Respiratory and metabolic responses to endurance cycle exercise in pregnant and postpartum women

This study was designed to determine whether endurance cycling responses in pregnancy differ from those postpartum. We studied 16 women longitudinally at approximately 32 wk pregnancy and approximately 10 wk postpartum. We measured heart rate (HR), O2 uptake (VO2), CO2 output (VCO2), minute ventilation VE and plasma concentrations of substrates and of catecholamines at rest, during maximal testing, and during approximately 35-40 min of cycling at approximately 70-75% VO2peak. Endurance exercise time and power were 37.6+/-1.0 min and 124+/-8 W in pregnancy, similar to values observed postpartum. HR and respiratory responses near the end of endurance exercise were also unaffected by gestation, with pregnancy values of 173+/-3 bpm, 1.87+/-0.07 L/min VO2, and 1.68+/-0.07 L/min VCO2, except that VE at 70.0+/-3.5 L/min was 14% higher than postpartum; plasma concentrations of free fatty acids (404+/-62 micromol/L), glucose (3.34+/-0.17 mmol/L), and lactic acid (4.51+/-0.50 mmol/L) were lower than postpartum by 9, 24, and 19%, respectively; catecholamine concentrations were not different from those determined postpartum. We conclude that pregnant women are equally capable as are postpartum women to perform approximately 40 min of cycling at 70-75% VO2peak, and that the physiologic responses to endurance exercise are largely independent of gestation.