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Cardiac output, hematological, and performance responses to physiological perturbations in healthy trained females

Females have historically been underrepresented in medical and life science research. More specifically, we lack understanding of cardiac output (Q) and blood volume (BV) regulation in females. Two major physiological perturbations which affect Q and BV are the postpartum period and chronic heat exposure. This is of relevance as the number of female professional athletes or workers in arduous occupations (e.g. military) returning to work following childbirth, or working in high ambient temperatures is increasing. This work aimed to measure the cardiovascular, hematological, and performance response to exercise training undertaken soon postpartum (n=10) and following 5-weeks of heat acclimation (n=11). Training interventions included six-weeks of home-based sprint-interval training (SIT) in the postpartum study, whereas the heat acclimation study utilised 5-weeks of homebased hyperthermic overdressing stationary cycling. Key methodologies included Q measurement using inert gas rebreathing and BV measurement with carbon monoxide rebreathing. We show that in previously trained females postpartum SIT is well tolerated and rapidly increases fitness as demonstrated by an increase in VO2max and peak power output. However, both Q and BV did not change in our postpartum participants. In our heat acclimation study Q, BV and VO2max remained stable despite hot and thermoneutral environment performance increasing. As such in early postpartum exercise training, the central component of VO2max is unchanged suggesting that the increase in VO2 stems from other factors. In addition, our data show that strenuous training undertaken soon postpartum rapidly increases fitness and is well tolerated. Our heat acclimation intervention did not change Q, BV, nor VO2max but increased exercise performance in both hot and thermoneutral conditions suggesting a combined effect of heat adaptation and enhanced efficiency. In all, our studies show that following major physiological perturbations, namely the postpartum period and chronic heat exposure, Q and BV remain stable thus providing novel insight into cardiovascular control in trained females. Our findings also demonstrate high ecological validity as shown by the success of recruiting our target population and the nearly flawless compliance to our homebased training intervention.