Aerobic exercise during pregnancy. Special considerations

A narrative review of exercise dose during pregnancy

The current recommendations for prenatal exercise dose align with those from the American College of Sports Medicine; 150 min of moderate intensity every week of pregnancy. However, recent works suggest there may be a dose-dependent beneficial effect for mother and offspring; maternal and offspring health outcomes respond differently to low, medium, and high doses of prenatal exercise. It is, therefore, our aim to summarize the published evidence (years 1950-2023) for five metrics of prenatal exercise training commonly reported, that is, "FITT-V": Frequency (number of sessions), Intensity (metabolic equivalents "METs"), Time (duration of sessions), Type (exercise mode), Volume (exercise MET*mins). The target audience includes clinicians and health care professionals, as well as exercise professionals and physiologists. Data suggest that moderate exercise frequency (3-4 times weekly) appears safe and efficacious for mother and offspring, while there is contradictory evidence for the safety and further benefit of increased frequency beyond 5 sessions per week. Moderate (3-6 METs) and vigorous (>6 METs) intensity prenatal exercise have been shown to promote maternal and offspring health, while little research has been performed on low-intensity (<3 METs) exercise. Exercise sessions lasting less than 1 hr are safe for mother and fetus, while longer-duration exercise should be carefully considered and monitored. Taken together, aerobic, resistance, or a combination of exercise types is well tolerated at medium-to-high volumes and offers a variety of type-specific benefits. Still, research is needed to define (1) the "minimum" effective dose of exercise for mother and offspring health, as well as (2) the maximum tolerable dose from which more benefits may be seen. Additionally, there is a lack of randomized controlled trials addressing exercise doses during the three trimesters of pregnancy. Further, the protocols adopted in research studies should be more standardized and tested for efficacy in different populations of gravid women.

Maximizing Recovery in the Postpartum Period: A Timeline for Rehabilitation from Pregnancy through Return to Sport

Increased participation and duration in sport has become commonplace for women with their involvement often including the transition to motherhood in the peak of their athletic careers. No rehabilitation models that assess the full spectrum of pregnancy to postpartum have been developed for women to assist in safe exercise progressions that reduce postpartum symptoms and optimize performance during the return to full activity. Referral to physical therapy both in the prenatal and postnatal period is currently not considered standard of care to reduce prevalence of symptoms such as musculoskeletal pain, diastasis recti, and pelvic floor dysfunction which may ultimately interfere with physical activity and performance. This commentary presents a timeline and suggested progression for exercise participation to improve awareness of the musculoskeletal changes that occur after labor and delivery. The concepts covered may increase the understanding of how to manage pregnant and postpartum athletes from a musculoskeletal perspective and serve as a starting point for establishing appropriate and guided rehabilitation for safe return to sport after childbirth.

Resistance Training Does Not Decrease Placental Blood Flow During Valsalva Maneuver: A Novel Use of 3D Doppler Power Flow Ultrasonography

BACKGROUND

The Valsalva maneuver may increase maternal blood pressure and intra-abdominal pressure, resulting in decreased blood flow to the fetus during resistance training.

HYPOTHESIS

There is no significant reduction in placental blood flow in pregnancy during resistance training in recreational athletes, as documented by a 3-dimensional power flow Doppler ultrasonography.

STUDY DESIGN

Cohort.

LEVEL OF EVIDENCE

Level 3.

METHODS

A cohort of healthy women who participated in recreational athletics was enrolled in a prospective study to assess placental blood flow during a resistance exercise. A 1 repetition maximum (1RM, up to 50 lb) was determined through a modified chest press as a marker of heavy resistance training. Three-dimensional volume measurements and power Doppler flow were determined at the rest phase and during the 1RM lift phase. The vascular flow index (VFI) was calculated to determine placental perfusion during each phase.

RESULTS

A total of 22 women participated. The mean age of participants was 31 years. Gestational age ranged from 13 to 28 weeks. Average 1RM weight lifted was 30 lb. Four women (18%) were able to lift 50 lb, the maximum weight that the study allowed. The remaining 18 women (82%) lifted their true 1RM. Mean VFI during lift phase was 2.185 compared with 2.071 at rest (P = 0.03). There was a slight mean increase in VFI during lift phase, 0.114 (95% CI 0.009-0.182) from 2.071 to 2.185 with lifting (P = 0.03). The 15 women who participated in structured exercise had a mean VFI at rest and during the lift phase of 2.031 and 2.203, respectively (P = 0.01).

CONCLUSION

Three-dimensional power flow Doppler imaging can guide resistance training during pregnancy to prevent fetal injury due to hypoperfusion. Resistance training up to an RM1 of 50 lb did not result in a significant reduction of placental blood flow from resting state in the study population.

CLINICAL RELEVANCE

This technique may be used to guide training parameters among pregnant athletes.

Cardiac Physiology of Pregnancy

Although the physiology of the heart and vascular system has not changed, there are many things we have learned and are still learning today. Research related to heart adaptations during pregnancy has been performed since the 1930s. Since the mid-1950s, researchers began to look at changes in the maternal cardiovascular system during exercise while pregnant. Research related to exercise during pregnancy and offspring heart development began and has continued since the 1970s. We will review the normal female cardiovascular system adaptations to pregnancy in general. Additionally, topics related to maternal cardiac adaptations to pregnancy during acute exercise, as well as the chronic conditioning response from exercise training will be explored. Since physical activity during pregnancy influences fetal development, the fetal cardiac development will be discussed in regards to acute and chronic maternal exercise. Similarly, the influence of various types of maternal exercise on acute and chronic fetal heart responses will be described. Briefly, the topics related to how and if there is maternal-fetal synchrony will be explained. Lastly, the developmental changes of the fetal cardiovascular system that persist after birth will be explored. Overall, the article will discuss maternal cardiac physiology related to changes with normal pregnancy, and exercise during pregnancy, as well as fetal cardiac physiology related to changes with normal development, and exercise during pregnancy as well as developmental changes in offspring after birth.

Water aerobics II: maternal body composition and perinatal outcomes after a program for low risk pregnant women

BACKGROUND

To evaluate the effectiveness and safety of water aerobics during pregnancy.

METHODS

A randomized controlled trial carried out in 71 low-risk sedentary pregnant women, randomly allocated to water aerobics or no physical exercise. Maternal body composition and perinatal outcomes were evaluated. For statistical analysis Chi-square, Fisher's or Student's t-tests were applied. Risk ratios and their 95% CI were estimated for main outcomes. Body composition was evaluated across time using MANOVA or Friedman multiple analysis.

RESULTS

There were no significant differences between the groups regarding maternal weight gain, BMI or percentage of body fat during pregnancy. Incidence of preterm births (RR = 0.84; 95%CI:0.28-2.53), vaginal births (RR = 1.24; 95%CI:0.73-2.09), low birthweight (RR = 1.30; 95%CI:0.61-2.79) and adequate weight for gestational age (RR = 1.50; 95%CI:0.65-3.48) were also not significantly different between groups. There were no significant differences in systolic and diastolic blood pressure and heart rate between before and immediately after the water aerobics session.

CONCLUSION

Water aerobics for sedentary pregnant women proved to be safe and was not associated with any alteration in maternal body composition, type of delivery, preterm birth rate, neonatal well-being or weight.

Need for Population Specific Validation of a Portable Metabolic Testing System: A Case of Sedentary Pregnant Women

Commercially available portable metabolic systems have been validated with samples of young, healthy, and well-fit subjects, but use of these systems with a special population, such as healthy but sedentary pregnant women, requires a unique set of considerations. These include a woman’s limited testing time necessary for fetal safety, relatively low oxygen consumption, and the unique physiology of pregnancy (woman, the placenta, and the fetus). The purpose of this study was to validate a portable metabolic testing system (VO2000) with healthy sedentary pregnant women. A total of 9 sedentary pregnant women who averaged 30 years of age (SD = 3), 93 kg (SD = 19) weight, 163 cm (SD = 7) height, and at 19 weeks’ gestation (SD = 5) volunteered to participate. Submaximum fitness tests using the Cornell protocol were conducted once with two systems (VO2000 and CPX/D, a reference) simultaneously, and then subsequently twice with one system (VO2000). The VO2000 consistently overestimated VO2 measurement, compared to the same manufacturer’s reference system, by 4.4 +/− 3.6 (SD) ml/kg/min, and when VO2000 was used twice, the mean difference was statistically significant (1.0 +/− 1.8 [SD] ml/kg/min; t(45) = 3.9, p < .001). The results of the study show that although VO2000 is an established and validated portable metabolic system for measurement on adult males and females who are relatively well fit, this portable system consistently overestimates VO2 readings for pregnant women compared to standard full-size system. Measurements, when repeated, were not consistent.

Substrate utilization and hormonal responses to moderate intensity exercise during pregnancy and after delivery

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.

Maternal rectal temperature and fetal heart rate responses to upright cycling in late pregnancy

OBJECTIVE

To assess maternal rectal temperature and fetal heart rate responses to dynamic exercise.

METHODS

11 healthy women with low risk pregnancies completed three separate upright cycling tests at 34 to 37 weeks gestation: 15 min at 62.5 W (mean maternal heart rate [MHR] 138 beats.min-1 (test A); 15 min at 87.5 W (MHR 156 beats.min-1) (test B); and 30 min at 62.5 W (MHR 142 beats.min-1) (test C). Rectal temperature and fetal heart rate were measured.

RESULTS

Mean temperature increase after tests B and C [by 0.4(SD 0.1) degrees C] was greater than after test A [0.2(0.1) degrees C] (P < 0.001). Fetal heart rate, measured in the recovery period immediately after exercise, increased significantly only after tests B and C (P < 0.01). Exercise related changes in temperature and fetal heart rate weakly correlated in tests B (P < 0.02) and C (P < 0.01).

CONCLUSIONS

Temperature and fetal heart rate changes were more marked after higher intensity (test B) or longer duration exercise (test C) compared with moderate exercise, but none of the tests caused adverse fetal heart rate changes (decrease in accelerations, bradycardia, or decelerations) or individual temperatures above 38 degrees C.

Position of the American Dietetic Association and the Canadian Dietetic Association: nutrition for physical fitness and athletic performance for adults

The importance of diet and healthful food choices in optimizing health status, fitness levels, and athletic performance has been recognized by both participants and professionals. There continues to be a need for the interpretation of new research findings in this fast-growing discipline and for the dissemination of nutrition information and training techniques for a broad spectrum of individuals involved in various forms of physical activity. The registered dietitian who has specialized in exercise physiology and sports nutrition has the knowledge and counseling skills to act as the provider of this nutrition information. Additional information may be obtained in the Sports Nutrition Manual, 2nd edition, published by The American Dietetic Association and the Sports and Cardiovascular Nutrition dietetic practice group as well as in Sport Nutrition for the Athletes of Canada, published by the Sport Nutrition Advisory Committee of the Sports Medicine and Science Council of Canada.

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.

Fetal heart rate response to sustained recreational exercise

OBJECTIVE

We aimed to test the hypotheses that fetal heart rate increases during and after sustained exercise and that the magnitude of the increases is related to gestational age and the duration, intensity, and type of exercise.

STUDY DESIGN

Maternal oxygen uptake and fetal heart rate were monitored in 120 regularly exercising women in association with routine 20-minute workouts between 16 and 39 weeks' gestation.

RESULTS

In 97% of the studies fetal heart rate increased during and after exercise. This was significant at all gestational ages and with all forms of exercise with an overall increase of 15 +/- 11 beats.min-1 at 60% +/- 12% of maximal aerobic capacity (mean +/- SD). The magnitude increased with gestational age (10 +/- 8 to 20 +/- 11 beats.min-1), exercise intensity (8 +/- 7 to 21 +/- 13 beats.min-1), and exercise duration (8 +/- 4 to 16 +/- 7 beats.min-1).

CONCLUSION

We concluded that the hypothesis is correct and speculate that these changes represent a maturing fetal response to a reduction in Po2.

Effect of recreational exercise on midtrimester placental growth

OBJECTIVE

The purpose of our study was to test the hypothesis that regular recreational exercise increases the rate of growth in placental volume in the midtrimester of human pregnancy.

STUDY DESIGN

Serial measurements of placental volume were obtained between the fourteenth and twenty-sixth gestational week in 18 subjects who exercised regularly throughout the midtrimester and in 16 matched controls with an ultrasonographic system equipped with a fixed-base, articulated-arm, 3.5 MHz B-mode transducer.

RESULTS

Placental volumes were significantly greater in the women who maintained a regular exercise regimen throughout the midtrimester. At 16 weeks (mean +/- SD) volumes were 141 +/- 34 cm3 and 106 +/- 18 cm3 in the two groups. This difference increased at 20 weeks (265 +/- 67 cm3 vs 186 +/- 46 cm3) and again at 24 (410 +/- 87 cm3 vs 270 +/- 58 cm3) weeks' gestation because of a significant between-group difference in the rate of growth in placental volume over this time interval (34 +/- 8 cm3/wk vs 21 +/- cm3/wk).

CONCLUSION

We conclude that the hypothesis is correct and speculate that the change in growth rate represents an adaptive response to the intermittent stimulus of a reduction in regional blood flow.