Gender differences in substrate for endurance exercise

Abstract

The effects of gender on substrate utilization during prolonged submaximal exercise were studied in six males and six equally trained females. After 3 days on a controlled diet (so that the proportions of carbohydrate, protein, and fat were identical), subjects ran on a treadmill at a velocity requiring an O2 consumption of approximately 65% of maximal. They ran a total "distance" of 15.5 km with a range in performance time of 90-101 min. Plasma glycerol, glucose, free fatty acids, and selected hormones (catecholamines, growth hormone, insulin, and glucagon) were measured throughout and after the run by sampling from an indwelling venous catheter, and glycogen utilization was calculated from pre- and postexercise needle biopsies of vastus lateralis. Exercise protein catabolism was estimated from 24-h urinary urea nitrogen excretion over the test day and a nonexercise day. The males were found to have significantly higher respiratory exchange ratios (mean 0.94 vs. 0.87), greater muscle glycogen utilization (by 25%), and greater urea nitrogen excretion (by 30%) than the females. No gender differences were evident in the hormonal response to the exercise with the exception of a lower insulin concentration and a higher epinephrine concentration in the males. We conclude that, during moderate-intensity long-duration exercise, females demonstrate greater lipid utilization and less carbohydrate and protein metabolism than equally trained and nourished males.

The beneficial effects of body fat and adipose tissue in humans*

“…There are reports that women, with their greater adipose tissue masses, have lower RERs in exercise than men 52 and in this respect they resemble trained individuals. However, because of the great heterogeneity of protocols adopted and subjects investigated there is still some doubt about sex differences in substrate utilisation during exercise.…”

Metabolismo energético em atletas de endurance é diferente entre os sexos

“…Alguns autores afirmaram que as concentrações basais de glicogênio muscular são similares em homens e em mulheres 1,2,6,20 , entretanto, estudos sugerem diferenças entre os sexos na utilização do glicogênio hepático e não do glicogênio muscular esquelético 2,6,12,16,21 .…”

“…Além desse, outros hormônios vêm sendo citados como possíveis mediadores, como: progesterona, testosterona, catecolaminas (epinefrina e norepinefrina), hormô-nio de crescimento, insulina e glucagon 1,4,13,25,28 . O ciclo menstrual parece influenciar a utilização de carboidratos nas mulheres durante o exercício 29 , mas não altera o metabolismo de lipídeos 30 .…”

“…Durante o exercício de endurance, alguns autores encontraram maiores concentrações de catecolaminas nos homens 1,4,13,25,28 enquanto que nas mulheres a insulina estava em maior quantidade 1,13 . Porém, outros não encontraram diferenças entre os sexos nas concentrações desses hormônios 3,12 .…”

Evaluation of gender differences in physiology: an introduction

“…Another critical factor to consider in gender comparative studies is the phase of the menstrual cycle and (1985) [35] 6 F, T 90 min walk @ 35% VO 2max F = 0.81 6 M, T M = 0.85 Tarnopolsky et al (1990) [22] 6 F, T 15.5 km run @ *65% VO 2max F = 0.876 6 M, T M = 0.940 Phillips et al (1993) [21] 6 F, T 90 min cycle @ 65% VO 2max F = 0.820 6 M, T M = 0.853 Tarnopolsky et al (1995) [23] 8 whether or not the females are having regular menses (eumenorrhea) versus amenorrhea or oligoamenorrhea. During the follicular phase of the menstrual cycle (approximately the ®rst 14 days after the onset of menses) the estradiol concentration starts at levels comparable to males and then increases until ovulation (which marks the onset of the luteal phase).…”