No Difference In Substrate Utilisation At Given Exercise Intensities Between Males And Females

Abstract

There is evidence that the relative number of slow muscle fibres is higher in women than in men. Fibre composition affects glycolysis, blood lactate concentration (BLC), aerobic carbohydrate and fatty acid combustion (CHO and FAO). It has been suggested that women use less CHO and more FAO at given exercise intensities. PURPOSE: To analyze potential differences in BLC and relative CHO (relCHO) between males and females. METHODS: 15 males (age: 24.5 ± 3.2 yrs, height: 179.9 ± 7.4 cm, weight: 77.1 ± 6.9 kg) and 14 females (22.4 ± 4.5 yrs, 163.3 ± 3.8 cm, 58.9 ± 7.5 kg) performed an incremental cycling test at a pedalling rate of 65 rpm. Exercise intensity was calculated as fraction of power output at test termination. BLC, oxygen uptake and carbon dioxide production were measured. CHO was determined using indirect calorimetry. relCHO was calculated as a fraction of the theoretical maximum CHO for a given oxygen uptake assuming a respiratory exchange ratio of 1.0. relCHO was described as a function of BLC. A constant that functionally represents the half-maximal activation of relCHO (kel) was approximated: relCHO = 100/(1 + kel/BLC2). RESULTS: There was a significant main effect of intensity (P < 0.05) on BLC and relCHO. No main effects of gender on BLC or relCHO nor any interactions between intensity and gender were found. kel (1.75 + 0.88 vs. 1.92 + 1.19; P > 0.05) was not different between males and females. CONCLUSION: The present study does not confirm differences in relCHO at given exercise intensities between males and females. Furthermore, the interrelation between BLC and relCHO was unaffected by gender.