<p> While several investigations have reported a higher proportion of lipid oxidation (lower carbohydrate oxidation) in females performing heavy endurance exercise at the same relative intensity as males, some studies have failed to support this. Possible factors contributing to the lack of agreement may be differences in subject training status and diet, or the hormonal status of female subjects related to menstrual phase. All these variables are known to affect substrate metabolism during submaximal exercise. These factors were controlled in the present study by selecting subjects who were matched for level of physical conditioning and performance experience and placing them on eucaloric identical diets for 3 days. The females were tested during the mid-follicular phase of their menstrual cycle. Six males and 6 females ran on a treadmill at 65% VO2 max for a total distance of 15.5 km (range in performance times, 90 to 101 min). Pre and post exercise needle biopsies of vastus lateralis were assayed for glycogen concentration. Plasma glycerol, glucose, free fatty acids and selected hormones (catecholamines, growth hormone, insulin and glucagon) were measured throughout and following the run by sampling from an indwelling venous catheter. Exercise protein catabolism was estimated from 24 hr (resting and exercise) urinary urea N excretion. </p> <p> Males were found to have significantly higher respiratory exchange ratios (X =0.94 vs 0.87), greater muscle glycogen utilization (by 25%) and greater urea nitrogen excretion (by 30%) than females. Changes in selected hormone concentrations could not explain the greater lipid utilization observed in females. The lower insulin and higher epinephrine levels seen in males could in part explain the greater glycogenolysis and protein catabolism observed inn this group. It is concluded that, during moderate intensity long duration exercise, females demonstrate greater lipid utilization and less carbohydrate and protein metabolism than equally trained and nourished males. </p> / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22525 |
| Date | 04 1900 |
| Creators | Tarnopolsky, Larissa |
| Contributors | MacDougall, J. D., Human Biodynamics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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