Physiological and metabolic responses of late pregnant women to 40 min of steady-state exercise followed by an oral glucose tolerance perturbation

Abstract

We examined the physiological and metabolic responses of 24 active late pregnant women to 40 min of vigorous (95% ventilatory threshold) steady-state treadmill exercise followed by a metabolic perturbation [oral glucose tolerance test (OGTT), 75 g] after exercise. Heart rate and respiratory measures were taken throughout exercise, and blood samples were collected during exercise and every 30 min during the 2-h OGTT. Values were compared with those for a group of physically active nonpregnant women (n = 16) in the luteal phase of the menstrual cycle. Although late pregnant women were heavier, they performed the same work rate (182 vs. 208 W, P > 0.05), with the same oxygen pulse, but responded to the exercise with a blunted heart rate and relative oxygen consumption, with less carbon dioxide expired, possibly due to pregnancy-related adaptations in heart efficiency. Resting glucose concentrations were the same between groups, but by 40 min of exercise (3.8 ± 0.1 vs. 4.6 ± 0.1 mmol/l) and into 15 min of recovery (4.3 ± 0.2 vs. 5.0 ± 0.1 mmol/l), glucose concentrations were diminished in late pregnant women (P ≤ 0.05, respectively). The pregnancy-induced delay of glucose uptake was seen in response to the postexercise OGTT compared with the nonpregnant women, but insulin sensitivity (ISI) remained (7.4 ± 0.9 vs. 9.7 ± 1.4 ISI, P > 0.05, respectively), with the preservation of the sensitivity of lipolysis inhibition of nonesterified free fatty acids to insulin. These adaptations may be fetoprotective, because our research suggests that 40 min of continuous treadmill exercise is well tolerated by physically active pregnant women. No adverse effects on birth outcome (3.53 ± 0.08 kg birth weight; 39.6 ± 0.33 wk gestational age) were observed.

Maternal Responses to Aerobic Exercise in Pregnancy

“…However, as exercise intensity increases, reliance on glucose metabolism also increases and in pregnancy circulating glucose concentration may decline by up to 31% with increasing intensities. 6,[12][13][14][15][16][17] Less is known about the impact of duration of exercise on glucose metabolism in pregnancy. In nonpregnant females, circulating glucose initially declines in the first 20 minutes of exercise, followed by a return to preexercise levels with longer duration exercise as a result of liver glycogen breakdown/release or glycogenolysis.…”

“…18 However, pregnancy is associated with reduced liver glycogen storage, 19 thus maternal glucose concentrations may remain depressed withlongerdurationand/or higher intensity exercise. 16 Indeed, Soultanakis et al 17 examined the effect of 60 minutes of moderate intensity exercise and found that circulating glucose concentrations in pregnant women declined faster and reached lower levels than nonpregnant women. Mottola et al 16 also found that 40 minutes at 70% of VO 2max diminished glucose concentrations both during exercise and 15 minutes following cessation in late pregnant women compared with nonpregnant counterparts.…”

“…Mottola et al 16 also found that 40 minutes at 70% of VO 2max diminished glucose concentrations both during exercise and 15 minutes following cessation in late pregnant women compared with nonpregnant counterparts. Further, acute exercise is associated with a reduction in circulating insulin 16 suggesting that glucose is being utilized through insulin-independent pathways. However, insulin remains elevated in pregnant women compared with nonpregnant women during exercise, which may continue to promote glucose transfer to the fetus.…”

“…However, insulin remains elevated in pregnant women compared with nonpregnant women during exercise, which may continue to promote glucose transfer to the fetus. 16 The observation of improved glucose clearance and decreased hyperinsulinemia with acute (and chronic) exercise has been suggested to be a mechanism by which risk of developing gestational diabetes mellitus can be reduced.…”

“…Interestingly, although FFA levels are higher in pregnant compared with nonpregnant women atrest,duringexerciseinlatepregnancythe increase in circulating levels of triglycerides and FFAs are similar between groups at low-to-moderate exercise intensities. 7,12,13,16 Although the majority of studies suggest that exercise elevates circulating lipids, studies concurrently measuring blood lipids and the respiratory exchange ratio (a measure of lipid and carbohydrate metabolism) do not observe a change in respiratory exchange ratio suggesting that lipid production during prenatal exercise may not be used for energy production. Further investigation of these adaptations is warranted.…”