restored to 409 +/- 20 mmol/kg dry wt . In contrast, muscle triacylglycerol concentrations decreased (P < 0. 05) to a nadir of 38 +/- 5 mmol/kg dry wt, and muscle lipoprotein lipa se activity increased by 72% compared with values before exercise. Pul monary respiratory exchange ratio values of 0.80-0.82 indicated a rela tively high fractional lipid combustion despite the high carbohydrate intake. From 18 to 42 h of recovery, muscle glycogen synthesis was slo w and muscle triacylglycerol concentrations and lipoprotein lipase act ivity were restored to the preexercise values. It is concluded that mu scle triacylglycerol concentrations are not diminished during exhausti ve glycogen-depleting exercise. However, in the postexercise recovery period, muscle glycogen resynthesis has high metabolic priority, resul ting in postexercise lipid combustion despite a high carbohydrate inta ke. It is suggested that muscle triacylglycerols, and probably very lo w density lipoprotein triacylglycerols, are important in providing fue l for muscle metabolism in the postexercise recovery period.