Objective: This study was undertaken to examine substrate utilization and hormonal responses to moderate intensity exercise in the same group of women across gestation.
Study design: Glucose, triglyceride, insulin, glucagon, cortisol, growth hormone, and blood urea nitrogen levels were measured in 12 women at rest and after exercise. Heart rate, oxygen uptake, and respiratory exchange ratio were measured at rest and during exercise. Urine urea nitrogen levels, urine volume, and creatinine levels were measured 24 hours before and after exercise. Each woman completed a 30-minute treadmill walk at 65% of her predicted maximal heart rate at the same time of day during the 22nd and 33rd weeks of gestation and at 14 weeks after delivery.
Results: There were no significant differences between exercise trials in oxygen uptake, respiratory exchange ratio, or heart rate. Pregnancy elevated resting triglyceride levels but lowered plasma glucose levels. Exercise during pregnancy caused a reduction in plasma glucose levels but elevated circulating triglyceride levels (P <.05). Resting levels of cortisol, growth hormone, and insulin were elevated during pregnancy compared with after delivery, but resting glucagon levels were not affected by pregnancy. Exercise caused circulating levels of cortisol, growth hormone, and glucagon to increase (P <.05). The exercise-induced change in the cortisol level was greater during pregnancy than that after delivery. The exercise-induced changes in growth hormone and glucagon levels were greatest after delivery compared with those during pregnancy (P <.05). Exercise reduced insulin levels (P <.05), with the greatest reduction at 33 weeks' gestation. There were no significant differences in urine urea nitrogen excretion as a result of exercise.
Conclusions: Certain substrate and hormonal responses to exercise are altered as pregnancy progresses. Quantitatively, protein appears to be a relatively unimportant fuel during a 30-minute bout of moderate intensity exercise in this group of women evaluated during pregnancy and after delivery. Furthermore, a 30-minute bout of moderate intensity exercise would not be expected to compromise fetal amino acid availability.