Introduction: The ventilatory threshold (named as VT1) and the respiratory compensation point (named as VT2) describe prominent changes of metabolic demand and exercise intensity domains during an incremental exercise test.Methods: A novel computerized method based on the optimization method was developed for automatically determining VT1 and VT2 from expired air during a progressive maximal exercise test. A total of 109 peak cycle tests were performed by members of the US astronaut corps (74 males and 35 females). We compared the automatically determined VT1 and VT2 values against the visual subjective and independent analyses of three trained evaluators. We also characterized VT1 and VT2 and the respective absolute and relative work rates and distinguished differences between sexes.Results: The automated compared to the visual subjective values were analyzed for differences with t test, for agreement with Bland–Altman plots, and for equivalence with a two one-sided test approach. The results showed that the automated and visual subjective methods were statistically equivalent, and the proposed approach reliably determined VT1 and VT2 values. Females had lower absolute O2 uptake, work rate, and ventilation, and relative O2 uptake at VT1 and VT2 compared to men (p ≤ 0.04). VT1 and VT2 occurred at a greater relative percentage of their peak VO2 for females (67 and 88%) compared to males (55 and 74%; main effect for sex: p < 0.001). Overall, VT1 occurred at 58% of peak VO2, and VT2 occurred at 79% of peak VO2 (p < 0.0001).Conclusion: Improvements in determining of VT1 and VT2 by automated analysis are time efficient, valid, and comparable to subjective visual analysis and may provide valuable information in research and clinical practice as well as identifying exercise intensity domains of crewmembers in space.

Background: Hemoglobin mass (Hbmass) is important for athletes because it helps determine maximal aerobic power. This study examined how lean mass, iron deficiency (ID), and sex influence Hbmass in athletic and non-athletic groups. Methods: NCAA Division I student athletes (21 males, 75 females, altitude: 1,625 meters) were recruited from six athletic teams; 14 male and 12 female full-time students (non-varsity athletes) served as controls. Hbmass, body composition, and iron homeostasis parameters, including ferritin, soluble transferrin receptor (sTfR), hepcidin, erythroferrone, and 10 inflammatory cytokines, were measured 2-4 times across a competitive/training season. ID was defined as ferritin <25 ng/mL. Results: Hbmass was more closely related to lean mass (r2=0.90) than body mass (r2=0.69, p<0.01). Compared to females, males had 19.9% higher Hbmass relative to body mass (HbmassBM), but only 7.5% higher Hbmass relative to lean mass (HbmassLEAN; both p<0.001). Prevalence of ID was higher in females than males (47% vs. 9%, p<0.01), but did not vary between groups. HbmassLEAN was 5% lower in ID versus non-ID females; Hbmass relative to body mass (HbmassBM) was not different. ID was associated with lower hepcidin, elevated sTfR, and elevated erythroferrone, but not with differences in inflammatory cytokines. Conclusion: Hbmass varied significantly between athletic groups and across sex, but the majority of these differences are explained by differences in lean mass. ID was common in females and was associated with lower HbmassLEAN and hepcidin, but not with differences in HbmassBM or inflammatory cytokines. Hbmass relative to lean mass seems advantageous when monitoring iron deficiency.

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