BACKGROUND: Circulating blood volume (BV) and maximal oxygen uptake (Vo2max) are physiological characteristics important for optimal human performance in aerospace and military operational environments. We tested the hypothesis that BV and Vo2max are lower in older people independent of sex.METHODS: To accomplish this, a "data mining" effort of an historic database generated from NASA and U.S. Air Force experiments was conducted. BV, red cell volume, plasma volume, hematocrit, and Vo2max were measured in 84 healthy individuals (24 women, 60 men) across an age range of 23 to 65 yr to assess the interrelationship between sex, age, BV, and Vo2max. Subjects were classified in age groups by < 40 yr and ≥ 40 yr; these groups identified women as pre- vs. postmenopausal.RESULTS: Consistent with our hypothesis, comparisons revealed that men had higher BV, red cell volume, hematocrit, and Vo2max than women when standardized for body mass. Against expectations, BV was not different in older compared with younger men and women. Vo2max was not different in older compared with younger women, while Vo2max was lower in older men.CONCLUSION: We conclude that physiological mechanisms other than BV associated with aging appear to be responsible for a decline in Vo2max of our older men. Furthermore, factors other than menopause may also influence the control of BV in the women. Our results provide evidence that aging may not compromise men or women in scenarios where BV can affect performance in aerospace and military environments.Koons NJ, Suresh MR, Schlotman TE, Convertino VA. Interrelationship between sex, age, blood volume, and Vo2max. Aerosp Med Hum Perform. 2019; 90(4):362-368.