Substrate and hormonal responses during exercise classes at selected stages of pregnancy

Sex Differences in Energy Metabolism: A Female-Oriented Discussion

The purpose of this review is to delineate aspects of energy metabolism at rest and during exercise that may be subject to sex differences and the potential underlying mechanisms involved. It focuses on distinct aspects of female physiology with an oriented discussion following the reproductive life stages of healthy, eumenorrheic females, including premenopausal time frames, pregnancy, perimenopause, and menopause. Finally, this review aims to address methodological challenges surrounding sexual dimorphism in energy metabolism investigations and confounding factors in this field. During resting conditions, females tend to have higher rates of non-oxidative free fatty acid clearance, which could contribute to lower respiratory exchange ratio measures. At the same time, carbohydrate energy metabolism findings are mixed. In general, females favor lipid energy metabolism during moderate-intensity exercise, while men favor carbohydrate energy metabolism. Factors such as age, dietary intake, genetics, and methodological decisions confound study findings, including properly identifying and reporting the menstrual cycle phase when female subjects are eumenorrheic. Pregnancy presents a unique shift in physiological systems, including energy metabolism, which can be observed at rest and during exercise. Changes in body composition and hormonal levels during the post-menopausal period directly impact energy metabolism, specifically lipid metabolism. This change in physiological state factors into the evidence showing a reduction in our understanding of sex differences in lipid metabolism during exercise in older adults. This review reveals a need for a focused understanding of female energy metabolism that could help exercise and nutrition professionals optimize female health and performance across the lifespan.

The Effect of Maternal Diet and Physical Activity on the Epigenome of the Offspring

The aim of this review was to examine the current literature regarding the effect of maternal lifestyle interventions (i.e., diet and physical activity) on the epigenome of the offspring. PubMed, Scopus and Cochrane-CENTRAL were screened until 8 July 2023. Only randomized controlled trials (RCTs) where a lifestyle intervention was compared to no intervention (standard care) were included. Outcome variables included DNA methylation, miRNA expression, and histone modifications. A qualitative approach was used for the consideration of the studies' results. Seven studies and 1765 mother-child pairs were assessed. The most common types of intervention were dietary advice, physical activity, and following a specific diet (olive oil). The included studies correlated the lifestyle and physical activity intervention in pregnancy to genome-wide or gene-specific differential methylation and miRNA expression in the cord blood or the placenta. An intervention of diet and physical activity in pregnancy was found to be associated with slight changes in the epigenome (DNA methylation and miRNA expression) in fetal tissues. The regions involved were related to adiposity, metabolic processes, type 2 diabetes, birth weight, or growth. However, not all studies showed significant differences in DNA methylation. Further studies with similar parameters are needed to have robust and comparable results and determine the biological role of such modifications.

Influence of Menstrual Cycle or Hormonal Contraceptive Phase on Physiological Variables Monitored During Treadmill Testing

Purpose: To examine the influence of menstrual cycle (MC) and hormonal contraceptive (HC) cycle phases on physiological variables monitored during incremental treadmill testing in physically active women (eumenorrheic, EUM = 16 and monophasic HC-users, CHC = 12).

Methods: Four running tests to exhaustion were performed at bleeding, mid follicular (mid FOL)/active 1, ovulation/active 2, and mid luteal (mid LUT)/inactive. HC and MC phases were confirmed from serum hormones. Heart rate (HR), blood lactate (Bla), and V˙O₂ were monitored, while aerobic (AerT) and anaerobic (AnaT) thresholds were determined. V˙O_2peak, maximal running speed (RUN_peak), and total running time (RUN_total) were recorded.

Results: No significant changes were observed in V˙O₂ or Bla at AerT or AnaT across phases in either group. At maximal effort, absolute and relative V˙O_2peak, RUN_peak, and RUN_total remained stable across phases in both groups. No significant fluctuations in HR_max were observed across phases, but HR at both AerT and AnaT tended to be lower in EUM than in CHC across phases.

Conclusion: Hormonal fluctuations over the MC and HC do not systematically influence physiological variables monitored during incremental treadmill testing. Between group differences in HR at AerT and AnaT underline why HR-based training should be prescribed individually, while recording of MC or HC use when testing should be encouraged as phase may explain minor, but possibly meaningful, changes in, e.g., Bla concentrations or differences in HR response.

Does exercise during pregnancy impact organs or structures of the maternal-fetal interface?

Exercise during pregnancy has been shown to be associated with improved health outcomes both during and after pregnancy for mother and fetus across the lifespan. Increasing physical activity and reducing sedentary behaviour during pregnancy have been recommended by many researchers and clinicians-alike. It is thought that the placenta plays a central role in mediating any positive or negative pregnancy outcomes. The positive outcomes obtained through prenatal exercise are postulated to result from exercise-induced regulation of maternal physiology and placental development. Considerable research has been performed to understand the placenta's role in pregnancy-related diseases, such as preeclampsia, fetal growth restriction, and gestational diabetes mellitus. However, little research has examined the potential for healthy lifestyle and behavioural changes to improve placental growth, development, and function. While the placenta represents the critical maternal-fetal interface responsible for all gas, nutrient, and waste exchange between the mother and fetus, the impact of exercise during pregnancy on placental biology and function is not well known. This review will focus on prenatal exercise and its promising influence on the structures of the maternal-fetal interface, with particular emphasis on the placenta. Potential molecular mechanistic hypotheses are presented to aid future investigations of prenatal exercise and placental health.

Maternal physiological changes at rest induced by exercise during pregnancy: A randomized controlled trial

OBJECTIVE

to analyse maternal physiological changes in several areas (cardiovascular, metabolic, renal and hepatic) related to the regular practice of a supervised exercise program.

METHODS

This is an unplanned secondary analysis from a randomized controlled trial carried out in a single maternity unit in Madrid, Spain (NCT 02,756,143). From November 2014 to June 2015, 92 women were randomly assigned to perform a mild-moderate supervised exercise program during pregnancy (Intervention group, IG) or to continue with their routine pregnancy care (control group, CG). For the purpose of this study we collected clinical and analytical data (heart blood pressure, weight, blood glucose, AST, ALT, blood Creatinine and blood Uric acid) available from all obstetric visits and examined the differences between groups.

RESULTS

We did not find any differences in: pregnancy weight (IG: 11.4 ± 4.4 Kg vs. CG: 10.1 ± 5.3 Kg; p = 0.173); fasting glucose at 10⁺⁰-12⁺⁶ weeks (IG: 78.48±8.34 vs. CG: 76±13.26, p = 0.305) or at 34⁺⁰-36⁺⁴ weeks (IG: 73.25±10.27 vs CG: 73.45± 8.29,p = 0.920), and 50 gs glucose tolerance at 24⁺⁴-26⁺⁶weeks (IG: 116.23±35.07 vs CG: 116.36±25.98, p = 0.984); Aspartate-amino-transferase at 10⁺⁰-12⁺⁶ weeks (IG: 15.38±4.17 vs CG: 17.33±7.05, p = 0.124) and at 34⁺⁰-36⁺⁴ weeks (IG: 21.65±5.25 vs CG: 19.53±8.32, p = 0.165) or Alanine-amino- transferase at 10⁺⁰-12⁺⁶ weeks (IG: 27.50±10.63 vs CG: 28.27±11.77, p = 0.746) or at 34⁺⁰-36⁺⁴ weeks (IG: 22.93±9.23 vs CG: 20.84±13.49, p = 0.407); blood Creatinine concentrations at 34⁺⁰-36⁺⁴ weeks (IG: 0.595±0.401 vs CG: 0.575±0.100, p = 0.757) and blood uric acid concentrations at 34⁺⁰-36⁺⁴ weeks (IG: 3.526 ± 0.787 vs CG: 3.262±0.672, p = 0.218). Heart blood pressure was similar between groups except at 27⁺⁰-28⁺⁶ weeks, where systolic blood pressure was significantly lower in the CG in comparison to the IG (116.31±10.8 mmHg vs. 120.22 ± 10.3 mmHg, p = 0.010).

CONCLUSION

Regular supervised exercise during pregnancy does not alter normal maternal physiology.

Effects of prenatal exercise on fetal heart rate, umbilical and uterine blood flow: a systematic review and meta-analysis

OBJECTIVE

To perform a systematic review and meta-analysis examining the influence of acute and chronic prenatal exercise on fetal heart rate (FHR) and umbilical and uterine blood flow metrics.

DESIGN

Systematic review with random-effects meta-analysis and meta-regression.

DATA SOURCES

Online databases were searched up to 6 January 2017.

STUDY ELIGIBILITY CRITERIA

Studies of all designs were included (except case studies) if published in English, Spanish or French, and contained information on the population (pregnant women without contraindication to exercise), intervention (subjective or objective measures of frequency, intensity, duration, volume or type of exercise, alone ["exercise-only"] or in combination with other intervention components [eg, dietary; "exercise + co-intervention"]), comparator (no exercise or different frequency, intensity, duration, volume and type of exercise) and outcomes (FHR, beats per minute (bpm); uterine and umbilical blood flow metrics (systolic:diastolic (S/D) ratio; Pulsatility Index (PI); Resistance Index (RI); blood flow, mL/min; and blood velocity, cm/s)).

RESULTS

'Very low' to 'moderate' quality evidence from 91 unique studies (n=4641 women) were included. Overall, FHR increased during (mean difference (MD)=6.35bpm; 95% CI 2.30 to 10.41, I²=95%, p=0.002) and following acute exercise (MD=4.05; 95% CI 2.98 to 5.12, I²=83%, p<0.00001). The incidence of fetal bradycardia was low at rest and unchanged with acute exercise. There were no significant changes in umbilical or uterine S/D, PI, RI, blood flow or blood velocity during or following acute exercise sessions. Chronic exercise decreased resting FHR and the umbilical artery S/D, PI and RI at rest.

CONCLUSION

Acute and chronic prenatal exercise do not adversely impact FHR or uteroplacental blood flow metrics.

Associations between prenatal physical activity, birth weight, and DNA methylation at genomically imprinted domains in a multiethnic newborn cohort

Birth weight is a commonly used indicator of the fetal environment and a predictor of future health outcomes. While the etiology of birth weight extremes is likely multifactorial, epidemiologic data suggest that prenatal physical activity (PA) may play an important role. The mechanisms underlying this association remain unresolved, although epigenetics has been proposed. This study aimed to estimate associations between prenatal PA, birth weight, and newborn DNA methylation levels at differentially methylated regions (DMRs) regulating 4 imprinted genes known to be important in fetal development. Study participants (N = 1281) were enrolled as part of the Newborn Epigenetics Study. Prenatal PA was ascertained using the Pregnancy Physical Activity Questionnaire, and birth weight data obtained from hospital records. Among 484 term mother-infant pairs, imprinted gene methylation levels were measured at DMRs using bisulfite pyrosequencing. Generalized linear and logistic regression models were used to estimate associations. After adjusting for preterm birth and race/ethnicity, we found that infants born to mothers in the highest quartile of total non-sedentary time had lower birth weight compared to infants of mothers in the lowest quartile (β = -81.16, SE = 42.02, P = 0.05). These associations appeared strongest among male infants (β = -125.40, SE = 58.10, P = 0.03). Methylation at the PLAGL1 DMR was related to total non-sedentary time (P < 0.05). Our findings confirm that prenatal PA is associated with reduced birth weight, and is the first study to support a role for imprinted gene plasticity in these associations. Larger studies are required.

Placental and vascular adaptations to exercise training before and during pregnancy in the rat

Although exercise during pregnancy is generally recommended and thought to be beneficial to mother and fetus, the nature of the adaptations to exercise during pregnancy and how they may be beneficial remain poorly understood. Recent studies suggest that exercise may stimulate expression of several cytoprotective and pro-angiogenic molecules such as heat shock proteins (HSP) and vascular endothelial growth factors (VEGF). We hypothesized that exercise training during pregnancy improves angiogenic balance, increases HSP expression, and improves endothelial function. Female rats were given access to an exercise wheel for 6 wk before and during pregnancy. On day 19 of pregnancy tissues were collected and snap frozen for later analysis. Western blots were performed in skeletal muscle and placenta. HSP 27 (3.7 ± 0.36 vs. 2.2 ± 0.38; P < 0.05), HSP 60 (2.2 ± 0.73 vs. 0.49 ± 0.08; P < 0.05), and HSP 90 (0.33 ± 0.09 vs. 0.11 ± 0.02; P < 0.05) were increased in the placentas of exercise-trained rats compared with sedentary controls. In addition, exercise training increased (P < 0.05) plasma free VEGF and augmented (P < 0.05) endothelium-dependent vascular relaxation compared with nonexercise control rats. The present data indicates chronic exercise training stimulates HSP expression in the placenta and that regular exercise training increases circulating VEGF in pregnant but not in nonpregnant rats. Although the present findings suggest that exercise before and during pregnancy may promote the expression of molecules that could attenuate placental and vascular dysfunction in complicated pregnancies, further studies are needed to determine the safety and effectiveness of exercise training as a therapeutic modality in pregnancy.

A prospective study of the association between vigorous physical activity during pregnancy and length of gestation and birthweight

Current US pregnancy-related physical activity recommendations do not provide specific guidance for vigorous intensity activity. We examined the associations between vigorous physical activity during pregnancy and length of gestation and birthweight.

METHODS

Women were recruited before 10 weeks gestation. At 13-16 weeks gestation, participants reported the type, frequency, and duration of their typical weekly vigorous physical activities. Activity domains included recreational, occupational, household, and child/adult care. Infant birth date was obtained from medical or vital records; if unavailable, self-report was used. Birthweight (from vital records) was studied among term births. We analyzed gestational age among 1,647 births using discrete-time survival analysis. We used logistic and linear regression to analyze preterm birth (birth at <37 weeks) and birthweight, respectively. Vigorous recreational activity was associated with longer gestation (any vs. none, hazard ratio (HR) [95% CI]: 0.85 [0.70, 1.05]) and we did not detect any dose-response association. Higher frequency of vigorous recreational activity sessions (adjusted for total volume of activity) was associated with a decreased odds of preterm birth (≥ 4 sessions/week vs. 0 or 1, OR [95% CI]: 0.08 (0.006, 1.0). Birthweight was not associated with physical activity measures. In summary, vigorous physical activity does not appear to be detrimental to the timing of birth or birthweight. Our data support a reduced risk of preterm birth with vigorous recreational activity, particularly with increased frequency of recreational activity sessions. Future studies should investigate the components of physical activity (i.e., intensity, duration, and frequency) in relation to birth outcomes.

Maternal Recreational Exercise during Pregnancy in relation to Children's BMI at 7 Years of Age

Exposures during fetal life may have long-term health consequences including risk of childhood overweight. We investigated the associations between maternal recreational exercise during early and late pregnancy and the children's body mass index (BMI) and risk of overweight at 7 years. Data on 40,280 mother-child pairs from the Danish National Birth Cohort was used. Self-reported information about exercise was obtained from telephone interviews around gestational weeks 16 and 30. Children's weight and height were reported in a 7-year follow-up and used to calculate BMI and overweight status. Data was analyzed using multiple linear and logistic regression models. Recreational exercise across pregnancy was inversely related to children's BMI and risk of overweight, but all associations were mainly explained by smoking habits, socioeconomic status, and maternal pre-pregnancy BMI. Additionally, we did not find exercise intensity or changes in exercise habits in pregnancy related to the children's BMI or risk of overweight.

Physical exercise during pregnancy and fetal growth measures: a study within the Danish National Birth Cohort

OBJECTIVE

The objective of the study was to examine the association between physical exercise during pregnancy and fetal growth measures.

STUDY DESIGN

Data on 79,692 liveborn singletons from the Danish National Birth Cohort were collected between 1996 and 2002. Mean differences in birthweight, length, ponderal index, head and abdominal circumference, and placental weight and hazard ratios of small- and large-for-gestational-age babies were calculated.

RESULTS

Our data indicated smaller babies in exercising women compared with nonexercisers, but the differences were small, and only a few were statistically significant. Exercising women had a slightly decreased risk of having a child small for gestational age (hazard ratio, 0.87; 95% confidence interval, 0.83-0.92) and large for gestational age (hazard ratio, 0.93; 95% confidence interval, 0.89-0.98).

CONCLUSION

The findings do not indicate sizable effects on fetal growth measures related to exercise apart from a modest decreased risk of small- and large-for-gestational-age infants. These findings do not speak against advising pregnant women to be physically active during pregnancy.

Avaliação do efeito do exercício físico no metabolismo de ratas diabéticas prenhes

O objetivo deste estudo foi verificar se a prática do exercício físico (natação), iniciada em diferentes momentos da prenhez de ratas diabéticas, promove alterações no metabolismo materno. Após confirmação do diabete, induzido por Streptozotocin, ratas Wistar foram acasaladas e randomizadas em três grupos (n = 13 ratas/grupo): não-praticante (G1) ou praticante de exercício desde o dia zero (G2) ou sétimo dia (G3) de prenhez. O exercício consistiu de um programa de natação com intensidade moderada. Durante a prenhez, glicemia e peso corpóreo foram avaliados semanalmente. No final da prenhez, as ratas foram anestesiadas e dessangradas para obtenção de amostras de sangue para determinação de proteínas totais, triglicérides, colesterol total e VLDL-colesterol. Fígado e músculo foram coletados para dosagem de glicogênio hepático e muscular, respectivamente. Independente do momento em que foi iniciado, o exercício não alterou os níveis glicêmicos, a evolução do peso corpóreo e as concentrações de proteínas totais e glicogênio hepático e muscular. Porém, a natação iniciada no sétimo dia de prenhez diminuiu as taxas de triglicérides (G1 = 369,10 ± 31,91mg/dL; G2 = 343,32 ± 162,12mg/dL; G3 = 212,35 ± 70,32mg/dL), colesterol total (G1 = 176,48 ± 28,25mg/dL; G2 = 141,33 ± 19,77mg/dL; G3 = 129,86 ± 33,16mg/dL) e VLDL (G1 = 64,92 ± 24,41mg/dL; G2 = 63,54 ± 28,31mg/dL; G3 = 42,53 ± 14,12mg/dL) comparando com o grupo G1. Apesar de não se comprovar a influência do exercício físico sobre os níveis glicêmicos maternos, a prática diária de natação a partir do sétimo dia de prenhez mostrou-se benéfica para o perfil lipídico de ratas diabéticas. Esse resultado reforça a validade da associação da atividade física regular à dieta e insulina na gestação complicada pelo diabete.

Effects of Pregnancy on Maternal Work Tolerance

This review summarizes current information on the tolerance of healthy pregnant women and their fetuses to acute strenuous exertion. Maximal aerobic power, expressed in L•min−1, is not significantly affected in women who maintain an active lifestyle, whereas values expressed in mlùkg−1ùmin−1 decline with advancing gestational age in relation to maternal/fetal weight gain. Efficiency during standard exercise testing and the ventilatory anaerobic threshold (Tvent) also appear to be unaffected by pregnancy, but the ability to utilize carbohydrate and exercise anaerobically during brief strenuous exercise may be reduced. Fetal responses to short strenuous exercise are usually moderate and revert to baseline values within approximately 30 min postexercise. Future studies should examine alveolar gas exchange kinetics at the start of exercise and during recovery from both moderate and strenuous exertion. Existing studies of the responses of pregnant women to prolonged exercise have focused primarily on substrate utilization and glucose homeostasis. Other maternal responses to prolonged exercise that should be examined include acid-base regulation, temperature regulation, fluid and electrolyte balance, and perception of effort. Fetal reactions should also be examined in relation to maternal responses. Until evidence-based, occupation-specific guidelines become available, it is recommended that pregnant women use the Joint SOGC/CSEP Clinical Practice Guideline: Exercise in Pregnancy and the Postpartum Period, published by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology (2003). Key words: human gestation, maximal exercise, prolonged exercise, fetal well-being