Sex Differences in Economy During a Two Hour Run

B. Glace, M. McHugh, A. Lazoglu, G. Gleim, FACSM

NISMAT, Lenox Hill Hospital, New York, NY.

Changes in running economy during prolonged exercise have been described in men, but not in women. We examined changes in economy during a 2 hour run in 8 men and 8 women. Peak oxygen consumption (VO2peak) and oxygen consumption at anaerobic threshold (O2AT) were determined. Subjects then ran at an intensity which elicited O2AT for 2 hours (68.7% vs 66.6% of VO2peak for men and women, p=0.5). Water was ingested at a rate of 0.5% of body weight each half hour. The temperature was maintained at 19.7oC and 20.6oC, for men and women respectively (NS). Oxygen uptake (O2) and respiratory exchange ratio (RER) was measured initially and at 2 hours. Body weight declined in the men (p=0.001), but not in the women (p=0.12). Men increased O2 by 4.8% (p=0.001), and women by 2.2% (p=0.10), during exercise. Comparisons between men and women are shown below +/- SEM:

Changes 0-2 Hours    Men          Women       P-value
Delta Heart Rate  6.75+/-1.7    8.75+/-1.6     0.41
Delta O2 (ml)     147.4+/-14    44.6+/-23      0.002
Delta RER       -.0008+/-.008 -.0156+/-.01     0.25

Ratings of Perceived Exertion did not differ between sexes. These observations in men have been reported elsewhere. The nonsignificant increase in O2 in women during prolonged exercise has not been previously documented and does not appear to be due to differences in substrate utilization, but may be related to their better maintenance of hydration.

Med Sci Sports Exerc 26(5):s 1007, 1994