Myocellular triacylglycerol breakdown in females but not in males during exercise

Abstract

The resting content and use of myocellular triacylglycerol (MCTG) during 90 min of submaximal exercise [60% of peak oxygen uptake (V˙o 2 peak)] were studied in 21 eumenorrheic female and 21 male subjects at different training levels [untrained (UT), moderately trained (MT), and endurance trained (END)]. Males and females were matched according to theirV˙o 2 peak expressed relative to lean body mass, physical activity level, and training history. All subjects ingested the same controlled diet for 8 days, and all females were tested in the midfollicular phase of the menstrual cycle. Resting MCTG, measured with the muscle biopsy technique, averaged 48.4 ± 4.2, 48.5 ± 8.4, and 52.2 ± 5.8 mmol/kg dry wt in UT, MT, and END females, respectively, and 34.1 ± 4.9, 31.6 ± 3.3, and 38.4 ± 3.0 mmol/kg dry wt in UT, MT, and END males, respectively ( P < 0.001, females vs. males in all groups). Exercise decreased MCTG content in the female subjects by an average of 25%, regardless of training status, whereas in the male groups MCTG content was unaffected by exercise. The arterial plasma insulin concentration was higher ( P < 0.05) and the arterial plasma epinephrine concentration was lower ( P < 0.05) in the females than in the males at rest and during exercise. MCTG use was correlated to the resting concentration of MCTG ( P < 0.001). We conclude that resting content and use of MCTG during exercise are related to gender and furthermore are independent of training status.