Cardiovascular and Hematological Responses to Postpartum Sprint Interval Training in Trained Females

INTRODUCTION: Female athletes, or those in arduous occupations, lack objective guidance on effective and safe rigorous training postpartum. We examined the effectiveness and tolerability of early postpartum sprint interval training (SIT) in healthy recreationally active to international-level female athletes. METHODS: Ten new mothers (7.9 ± 2.4 wk postpartum, parity 1.6 ± 0.7 children) completed postpartum laboratory testing preintervention (PP pre ) and postintervention (PP post ). We measured maximal oxygen consumption ( ; metabolic cart), peak cardiac output ( , inert gas rebreathing), blood volume (BV), plasma volume (PV), and hemoglobin mass (Hb mass , carbon monoxide rebreathing). Between visits, participants completed 6 wk of home-based thrice weekly progressive SIT at 130% of peak power output (PPO). RESULTS: No adverse events occurred, and 173/180 sessions were completed. Participants breastfed without difficulty throughout the study. (2.39 ± 0.35 vs 2.75 ± 0.28 L/min; P < 0.0001) and PPO (233 ± 26 vs 264 ± 23 watts; P < 0.0001) increased from PP pre to PP post , whereas remained stable (14.6 ± 1.9 vs 14.5 ± 2.0 L/min). Hb mass (611 ± 73 vs 629 ± 79 g), BV (4684 ± 592 vs 4863 ± 573 mL) and PV (2898 ± 416 vs 3005 ± 367 mL) did not increase significantly at PP post . CONCLUSIONS: As both and Hb mass remained stable the increased likely stems from other physiological adaptations. Additionally, variability in study entry time, combined with cardio-hematological transitions from pregnancy, could account for the nonsignificant changes in hematological and results. Breastfeeding may have influenced and PV. Six weeks of SIT rapidly improves cardiovascular fitness in previously trained women. Furthermore, in recreational and elite athletes, ergometer cycling SIT is well tolerated, can be started early postpartum, and does not impede breastfeeding.