A number of studies have examined the influence of gender/sex on metabolic fuel selection during endurance activity.40,41,64,67,74,75,138-140 Overall, women appear to oxidize proportionately more lipid and less CHO than men during endurance exer-cise.40'41'64'67'74'75'138-140 The lower contribution from CHO in exercising females would imply that amino acid oxidation should also be lower than in men. In an earlier study using 24-h urinary urea excretion as a marker of total amino acid oxidation, we found that men, but not women, showed elevated 24-h urinary urea during a day in which they completed a 15.5-km treadmill run as compared to a rest day.64 Using leucine as a stable isotope tracer, our group41 and others67141 found that women oxidized proportionately less leucine than men during endurance cycling. The reduced leucine oxidation observed for women during endurance exercise is apparent prior to and following 31 days of endurance exercise training.40 In the latter study we did not find that the gender difference could be explained based upon either the total or active proportion of skeletal muscle BCOAD.40 This finding suggests that the locus of the gender difference in amino acid oxidation cannot be explained at the skeletal muscle level, and may be at the hepatic level. To further uncover the mechanisms involved in gender-related differences in protein metabolism during exercise, we supplemented healthy men with the sex hormone estrogen. Following 8 days of supplementation, the men demonstrated a reduced dependence on amino acids and CHO and an increased reliance on lipids as a fuel source during endurance exercise.142 A summary of the effects of exercise on protein metabolism in men and women is found in Table 7.1.
Was this article helpful?
Buying a treadmill is hard enough. Choosing the best out of many treadmills in the market is nigh impossible. But once youve got the treadmill youve always wanted, are your worries truly over? Well, they certainly are, but only if you maintain your treadmill properly.