Myocellular triacylglycerol breakdown in females but not in males during exercise

The resting content and use of myocellular triacylglycerol (MCTG) during 90 min of submaximal exercise [60% of peak oxygen uptake ((V) over dotO(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 their (V) over dotO(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.