Sex Differences in VO2max and the Impact on Endurance-Exercise Performance

Abstract

It was not until 1984 that women were permitted to compete in the Olympic marathon. Today, more women than men participate in road racing in all distances except the marathon where participation is near equal. From the period of 1985 to 2004, the women's marathon record improved at a rate three times greater than men's. This has led many to question whether women are capable of surpassing men despite the fact that there remains a 10-12% performance gap in all distance events. The progressive developments in sports performance research and training, beginning with A.V. Hill's establishment of the concept of VO_2max, have allowed endurance athletes to continue performance feats previously thought to be impossible. However, even today women are significantly underrepresented in sports performance research. By focusing more research on the female physiology and sex differences between men and women, we can better define how women differ from men in adapting to training and potentially use this information to improve endurance-exercise performance in women. The male advantage in endurance-exercise performance has commonly been attributed to their higher VO_2max, even when expressed as mL/kg/min. It is widely known that oxygen delivery is the primary limiting factor in elite athletes when it comes to improving VO_2max, but little research has explored the sex differences in oxygen delivery. Thus, the purpose of this review is to highlight what is known about the sex differences in the physiological factors contributing to VO_2max, more specifically oxygen delivery, and the impacts on performance.

Keywords: athletic performance; exercise physiology; oxygen consumption; sex differences.

Figure 1

Reprinted with permission from Ref. [3]. 2017 The Physiological Society. History of world records in the marathon for men and women, modified slightly to show current world record times. The impact of changes in training and culture has helped with the steep improvement in women’s marathon record times through 2005. Physiological sex differences are primarily responsible for the gap that still exists between men’s and women’s times in all distances of individual endurance events, although cultural and training differences still exist.

Figure 2

Reprinted with permission from ref. [41]. 2007 Blackwell Publishing. Regulation of lung volumes in men and women during progressive exercise to exhaustion. The end-expiratory (EELV) and end-inspiratory (EILV) lung volumes are expressed as a % of forced vital capacity (FVC). Higher EILV and EELVs were seen in women during progressive exercise, indicating dynamic hyperinflation. * Significantly different from men (p < 0.05).

Figure 3

(a) Reprinted with permission from Ref. [49]. 2017 the American Physiological Society. Diffusion capacity, pulmonary blood volume, and membrane diffusing capacity responses to exercise, corrected for alveolar volume, in male and female subjects. No significant differences were found. (b) Reprinted with permission from Ref. [50]. 2004 The Physiological Society Arterial PO₂, saturation, PCO₂, and alveolar-arterial PO₂ difference at rest and during exercise in normoxia. Male and female subjects are matched for age, height, and VO_2max.

Figure 4

Reprinted with permission from ref. [62]. 2015 Elsevier Inc. Gender-associated relative difference in structural indexes using different scaling parameters. Allometric indexing to LBM significantly reduced differences between men and women. Data are presented for (A) LV mass, (B) LV end-diastolic volume, (C) left atrial volume, and (D) RV end-diastolic area. * significant difference between males and females (p < 0.05); ns is not significant.

Figure 5

Reprinted with permission from ref. [64]. 2015 the American Physiological Society. (A) effect of 1 year of endurance training on VO_2max indexed to baseline body mass in males and females, (B) effect of 1 year of endurance training on changes in LV mass measured by MRI scaled to base-line fat-free mass. Post hoc comparison with baseline (*), with baseline, month 3 (†), and with month 6 (‡) for p < 0.05 from linear mixed model.

Figure 6

Reprinted with permission from ref. [69]. 2010 American College of Sports Medicine. Data are from 490 subjects (male n = 314, closed symbols; female n = 176, open symbols). Endurance state is classified by VO_2max. The dashed lines indicate hemoglobin concentration as a function of blood volume and hemoglobin mass.

Figure 7

Reprinted with permission from ref. [86]. 2020 the American Physiological Society. Differences in total hemoglobin mass (A), hemoglobin mass relative to total body mass (B), and hemoglobin mass relative to lean mass (C). * Significantly higher than sex-matched control subjects; ** significantly higher than all other sex-matched groups; † significantly different from control and alpine; ‡ significantly lower than male subjects.