MAXIMAL AEROBIC EXERCISE IN PREGNANT-WOMEN - HEART-RATE, O2 CONSUMPTION, CO2 PRODUCTION, AND VENTILATION

This study was to determine whether pregnancy affects maximal aerobic power. We measured heart rate, O2 uptake (VO2), CO2 production (VCO2), and ventilation at rest and during bicycle (BE) and treadmill exercise (TE) tests with rapidly increasing exercise intensities at 16, 25, and 35 wk gestation and 7 wk after delivery. Maximal heart rate was slightly lower throughout pregnancy compared with the nonpregnant state during both BE [174 +/- 2 vs. 178 +/- 2 (SE) beats/min] and TE (178 +/- 2 vs. 183 +/- 2 beats/min). Maximal Vo2 was unaffected by pregnancy during BE and TE (2.20 +/- 0.08, 2.16 +/- 0.08, 2.15 +/- 0.08, and 2.19 +/- 0.08 l/min for BE and 2.45 +/- 0.08, 2.38 +/- 0.09, 2.33 +/- 0.09, and 2.39 +/- 0.08 l/min for TE at 16, 25, and 35 wk gestation and 7 wk postpartum, respectively). As a result of increased Vo2 at rest, the amount of O2 available for exercise (exercise minus rest) tended to decrease with advancing gestation, reaching statistical significance only during TE at 35 wk gestation (1.99 +/- 0.08 l/min vs. 2.10 +/- 0.08 l/min postpartum). Power showed a positive linear correlation with O2 availability during BE as well as TE, and the relationship was unaffected by pregnancy. VCO2 at maximal exercise was lower during pregnancy than at 7 wk postpartum (2.56 +/- 0.09, 2.51 +/- 0.08, 2.46 +/- 0.09, and 2.70 +/- 0.09 l/min for BE and 2.72 +/- 0.09, 2.66 +/- 0.09, 2.55 +/- 0.09, and 2.79 +/- 0.08 l/min for TE at 16, 25, and 35 wk gestation and postpartum, respectively), whereas maximal ventilation was increased during gestation (95.6 +/- 3.2, 94.6 +/- 2.9, 96.1 +/- 3.5, and 89.5 +/- 3.0 l/min for BE and 98.8 +/- 2.6, 99.6 +/- 3.3, 98.1 +/- 3.0, and 91.7 +/- 2.6 l/min for TE at 16, 25, and 35 wk gestation and postpartum, respectively). Except for the hyperventilation of pregnancy, which was maintained at maximal aerobic exercise, the relationship between ventilation and VCO2 (or VO2) was unaffected by gestation. We conclude that pregnancy does not have a marked effect on maximal aerobic power.