Effects of Pregnancy on Responses to Exercise Above and Below the Ventilatory Anaerobic THreshold

摘要

This research contract examined the effects of healthy human pregnancy on cardiac autonomic function (Study No. 1), oxygen uptake kinetics (Study No. 2)and acid-base regulation (Study No. 3) at rest and during upright cycling at intensities above and below the ventilatory anaerobic threshold (T to the vent). Results from Study No. 1 support the hypothesis that cardiac vagal/parasympathetic modulation is reduced in the resting state and that sympathoadrenal modulation is blunted during strenuous exercise above T to the vent in late gestation. These findings have important implications for the use of heart rate to regulate exercise intensity during pregnancy. Study No. 2 is still in progress. Findings from Study No. 3 demonstrated that plasma H+ is lower at rest and during exercise in the pregnant vs. nonpregnant state. Exercise-induced increases in H+ were similar quantitatively in the pregnant vs. nonpregnant state, but pregnant subjects have lesser reductions in the strong ion difference (SID) and require less respiratory compensation. Findings also suggested that plasma osmolality and SID contribute, in addition to circulating progesterone, to pregnancy-induced increases in pulmonary ventilation at rest and during exercise. Maximal exercise tests conducted as part of Studies No. 1 and No. 3 confirmed that maximal aerobic power and work efficiency are well-preserved in healthy physically active pregnant women and that such tests involve minimal changes in fetal heart rate.