Effect of exercise intensity and duration on capillary glucose responses in pregnant women at low and high risk for gestational diabetes.

BACKGROUND: Exercise may influence glucose metabolism during pregnancy. We examined the effect of exercise intensity and duration on capillary glucose responses in pregnant women at low and high risk for gestational diabetes mellitus (GDM) who followed a modified GDM meal plan. METHODS: Randomization occurred at study entry (16-20 weeks' gestation) into a low-intensity [30% heart rate reserve, low risk-30%I, n = 12; high risk-30%I, n = 11] or vigorous-intensity (70% heart rate reserve, low risk-70%I, n = 12; R-70%I, n = 11) exercise program with similar nutritional control. Exercise consisted of walking three to four times a week, gradually increasing time from 25 to 40 min/session. Free-living capillary glucose concentrations were measured once a week pre-exercise and post-exercise. RESULTS: Capillary glucose responses to exercise were strongly influenced by an interaction between GDM risk, exercise duration and exercise intensity (p = 0.006). Decreases in glucose concentrations were observed after 25 (4 ± 13%), 35 (21 ± 12%) and 40 min (15 ± 18%) of walking in high risk-30%I women, with the most noticeable decline after 35 and 40 min. In the high risk-70%I, glucose concentrations decreased significantly only after 25 (22 ± 14%) and 35 min (7 ± 23%) and increasing the exercise time attenuated glucose concentrations decline. In low risk women, regardless of exercise intensity and duration, decreases in glucose concentrations were significant and similar. CONCLUSION: To achieve the best decline in glucose concentrations, pregnant women who follow a modified GDM meal plan should walk for 25 min/session at vigorous intensity or for 35-40 min/session at low intensity if they are at risk for GDM and for at least 25 min at either low or vigorous intensity if they are at low risk for GDM.

Effects of maternal exercise on liver and skeletal muscle glycogen storage in pregnant rats.

To examine the effects of maternal exercise on liver and skeletal muscle glycogen storage, female Sprague-Dawley rats were randomly divided into control, nonpregnant runner, pregnant nonrunning control, pregnant runner, and prepregnant exercised control groups. The exercise consisted of treadmill running at 30 m/min on a 10 degree incline for 60 min, 5 days/wk. Pregnancy alone, on day 20 of gestation, decreased maternal liver glycogen content and increased red and white gastrocnemius muscle glycogen storage above control values (P less than 0.05). In contrast, exercise in nonpregnant animals augmented liver glycogen storage and also increased red and white gastrocnemius glycogen content (P less than 0.05). By combining exercise and pregnancy, the decrease in liver glycogen storage in the pregnant nonexercised condition was prevented in the pregnant runner group and more glycogen was stored in both the red and white portions of the gastrocnemius than all other groups (P less than 0.05). Fetal body weight was greatest (P less than 0.05) in the pregnant runner group and lowest (P less than 0.05) in the prepregnant exercise control group. These results demonstrate that chronic maternal exercise may change maternal glycogen storage patterns in the liver and skeletal muscle with some alteration in fetal outcome.

The use of animal models in exercise and pregnancy research.

This article will discuss the use of animal models in exercise and pregnancy research. Although the ultimate goal is understanding mechanisms of change as a result of maternal exercise as they apply to pregnant women and the fetus, animal models deserve a place in research because of ethical constraints placed on experimentation on pregnant women. The risk identified through animal research should not be ignored if safe exercise guidelines are to be recommended to women who wish to engage in exercise during pregnancy.

Training effects on maternal and fetal glucose uptake following acute exercise in the rat.

The purpose of the present study was to determine the effects of chronic maternal exercise on glucose uptake in maternal tissues after one bout of treadmill running during late gestation in the rat and to determine the effects on glucose accumulation in the fetus and placenta. Trained pregnant animals (PR) ran at 30 m.min-1, on a 10 degrees incline for 1 h on day 20 of gestation with a similarly treated trained nonpregnant group (NPR). Immediately after the run the animals were infused with a bolus of 1 g.kg-1 body wt as a 50% dextrose solution mixed with 2-deoxy-D-[1-3H] glucose through a carotid catheter. Sedentary pregnant (P) and nonpregnant animals (C) were also infused with the solution after no food and water for the same time frame. After 60 min, tissues were analyzed for radioactivity. Radioactive tracer was augmented in the red gastrocnemius and soleus of the PR group and the soleus of P rats. However, tracer accumulation in the fetus and placenta of the trained animals was not different than P animals. These results indicate that acute exercise in trained animals increased glucose uptake in maternal skeletal muscles without compromising conceptus glucose accumulation.

Recent advances in understanding maternal and fetal responses to exercise.

In the past decade, physical health fitness has become increasingly more important in the lives of women of child-bearing age. Many have made regular, and sometimes vigorous commitments to exercise programs. In 1985, the American College of Obstetricians and Gynecologists (ACOG) developed a set of guidelines for women who plan to exercise during pregnancy. Recommendations were based on available, but somewhat limited, scientific data and common sense. Since that time, researchers have learned a significant amount of new information about how a pregnant woman and her fetus respond to aerobic activity. The objective of this communication is to review recent investigations in this area. Specific topics include a) maternal responses to exercise, b) fetal responses to maternal exercise, c) animal research models, and d) pregnancy and physical conditioning. Our objectives are to present information that will a) stimulate new and innovative research designs for exercise and pregnancy studies, and b) add significantly to our knowledge and ability to develop safe and effective exercise programs for women who wish to remain physically active throughout a normal-term pregnancy.

Biomechanical Factors Affecting Dave Dravecky's Return to Competitive Pitching: A Case Study.

Dave Dravecky, pitcher for the San Francisco Giants, returned to competition 10 months after surgical removal of a desmoid tumor in the deltoid muscle and cryosurgery of the humerus of his pitching arm. While delivering a pitch, Dravecky sustained a spiral fracture of his humerus. Abnormal loading and muscle balance, changes in bone geometry, stress concentration, and fatigue failure may have contributed to the fracture that halted Dave Dravecky's comeback. Exploration of these biomechanical factors may help the reader contemplate a baseball pitcher's return to high performance after musculoskeletal injury, trauma, and surgery. J Orthop Sports Phys Ther 1992;16(1):2-5.

Skeletal muscle metabolism in the offspring of trained rats.

To determine the effects of maternal exercise training during pregnancy on skeletal muscle metabolism of the progeny, eleven female Sprague-Dawley rats were divided into an exercise and a control group. The maternal training group (6) ran on a rodent treadmill for 4 weeks prior to pregnancy and daily throughout gestation (21 days) at 26.8 m/min, 1 hour/day, 5 days per week. The measurements were taken 28 days postpartum. No differences were noted between the sedentary and trained maternal animals for succinic dehydrogenase (SDH), phosphofructokinase (PFK), and myosin ATPase activities of the soleus, plantaris and gastrocnemius muscles. Maternal gastrocnemius SDH and soleus PFK levels were significantly (p less than 0.05) lower than levels found in the offspring. The liver glycogen of trained maternal animals was significantly higher than that found in all other groups. As well it was shown that maternal exercise had no effect on any of the aforementioned physiological parameters measured in the pups. The results indicate that exercise training during pregnancy does not modify the skeletal muscle metabolism of the offspring as observed 28 days after birth.

Recreational exercise and occupational activity during pregnancy and birth weight: a case-control study.

OBJECTIVE: Our purpose was to investigate the impact of exercise and occupational activity on birth weight. STUDY DESIGN: This case-control study involved singleton infants at > or = 34 weeks' gestation without congenital anomalies. Case subjects had birth weights at <15th percentile for gestational age, and 2 control subjects were selected per case subject. Data were collected by self-completed questionnaire and analyzed by means of logistic regression. RESULTS: Relative to those who participated in structured exercise 3 or 4 times per week during the third trimester, the odds of lower birth weight were substantially increased for those who exercised > or = 5 times per week (adjusted odds ratio, 4.61; 95% confidence interval, 1.73-12.32) and modestly increased for those at the other extreme, who engaged in structured exercise < or = 2 times per week (adjusted odds ratio, 2.64; 95% confidence interval, 1.29-5.39). Other factors of importance to birth weight were maternal height, prepregnancy body mass, pregnancy weight gain, smoking in the third trimester, and nulliparity. CONCLUSIONS: Structured exercise frequency during late pregnancy is a determinant of birth weight.

Aerobic exercise in pregnancy: an update.

The endocrine effects of pregnancy cause striking changes in maternal metabolism, cardiovascular regulation, acid-base balance, and thermoregulation at rest and during standard submaximal exercise. The apparent purpose of these changes is to accommodate fetal needs in addition to those of the exercising woman. A significant body of evidence supports the hypothesis that healthy women can perform acute exercise of moderate intensity and duration without jeopardizing fetal well-being. Compiled studies also suggest that maximal oxygen uptake (VO2max, L.min-1) and the work rate at the onset of blood lactate accumulation (OBLA) are not significantly altered during the course of a normal pregnancy. However, some evidence suggests that maximal anaerobic power may be reduced. More information is needed on maternal cardiorespiratory function, carbohydrate metabolism, and acid-base balance at exercise intensities above OBLA and on fetal adaptability to strenuous maternal exercise. Recent studies support the view that moderate fitness conditioning can augment maternal metabolic and cardiopulmonary capacities without altering fetal development or pregnancy outcome. Implications of recent scientific studies for the design of aerobic exercise programs for pregnant women are discussed.

Effects of strenuous maternal exercise on fetal organ weights and skeletal muscle development in rats.

The purpose of the present study was to observe the effects of strenuous maternal aerobic exercise throughout gestation on fetal outcome in the rat. The strenuous exercise intensity consisted of a treadmill speed of 30 m.min-1 on a 10 degrees incline, for 120 min.day-1, 5 days.week-1. The rats were conditioned to run on a motor-driven treadmill by following a progressive two-week exercise program, so that by the end of the two weeks the rats were capable of running comfortably at this strenuous intensity in the non-pregnant state. Following the two-week running programme, the rats were paired by weight and randomly assigned to either a pregnant group that continued the running program throughout gestation (pregnant runner), or a pregnant group that did not continue the running program throughout pregnancy (pregnant control). At birth the neonates born to the pregnant running group did not differ in average neonatal body weight values, number per litter or total litter weight values when compared to controls, nor were superficial gross abnormalities observed in neonates born to the pregnant control or pregnant running groups. The strenuous maternal exercise intensity did not alter neonatal organ weight values (brain, heart, liver, lung, kidney), nor neonatal skeletal muscle (gastrocnemius, sternomastoid, diaphragm) when compared to control values. It is suggested that maternal exercise of this intensity throughout gestation does not affect fetal outcome in the rat, and may be due to the animals accustomization to the strenuous exercise protocol prior to pregnancy.

The effects of strenuous exercise on maternal rats and their developing fetuses.

Twenty young female rats were familiarized over 19 days to run comfortably on a treadmill at 30 m/min (approximately 80% VO2 max.) on a 10 degree incline for one hour. After this 19 day accustomization period the rats were separated into two groups and mated. One group (PR) continued to run on the treadmill at the prescribed rate throughout gestation and the other group (PC) was allowed to continue a normal laboratory routine. The maternal rats were weighed daily including the first day following birth and the numbers and weights of the fetuses born in each litter were noted. The results show that the fetuses were spared from any gross effects of the maternal exercise with average fetal weight and litter size being unaffected. However, there were significant differences between the maternal weights of the two groups at the end of gestation. The prepartal weight difference was 36.0g (PC group heavier) and this was reduced post-partally to 14.9g which remained significant. These differences in maternal weights were suggested to reflect a decreased amount of amniotic fluid for the fetuses of the PR group during gestation and also a reduction in maternal body fat for the PR group.

Effects of exercise on maternal glycogen storage patterns and fetal outcome in mature rats.

The purpose of the present study was to examine the effects of exercise on maternal glycogen storage patterns and fetal outcome in mature (approximately 12 months of age) Sprague-Dawley rats. The exercise consisted of treadmill running at 30 m.min-1, on a 10 degree incline, for 60 min, 5 days per week, for 4 weeks prior to pregnancy, which continued until day 19 of gestation. In mature animals, chronic exercise increased (p < 0.05) liver glycogen concentration in both pregnant and nonpregnant rats. In pregnant exercised animals, the glycogen concentration of the maternal liver increased almost twofold (p < 0.05) compared with the sedentary pregnant group. There was no difference in the amount of glycogen stored in the gastrocnemius or soleus muscles in response to training, pregnancy, or chronic maternal exercise in the mature rat. In the pregnant groups, there were fewer (p < 0.05) viable fetuses and more (p < 0.05) resorption sites than in young rats. In addition, exercise during pregnancy in the mature animal decreased (p < 0.05) fetal body weight. These results demonstrate that a conflict may exist between maternal exercise and fetal demands for energy in the mature rat. This conflict seems to favour the maternal system, as evidenced by the enhanced maternal liver glycogen storage and the negative effect on fetal growth.

The effects of strenuous maternal exercise during gestation on maternal body components in rats.

The effects of strenuous maternal exercise throughout gestation on the maternal rat were examined. The results indicated that maternal exercise of this nature (30 metres/minute, 10 degree incline, 120 minutes/day, 5 days/week) caused a significant decrease in the amount of weight gained by the running maternal rats when compared to controls. By analysing the maternal rat and various bodily components after parturition, it was suggested that subcutaneous tissue growth (fat deposits and mammary gland tissue) was significantly less in the running group. The carcass remainder component was also found to weigh less in the running group, even though the maternal running rats had just given birth to an equivalent (not significantly different) number of neonates of similar (not significantly different) weight to the control group.

Effect of water temperature on exercise-induced maternal hyperthermia on fetal development in rats.

The objective of this study was to determine if water temperature influenced exercise-induced hyperthermia in swim-trained pregnant rats and the resulting fetal development. Pregnant Sprague-Dawley rats with 6 weeks pre-pregnancy training were exercised daily from day 1 to day 18 of gestation in water that was 34.6 +/- 0.4 degrees C (Cool Water Swimmers--CWS) or 37.6 +/- 0.1 degrees C (Warm Water Swimmers--WWS), for one hour/day. During this time period another group of pregnant rats was immersed to the neck in warm water (37.6 +/- 0.2 degrees C) (Warm Water Controls--WWC). On day 19 of gestation all animals were sacrificed and fetal development assessed. Maternal exercise in warm water elevated maternal body core temperature by 2.3 +/- 0.1 degrees C above resting values, with an increase in fetal abnormalities compared to the same exercise intensity in cool water. Fifty-eight percent of the abnormal fetuses and 60% of the resorption sites were found in the WWS group. Of the abnormalities determined, 65% were from the WWS group and 45% of these fetuses showed micrencephaly. Results suggest cool water may regulate maternal body temperature during swimming exercise and that swimming in warm water should be avoided during gestation because of potential teratogenic effects.

Effect of maternal exercise on fetal and placental glycogen storage in the mature rat.

The purpose was to determine the effects of exercise on fetal and placental glycogen storage patterns at 20 days gestation (term 21 days) in mature (approximately 12 months of age) Sprague-Dawley rats. The exercise protocol consisted of treadmill running at 30 m min-1, on a 10 incline, for 60 min, 5 days per week, for 4 weeks prior to conception, which continued until day 19 of pregnancy. Exercise produced a significant reduction in fetal body weight, placental weight, and fetal organ weights (heart, kidney, brain, and liver) compared to sedentary control animals (p <.05). However, when fetal body size was taken into account, these differences disappeared, except for the fetal brain:body weight ratio, which was larger in the exercised animals compared to controls (p <.05). Fetal liver glycogen concentrations were significantly lower in exercised animals compared to nonrunning control animals (p <.05). These results demonstrate that exercise of mature rats may compromise fetal development and hepatic glycogen storage in the fetus.

Glycogen storage in fetuses of trained pregnant rats.

The purpose was to determine if running 30 m/min on a 10 degrees incline, 60 min/day for 5 days/ week altered fetal glycogen storage in prepregnancy trained rats. Animals that exercised for 3 weeks prior to pregnancy either continued the same exercise program until Day 19 of gestation (pregnant running group [PR]), or ceased exercising at conception (pregnant controls [PC]). A separate set of animals did not exercise either before or during pregnancy (pregnant nonrunning control group [PNRC]). On Day 20 of gestation, fetal organs and placenta were weighted and analyzed for glycogen concentration. Glycogen concentrations were not different in either fetal liver, heart, or placenta of PR rats compared to PNRC animals. However, fetal liver glycogen concentration was significantly lower in the fetal heart and liver of PC animals compared to glycogen measured in both PNRC and PR animals (p < .05). These results suggest that exercise of this intensity does not compromise fetal glycogen storage in trained pregnant rats. However, chronic prepregnancy exercise and then abrupt cessation of exercise at conception may compromise fetal growth and development.