Effects of pregnancy on maternal work tolerance.

This review summarizes current information on the tolerance of healthy pregnant women and their fetuses to acute strenuous exertion. Maximal aerobic power, expressed in L x min(-1), is not significantly affected in women who maintain an active lifestyle, whereas values expressed in ml x kg(-1) x min(-1) decline with advancing gestational age in relation to maternal/fetal weight gain. Efficiency during standard exercise testing and the ventilatory anaerobic threshold (Tvent) also appear to be unaffected by pregnancy, but the ability to utilize carbohydrate and exercise anaerobically during brief strenuous exercise may be reduced. Fetal responses to short strenuous exercise are usually moderate and revert to baseline values within approximately 30 min postexercise. Future studies should examine alveolar gas exchange kinetics at the start of exercise and during recovery from both moderate and strenuous exertion. Existing studies of the responses of pregnant women to prolonged exercise have focused primarily on substrate utilization and glucose homeostasis. Other maternal responses to prolonged exercise that should be examined include acid-base regulation, temperature regulation, fluid and electrolyte balance, and perception of effort. Fetal reactions should also be examined in relation to maternal responses. Until evidence-based, occupation-specific guidelines become available, it is recommended that pregnant women use the Joint SOGC/CSEP Clinical Practice Guideline: Exercise in Pregnancy and the Postpartum Period, published by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology (2003).