SUBSTRATE AND ENDOCRINE RESPONSES DURING EXERCISE AT SELECTED STAGES OF PREGNANCY

To determine whether the concomitant effects of pregnancy and exercise yield substrate and endocrine patterns different from those expected during exercise alone, we compared the responses of glucose, lactate, free fatty acids, insulin, epinephrine (EP), norepinephrine (NE), human chorionic gonadotropin (HCG), human placental lactogen (HPL), estriol, and progesterone (P) in nonpregnant women (NP; n = 7) and pregnant women in the second (TR2; n = 6) and third trimester (TR3; n = 8) of pregnancy, before, during, and after 30 min of bicycle ergometer exercise at heart rates of 130-140 beats/min. In general, all substrates and hormone concentrations increased with exercise (P < 0.05), except insulin, which decreased (P < 0.05), and HCG, which did not change (P = 0.08). Differences in selected hormone concentrations (P, estriol, HCG, and HPL) among groups were already present at rest because of the different stages of pregnancy. Differences among groups at rest were also found in insulin and NE (P < 0.05). Significantly different responses to exercise (i.e., group X time interactions) were as follows. NP vs. TR2: P, estriol, HCG, HPL, EP, and NE (P < 0.05); NP vs. TR3: glucose, EP, and NE (P < 0.05); TR2 vs. TR3: lactate, EP, and NE (P < 0.05). It was especially noteworthy that 1) the substrate and hormonal changes were, however, quite transient; in most instances, preexercise concentrations were reestablished within 30 min after exercise, 2) no changes in fetal heart rates occurred (P > 0.05) despite the increments in exercise-induced maternal heart rates (P < 0.05), and 3) the women in TR2 and TR3 experienced glucose decrements of 25 and 32% that were significantly greater (P < 0.05) than the 16% decrement in the control group. Therefore, although exercise does not provoke anomalous endocrine responses in pregnant women, the large glucose decrease during exercise in TR2 and TR3 may require caution.