CARBOHYDRATE LOADING AND METABOLISM DURING EXERCISE IN MEN AND WOMEN

During endurance exercise at similar to 65% maximal O-2 consumption, women oxidize more lipids, and therefore decrease carbohydrate and protein oxidation, compared with men (L. J. Tarnopolsky, M. A. Tarnopolsky, S. A. Atkinson, and J. D. MacDougall. J. Appl. Physiol. 68: 302-308, 1990; S. M. Phillips, S. A. Atkinson, M. A. Tarnopolsky, and J. D. MacDougall. J. Appl. Physiol. 75: 2134-2141, 1993). The main purpose of this study was to examine the ability of similarly trained male (n = 7) and female (n = 8) endurance athletes to increase muscle glycogen concentrations in response to an increase in dietary carbohydrate from 55-60 to 75% of energy intake for a period of 4 days (carbohydrate loading). In addition, we sought to examine whether gender differences existed in metabolism during submaximal endurance cycling at 75% peak O-2 consumption (VO2 peak) for 60 min. The men increased muscle glycogen concentration by 41% in response to the dietary manipulation and had a corresponding increase in performance time during an 85% VO2 peak trial (45%), whereas the women did not increase glycogen concentration (0%) or performance time (5%). The women oxidized significantly more lipid and less carbohydrate and protein compared with the men during exercise at 75% VO2 peak. We conclude that women did not increase muscle glycogen in response to the 4-day regimen of carbohydrate loading described. In addition, these data support previous observations of greater lipid and lower carbohydrate and protein oxidation by women vs. men during submaximal endurance exercise.