- Title
- Sex differences in substrate utilisation during prolonged submaximal exercise
- Creator
- Brown, Wendy J.; White, Saxon William
- Relation
- 7th Commonwealth and International Conference on Sport, Physical Education, Recreation and Dance (Conference '82). Proceedings of the 7th Commonwealth and International Conference on Sport, Physical Education, Recreation and Dance, Volume 8 (Gold Coast, Qld 27-29 September, 1982) p. 143-150
- Publisher
- Dept. of Human Movement Studies, University of Queensland
- Resource Type
- conference paper
- Date
- 1983
- Description
- The observation that female marathon runners do not appear to 'hit the wall' like their male counterparts (when glycogen stores are depleted), has led to the suggestion that women may utilise a greater proportion for fat as energy substrate for endurance work than men (Ullyot, J. 1974. Runners World, December, 22-33). This study was designed to examine the metabolic status of male and female subjects, using respiratory exchange ration (R) as an index of substrate utilisation during submaximal steady, state endurance exercise. 31 healthy subjects were assigned to one of 5 groups, on the basis of sex, habitual physical training and measured V02 max. Each subject worked for 2 hours on a cycle ergometer at 50% of individual V02 max. There were thus no significant between-group differences in relative workload, but the trained subjects (groups 1, 2 and 4) worked at significantly higher absolute workload than the untrained subjects (groups 3 and 5) in order to achieve the same work level relative to their 'fitness'. Regression analysis of R on time for the different groups revealed the following: 1) at the onset of exercise females utilise a greater proportion of fat than males; 2) except in elite male athletes, training, in both sexes, tends to alter the energy substrate utilisation at the onset of exercise, in favour of greater fat metabolism; 3) during endurance exercise in all groups, the proportion of fat utilised increases significantly with time; 4) elite male athletes appear to be different in the sense that they utilise less fat at the onset of exercise than lesser trained subjects; however during endurance performance their substrate usage changes at a greater rate resulting in the utilisation of the same (or greater) proportion of fat as observed in the lesser trained subjects. It has been proposed that the capacity to utilise more fat in endurance performance may be a function of the carbohydrate sparing effects of female sex-hormones on intermediary metabolism. We have found high oestradiol levels in highly trained males (Brown, et al., 1980. Proc. Aust. Physiol. Pharmacol. Soc. 11, 131), and it is suggested that all highly trained athletes 'reset' their hormonal systems to facilitate the utilisation of fat as an energy source during endurance performance. 'Hitting the wall' in males, therefore, may be a mismatch between the induction of rapid carbohydrate utilisation at the beginning of exercise, and the facilitation of fat utilisation which may be dependent on high circulation levels of sex hormones, of which oestradial could play a highly significant role.
- Subject
- metabolic status; energy substrate utilisation; endurance work; men; women; oestradial
- Identifier
- http://hdl.handle.net/1959.13/938759
- Identifier
- uon:12672
- Identifier
- ISBN:0867761318
- Language
- eng
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