Human maternal and fetal response to graded exercise

Six healthy active women in the third trimester of pregnancy participated in a graded exercise protocol to levels of exertion perceived to be equivalent to that of their usual exercise regimen. Fetal heart rate response (FHR) was documented by ultrasound transducer and confirmed (n = 1) by ultrasonic visualization. Resting maternal O2 consumption was 277 +/- 50 (SD) ml/min and rose to 1,132 +/- 202 ml/min at a mean final exercise intensity of 79 +/- 9 W after 12.8 +/- 1.7 min on a cycle ergometer. There was no significant change in maternal serum insulin, growth hormone, glucose, or pH values. Maternal leukocyte count, hemoglobin, and venous lactate levels rose significantly during the exercise (P less than 0.05). FHR prior to exercise was 142 +/- 4 beats/min and decreased to 84 +/- 34 beats/min during exercise. The decrease in FHR was documented within 1 min of initiating exercise in all cases. During exercise, fetal movements were not accompanied by FHR accelerations. Within 1 min following the cessation of exercise, FHR rose to 143 +/- 8 beats/min and fetal movements were accompanied by FHR accelerations. Since the recovery of FHR occurred immediately after cessation of maternal exercise, this level of maternal exercise does not appear to be harmful to the fetus.     

Influence of exercise training on maternal and fetal morphological characteristics in the rat

Evidence in both humans and animals has shown that exercise before or during pregnancy may effect fetal outcome. The purpose of this investigation was to examine the effects of an exercise program on fetal development in the rat. Prior to impregnation one group of animals was exercise-trained on a Quinton shock-stimulus rodent treadmill. The exercised group was trained to run 5 days/wk, for 2.0 h/day at 31 m/min up an 8 degree incline for 8 wk before mating. Following mating the training intensity was reduced to 27 m/min up a 5 degree incline, and the exercise period decreased to 1 h/day. On day 19 of gestation, 24 h postexercise for the trained mothers, the animals were killed in the fed state and the maternal and fetal characteristics were measured. The sedentary controls gained significantly (P less than 0.05) more body weight during pregnancy. This can be attributed to three factors: higher number of fetuses, 14.83 +/- 0.04 vs. 12.2 +/- 0.85 for the trained; larger litter weights, 44.25 +/- 4.97 vs. 26.17 +/- 1.82 g/dam for the trained; and slightly larger lipid stores. In addition to having fewer pups the trained mothers had a greater number of fetal resorptions; 0.9/dam as opposed to 0.17/dam for the sedentary control. Analysis of fetal body composition showed no difference in total body water, protein, or fat between the pups of sedentary and trained dams. The results of this study indicate that exercise training prior to and during pregnancy influences fetal development in the rat.     

Changes of maternal and fetal pituitary-adrenocortical functions during human labour

The results of maternal 11-hydroxycorticoid (11-OHCS) determination on blood obtained from four stages of 44 spontaneous labour cases showed a strong and time-related maternal adrenocortical activation during vaginal delivery. The high 11-OHCS level in the cord blood and the increase of the 11-OHCS concentration in the amniotic fluid suggested the same response of the fetal adrenal. However, in 14 cases of elective caesarean sections the 11-OHCS levels in the cord blood and the amniotic fluid did not rise in spite of the elevated maternal plasma 11-OHCS content.     

Nitrogen flux across ovine maternal and fetal hindquarters during fasting

Nitrogen flux across the hindquarters of fetal and maternal sheep (n = 15) was determined during normal feeding and following 5 days of maternal fasting. Arterial and venous whole blood concentrations of free amino acids, ammonia and oxygen were measured entering and exiting the hindquarters. Further, the DNA, protein and nitrogen contents of the hindlimb skeletal muscle of the fetus were determined in the fed state and following the 5-day fast. Results of these studies indicate that maternal and fetal hindlimb metabolism differ during fasting. There is a net efflux of alanine, glutamine and total nitrogen from the maternal hindquarters following 5 days of fasting. The fetus also releases glutamine and alanine from the hindquarters during the fast, presumably as potential energy substrate. However, nitrogen balance across the fetal hindquarter remains positive as a result of increased positive arteriovenous differences for other amino acids (particularly leucine and isoleucine). The concentrations of DNA, protein and nitrogen in fetal skeletal muscle remain unchanged during fasting. These data indicate that, whereas the mother undergoes protein catabolism and net nitrogen loss from the hindquarter during fasting, the fetus maintains a positive nitrogen balance across the hindquarter.     

Effect of maternal weight gain during pregnancy on exercise performance

We examined the effect of maternal weight gain during pregnancy on exercise performance. Ten women performed submaximal cycle (up to 60 W) and treadmill (4 km/h, up to 10% grade) exercise tests at 34 +/- 1.5 (SD) wk gestation and 7.6 +/- 1.7 wk postpartum. Postpartum subjects wearing weighted belts designed to equal their body weight during the antepartum tests performed two additional treadmill tests. Absolute O2 uptake (VO2) at the same work load was higher during pregnancy than postpartum during cycle (1.04 +/- 0.08 vs. 0.95 +/- 0.09 l/min, P = 0.014), treadmill (1.45 +/- 0.19 vs. 1.27 +/- 0.20 l/min, P = 0.0002), and weighted treadmill (1.45 +/ 0.19 vs. 1.36 +/- 0.20 l/min, P = 0.04) exercise. None of these differences remained, however, when VO2 was expressed per kilogram of body weight. Maximal VO2 (VO2max) estimated from the individual heart rate-VO2 curves was the same during and after pregnancy during cycling (1.96 +/- 0.37 to 1.98 +/- 0.39 l/min), whereas estimated VO2max increased postpartum during treadmill (2.04 +/- 0.38 to 2.21 +/- 0.36 l/min, P = 0.03) and weighted treadmill (2.04 +/- 0.38 to 2.19 +/- 0.38 l/min, P = 0.03) exercise. We conclude that increased body weight during pregnancy compared with the postpartum period accounts for 75% of the increased VO2 during submaximal weight-bearing exertion in pregnancy and contributes to reduced exercise capacity. The postpartum increase in estimated VO2max during weight-bearing exercise is the result of consistently higher antepartum heart rates during all submaximal work loads.     

Effect of maternal exercise on fetal liver glycogen late in gestation in the rat

To determine the effect of maternal exercise on fetal liver glycogen content, fed and fasted rats that were pregnant for 20.5 or 21.5 days were run on a rodent treadmill for 60 min at 12 m/min with a 0% grade or 16 m/min up a 10% grade. The rats were anesthetized by intravenous injection of pentobarbital sodium, and fetal and maternal liver and plasma samples were collected and frozen. Fetal liver glycogenolysis did not occur as a result of maternal exercise. Fetal blood levels of lactate increased 22-60%, but glucose, plasma glucagon, and insulin were unchanged during maternal exercise. Maternal liver glycogen decreased as a result of exercise in all groups of rats except the fasted 20.5-day-pregnant group. Plasma free fatty acids increased in all groups and blood lactate increased in fed (20.5 days) and fasted (21.5 days) pregnant rats. Maternal glucose, glucagon, and insulin values remained constant during exercise. The fetus appears to be well-protected from metabolic stress during moderate-intensity maternal exercise.     

Thermal bradycardia during radiofrequency irradiation

The present study was performed to determine if any heart rate or blood pressure changes occur during intermittent exposure to radiofrequency radiation (RFR), and to determine if parasympathetic blockade due to atropine has any effect on these changes or on thermal responses. Anesthetized rats were exposed to 2.8 GHz pulsed RFR at an average power level of 60 mW/cm2 (average specific absorption rate, 14 W/kg). During an initial exposure period to raise colonic temperature to 39.5 degrees C, heart rate decreased significantly. This thermal bradycardia is similar to that reported by other investigators during environmental heat exposure. Intermittent exposure to radiation, which was designed to result in 1 degree C colonic temperature changes, did not significantly affect heart rate or mean arterial blood pressure, before or after atropine administration. The time courses of these 1 degree C temperature changes were not altered significantly by atropine. Following administration of atropine, the thermal bradycardia during the initial heating period was still evident. Thus, factors other than vagal activity are responsible for the phenomenon. It is possible that the bradycardia is a consequence of a general reduction in metabolism, which occurs also during environmental heat exposure.     

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.     

Effect of exercise during pregnancy, graded as a percentage of aerobic capacity: maternal and fetal responses of the rat.

1. A number of variables were studied in pregnant rats that underwent strenuous exercise during pregnancy. They were: total weight gain, daily weight gain, length of pregnancy, number of offspring. Also the weight, the heart weight and fibre/capillary ratio of the newborn male rats and their VO2 max at 90 days were measured. 2. The exercise was graded in accordance to previous aerobic capacity as determined by VO2 max with relative loads of 60% (E60), 70% (E70), 80% (E80) and 90% (E90) of VO2 max being applied to the various groups (N = 6 per group). 3. The total weight gain and daily weight gain was significantly less in the E70, E80 and E90 groups. Weight gain in the anabolic phase (0-14d) was not different, but during the first week the weight gain in the E90 group was significantly less than control group. In the catabolic phase the observations were similar the first week of the anabolic phase. 4. Length of pregnancy, heart weight offspring and VO2 max of 90-day-old male rats were not significantly different. The number of offspring of the E90 group was significantly smaller than the control, E60 and E70 groups. 5. The offspring body weight was less in the E70, E80 and E90 groups than control group and was significantly less in the E90 group compared to the E60 and E70 groups. 6. The fibre/capillary ratio of the offspring was different in the E90 group compared to the control group. 7. These results suggest that the effect of exercise depends on the relative work load applied to the mother and these effects are particularly marked at high work loads.     

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 effect of clothing on "diving bradycardia" in man during submersion in cold water

Eighteen healthy male volunteers undertook three seated submersions into stirred water at 5 degrees C. Whilst submerged, the subjects attempted to hold their breath for 20 s. They wore a different clothing assembly for each submersion, viz: a cotton overall assembly, a "wet suit" assembly and a "dry suit" assembly. During the experiments the breath-hold time, heart rate, skin and rectal temperatures of the subjects were recorded. The results showed that significantly (P less than 0.05) more subjects developed a diving bradycardia--defined as five or more consecutive R-R intervals of over 1.2 s--when wearing the dry suit. It is concluded that increasing the cold stress experienced by individuals during cold-water submersion decreases the incidence of diving bradycardia but not the magnitude of the bradycardia when it occurs.     

Haematological values during normal reproduction of the maternal and the fetal rabbit

1. Haematological values of non-pregnant/non-lactating, pregnant as well as lactating rabbits and 28-day-old fetuses were measured. 2. The haemoglobin content in does decreased during the observed periods from 122 +/- 8 g/l to 100 +/- 11 g/l. In 28-day-old fetuses it was 85 +/- 0 g/l. 3. The erythrocyte count in 28-day-old fetuses was 2.4 X 10(12)/l. In the does, the erythrocyte count was 5.2 X 10(12)/l in week 4 of gestation. The erythrocyte volume in fetuses was about 45% higher than that of the doe. 4. In fetuses the leucocyte count was approximately one ninth that of the mother in week 4 of gestation (0.41 +/- 0.08 X 10(9)/l vs 3.8 +/- 0.4 X 10(9)/l).     

Doppler evaluation of maternal and fetal vessels during normal gestation in rabbits

The aim of this work was to evaluate the hemodynamic changes in the utero-placental arterial vessels in rabbits (Orictolagus cuniculus) throughout pregnancy as well as those in the umbilical cord, aorta, and caudal vena cava of fetuses to establish their normal reference ranges for systolic peak velocity (SPV), end diastolic velocity (EDV), pulsatility index (PI), and resistance index (RI). The blood flow waveforms were monitored every 4 d in 10 rabbits from Day 10 of pregnancy onward by means of color and pulsed wave Doppler ultrasonography using a 5.5-7.5 MHz microconvex transabdominal probe. The utero-placental blood flow was characterized by steep increases and decrease in the SPV with a slow diastolic wave and relatively high EDV, whereas that of the umbilical artery was discontinuous until Day 22 of pregnancy, when a diastolic waveform was also detectable. From Day 10 to 22 of pregnancy, the fetal aorta blood flow was discontinuous, but thereafter a diastolic peak was measurable. The blood flow of the fetal caudal vena cava was characterized by a systolic peak followed by a small diastolic peak. Throughout the gestation, the SPV and the EDV of maternal and fetal vessels increased (α < 0.05), whereas the PI and the RI decreased (α < 0.05), except for the utero-placental vessels. This work confirms that the rabbit could also be a valid experimental animal model to study, by Doppler ultrasonography, functional hemodynamic changes of the fetuses and placenta vessels in both normal and pathophysiologic conditions.     

Voluntary exercise in pregnant rats positively influences fetal growth without initiating a maternal physiological stress response

The effects of increased physical activity during pregnancy on the health of the offspring in later life are unknown. Research in this field requires an animal model of exercise during pregnancy that is sufficiently strenuous to cause an effect but does not elicit a stress response. Previously, we demonstrated that two models of voluntary exercise in the nonpregnant rat, tower climbing and rising to an erect bipedal stance (squat), cause bone modeling without elevating the stress hormone corticosterone. In this study, these same models were applied to pregnant rats. Gravid Wistar rats were randomly divided into three groups: control, tower climbing, and squat exercise. The rats exercised throughout pregnancy and were killed at day 19. Maternal stress was assessed by fecal corticosterone measurement. Maternal bone and soft tissue responses to exercise were assessed by peripheral quantitative computed tomography and dual-energy X-ray absorptiometry. Maternal weight gain during the first 19 days of pregnancy was less in exercised than in nonexercised pregnant control rats. Fecal corticosterone levels did not differ between the three maternal groups. The fetuses responded to maternal exercise in a uterine position-dependent manner. Mid-uterine horn fetuses from the squat exercise group were heavier (P < 0.0001) and longer (P < 0.0001) and had a greater placental weight (P = 0.001) than those from control rats. Fetuses from tower-climbing dams were longer (P < 0.0001) and had heavier placentas (P = 0.01) than those from control rats, but fetal weight did not differ from controls. These models of voluntary exercise in the rat may be useful for future studies of the effects of exercise during pregnancy on the developmental origins of health and disease.     

The bone-muscle ratio of fetal lambs is affected more by maternal nutrition during pregnancy than by maternal size

Bone formation and loss are related to the strain imposed on bone by muscle forces. Bone mineral content (BMC) and lean mass (LM) of fetal lambs was determined at day 140 of pregnancy in 8 groups of ewes, which were of either large or small body size, on either high (ad libitum) or maintenance pasture intake from day 21 of pregnancy, or carrying either singletons or twins. BMC and LM (using DXA scanning) of fetal hindquarters/spine were corrected to leg length. BMC and LM were less in twin than singleton groups (P < 0.001). Large ewes on high intake produced single fetuses with a (group mean) BMC/LM ratio that was higher (P < 0.002) than that in fetuses of large ewes with singletons on maintenance intake or twins on either high or maintenance intakes, the ratios of which were not different. In single fetuses from small ewes on high intake, the BMC/LM ratio was higher than those from small ewes with singletons on maintenance intake or twins on either high or maintenance intakes, the ratios of which were not different. The ratio was not different in singleton fetuses of ewes on high intake, whether they were large or small. Different fetal environments resulted in a given amount of muscle being associated with a higher or lower bone mass. Dietary intake during pregnancy was more important than maternal size in affecting the ratio. We conclude that intrauterine environmental factors may be important in determining bone mass postnatally, and possibly later in life.     

Steadiness of oxygen tension in the fetal brain during changes in maternal oxygenation

In acute experiments on pregnant rats (86) and their fetuses (76) the authors studied oxygen tension in the brain of the developing organism. In inhalation PO2 in the brain of the fetus practically did not change.     

"Psyching-up" enhances force production during the bench press exercise

We investigated the effect of "psyching-up" on force production during the bench press. Twelve men (mean age +/- SD: 27.4 +/- 11.2 years) and 8 women (20.9 +/- 2.5 years) with strength-training experience performed 5 bench press repetitions on a modified Biodex isokinetic dynamometer during 3 interventions. The interventions were counterbalanced and included a free-choice psych-up, a cognitive distraction, and an attention-placebo. Peak force recorded after psyching-up (mean +/- SD: 764 +/- 269 N.m) was significantly different from both distraction (703 +/- 282 N.m, p = 0.003) and attention-placebo (708 +/- 248 N.m, p = 0.01). The mean percentage increase in peak force from distraction to psyching-up was 11.8% (6 to 18%, 95% confidence interval [CI]) and 8.1% from placebo to psyching-up (3 to 13%, 95% CI). The results of the present study indicate that psyching-up may increase force production during the bench press exercise in participants with at least 1 year strength-training experience.