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The effect of the menstrual cycle on fluid balance during physical work in the heat when fluids are freely available is unknown. This study demonstrates that fluid balance is not modified in women across three distinct phases of the menstrual cycle during physical work in the heat These results indicate that when women have free access to cool fluid during physical work in the heat, they respond similarly across all three phases to maintain fluid homeostasis across the menstrual cycle.

Baranauskas, Marissa N., Timothy J. Fulton, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, and Robert F. Chapman. High intraindividual variability in the response of serum erythropoietin to multiple simulated altitude exposures.

Baranauskas, Marissa N., Joseph Powell, Alyce D. Fly, Bruce J. Martin, Timothy D. Mickleborough, Hunter L. Paris, and Robert F. Chapman. Influence of zinc on the acute changes in erythropoietin and proinflammatory cytokines with hypoxia.

INTRODUCTION: An adequate increase in minute ventilation to defend arterial oxyhemoglobin saturation (SpO(2)) during hypoxic exercise is commonly viewed as an important factor contributing to large inter-individual variations in the degree of exercise performance impairment in hypoxia. Although the hypoxic ventilatory response (HVR) could provide insight into the underpinnings of such impairments, it is typically measured at rest under isocapnic conditions. Thus, we aimed to determine whether 1) HVR at rest and during exercise are similar and 2) exercise HVR is related to the degree of impairment in cycling time trial (TT) performance from normoxia to acute hypoxia (ΔTT). METHODS: Sixteen endurance-trained men (V̇O(2peak), 62.5 ± 5.8 mL·kg(−1)·min(−1)) performed two poikilocapnic HVR tests: one during seated rest (HVR(REST)) and another during submaximal cycling (HVR(EX)). On two separate visits, subjects (n = 12) performed a 10-km cycling TT while breathing either room air (F(i)O(2) = 0.21) or hypoxic gas mixture (F(i)O(2) = 0.16) in a randomized order. RESULTS: HVR(EX) was significantly (P < 0.001) greater than HVR(REST) (1.52 ± 0.47 and 0.22 ± 0.13 L·min(−1)·%SpO(−1)(2), respectively), and these measures were not correlated (r = −0.16, P = 0.57). ΔTT was not correlated with HVR(REST) (P = 0.70) or HVR(EX) (P = 0.54), but differences in ventilation and end-tidal CO(2) between hypoxic and normoxic TT and the ventilatory equivalent for CO(2) during normoxic TT explained ~85% of the variance in performance impairment in acute hypoxia (P < 0.01). CONCLUSION: We conclude that 1) HVR is not an appropriate measure to predict the exercise ventilatory response or performance impairments in acute hypoxia and 2) an adequate and metabolically matched increase in exercise ventilation, but not the gain in the ventilatory response to hypoxia, is essential for mitigating hypoxia-induced impairments in endurance cycling performance.