Acute fetal response to high-intensity interval training in the second and third trimesters of pregnancy

Interval training and cardiometabolic health in reproductive-aged females

Physical activity and exercise training are especially important for reproductive-aged females as exercise-induced health benefits can also affect their infants. However, levels of physical inactivity remain high among females in this age group, before, during, and after pregnancy. There is a great need for practical and feasible exercise modes to increase adherence to exercise in this population, and interval training may be a time-efficient training modality. Interval training is a form of exercise involving intermittent bouts of intense effort interspersed with recovery periods of rest or lower-intensity exercise. A substantial amount of research indicates that interval training induces superior cardiometabolic health benefits compared with iso-energetic moderate-intensity continuous exercise. This review provides a comprehensive overview of research on interval training interventions in reproductive-aged females across various life stages, focusing on the cardiometabolic health benefits. We discuss the potential role of interval training in premenopausal females with overweight/obesity, polycystic ovary syndrome, and subfertility, as well as the potential influence of oral contraceptives on cardiometabolic adaptations to interval training. Furthermore, this review also highlights recent findings supporting the beneficial role of high-intensity interval training for cardiometabolic health outcomes during pregnancy. In summary, the existing evidence suggests that interval training can improve several cardiometabolic and reproductive outcomes in females spanning different life stages. However, more research is needed to further strengthen the evidence-base for physical activity recommendations for females in their reproductive years of life.

Maternal and Fetal Cardiovascular Responses to Acute High-Intensity Interval and Moderate-Intensity Continuous Training Exercise During Pregnancy: A Randomized Crossover Trial

OBJECTIVE

We aimed to compare maternal and fetal cardiovascular responses to an acute bout of high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) during pregnancy.

METHODS

Fifteen women with a singleton pregnancy (27.3 ± 3.5 weeks of gestation, 33 ± 4 years of age) were recruited. Following a peak fitness test, participants engaged in a session of HIIT (10 × 1-min intervals ≥ 90% maximum heart rate [HRmax]) interspersed with 1 min of active recovery) and MICT (30 min at 64-76% HRmax) 48 h apart in random order. Maternal HR, blood pressure, middle (MCAv), and posterior cerebral artery blood velocity (PCAv), as well as respiratory measures were monitored continuously throughout HIIT/MICT. Fetal heart rate, as well as umbilical systolic/diastolic (S/D) ratio, resistive index (RI), and pulsatility index (PI) were assessed immediately before and after exercise.

RESULTS

Average maternal heart rate was higher for HIIT (82 ± 5% HRmax) compared with MICT (74 ± 4% HRmax; p < 0.001). During the HIIT session, participants achieved a peak heart rate of 96 ± 5% HRmax (range of 87-105% HRmax). Maternal cerebral blood velocities increased with exercise but was not different between HIIT and MICT for MCAv (p = 0.340) and PCAv (p = 0.142). Fetal heart rate increased during exercise (p = 0.244) but was not different between sessions (HIIT: Δ + 14 ± 7 bpm; MICT: Δ + 10 ± 10 bpm). Metrics of umbilical blood flow decreased with exercise and were not different between exercise sessions (PI: p = 0.707; S/D ratio: p = 0.671; RI: p = 0.792). Fetal bradycardia was not observed, and S/D ratio, RI, and PI remained within normal ranges both before and immediately after all exercise sessions.

CONCLUSIONS

An acute bout of HIIT exercise consisting of repeated 1-min near-maximal to maximal exertions, as well as MICT exercise is well tolerated by both mother and fetus.

CLINICAL TRIAL REGISTRATION

NCT05369247.

Effects of 8-Week Online, Supervised High-Intensity Interval Training on the Parameters Related to the Anaerobic Threshold, Body Weight, and Body Composition during Pregnancy: A Randomized Controlled Trial

We aimed to assess the effects of an 8-week, online high-intensity interval training (HIIT) program on the parameters related to the anaerobic threshold (AT), body weight, and body composition in pregnant women. A total of 69 Caucasian women with an uncomplicated singleton pregnancy (age: 31 ± 4 years; gestational age: 22 ± 5 weeks; mean ± standard deviation) were randomly allocated to either an 8-week HIIT program (HIIT group) or to a comparative 8-week educational program (EDU group). Our most important finding was that even with the 8-week progression of pregnancy and physiological weight gain, the HIIT group maintained the same level of parameters related to AT: volume of oxygen at the AT (VO2/AT), percentage of maximal oxygen uptake at the AT (%VO2max/AT), and heart rate at the AT (HR/AT). In contrast, in the EDU group we observed a substantial deterioration of parameters related to the AT. The HIIT intervention substantially reduced the fat mass percentage (median: 30 to 28%; p < 0.01) and improved the total fat-free mass percentage (median: 70% to 72%; p < 0.01). In the EDU group, the body composition did not change significantly. An online, supervised HIIT program may be used to prevent the pregnancy-related risk of excessive weight gain and reduction in exercise capacity without yielding adverse obstetric or neonatal outcomes.

Glycemic response to acute high-intensity interval versus moderate-intensity continuous exercise during pregnancy

The present study investigated the glycemic response to an acute high-intensity interval training (HIIT) session (10 one-minute intervals ≥90% HRmax interspersed with one-minute of active recovery) versus a moderate-intensity continuous training (MICT) session (30 min at 64%-76% HRmax ) during pregnancy. Twenty-four normoglycemic females with a singleton pregnancy (27.8 ± 4.7 weeks of gestation, 31.5 ± 4.1 years of age, body mass index: 25.2 ± 11.3) participated in a randomized crossover design study. A flash glucose monitor and accelerometer were worn continuously for 7 days recording glycemic response, physical activity, and sleep. Nutritional intake and enjoyment of the exercise were self-reported. Average heart rate during exercise was higher for HIIT (82 ± 4% HRmax ) compared with MICT (74 ± 4% HRmax ; p < 0.001) and participants achieved a peak heart rate of 92 ± 3% during HIIT (range 85%-97% HRmax ) compared with 81 ± 4% during MICT (p < 0.001). The change in glucose values from pre-to-postexercise were not different between conditions (HIIT: -0.62 ± 1.00 mmol/L; MICT: -0.81 ± 1.05 mmol/L; p = 0.300) with the exception that fewer individuals experienced postexercise hypoglycemia immediately following HIIT compared with MICT (8% versus 33% respectively; p = 0.041). Other glucose variables was not different between exercise protocols. Physical activity (p = 0.07) and caloric intake did not differ (p = 0.10). The majority of participants preferred HIIT (87.5%) and had greater perceived enjoyment compared to MICT (HIIT: 7.8 ± 1.5; MICT: 6.6 ± 2.0; p = 0.015). Sleep duration was 52 ± 73 min longer after participating in HIIT compared with the night prior (main effect for time p = 0.017); no significant changes for MICT. Overall, an acute session of HIIT appears to be well tolerated and demonstrates no adverse effects on maternal glycemic response.

Performance-Related Physiological and Haematological Changes During Pregnancy and Postpartum in a Well-Trained Cyclist Performing Endurance Training

Purpose: To describe the performance-related physiological and haematological changes in a well-trained cyclist (peak oxygen uptake, VO2peak: 54.9 ml min-1·kg-1) performing endurance training during pregnancy and postpartum. Methods: Training data was systemized by training form (endurance and resistance), intensity (low- (LIT), moderate-, and high-intensity training), and modality (cycling, running, hiking, XC-skiing, strength training and other). Power output at 4 mmol L-1 [BLa-] (L4), maximal aerobic power (Wmax), and VO2peak as well as haemoglobin mass, blood volume, plasma volume and red blood cell volume (RBCV) were measured at different time points during pregnancy and 12 weeks postpartum. Results: L4 and Wmax increased by 3% while absolute VO2peak was unaltered from gestational wk 2 to 14, despite 12 and 14% increases in RBCV and BV. After delivery, BV was reduced by 7% but RBCV was maintained 5% above start-pregnancy levels, while VO2peak almost returned to (-1%), and Wmax increased by 5% above start-pregnancy levels 12 weeks postpartum. Conclusion: This case-study illustrates a disassociation between increases in haematological values and VO2peak during pregnancy. Furthermore, a quick resumption of LIT and a gradually increasing intensity of training in the 12 weeks following delivery ensured a return to start-pregnancy levels of VO2peak and corresponding improvements in Wmax. Although general recommendations cannot be given on the basis of these data, this study provides a framework for investigating pregnant endurance athletes and contributes to the generation of new hypotheses in this field.

Evaluating Evidence-Based Content, Features of Exercise Instruction, and Expert Involvement in Physical Activity Apps for Pregnant Women: Systematic Search and Content Analysis

Background

Guidelines for physical activity and exercise during pregnancy recommend that all women without contraindications engage in regular physical activity to improve both their own health and the health of their baby. Many women are uncertain how to safely engage in physical activity and exercise during this life stage and are increasingly using mobile apps to access health-related information. However, the extent to which apps that provide physical activity and exercise advice align with current evidence-based pregnancy recommendations is unclear.

Objective

This study aims to conduct a systematic search and content analysis of apps that promote physical activity and exercise in pregnancy to examine the alignment of the content with current evidence-based recommendations; delivery, format, and features of physical activity and exercise instruction; and credentials of the app developers.

Methods

Systematic searches were conducted in the Australian App Store and Google Play Store in October 2020. Apps were identified using combinations of search terms relevant to pregnancy and exercise or physical activity and screened for inclusion (with a primary focus on physical activity and exercise during pregnancy, free to download or did not require immediate paid subscription, and an average user rating of ≥4 out of 5). Apps were then independently reviewed using an author-designed extraction tool.

Results

Overall, 27 apps were included in this review (Google Play Store: 16/27, 59%, and App Store: 11/27, 41%). Two-thirds of the apps provided some information relating to the frequency, intensity, time, and type principles of exercise; only 11% (3/27) provided this information in line with current evidence-based guidelines. Approximately one-third of the apps provided information about contraindications to exercise during pregnancy and referenced the supporting evidence. None of the apps actively engaged in screening for potential contraindications. Only 15% (4/27) of the apps collected information about the user’s current exercise behaviors, 11% (3/27) allowed users to personalize features relating to their exercise preferences, and a little more than one-third provided information about developer credentials.

Conclusions

Few exercise apps designed for pregnancy aligned with current evidence-based physical activity guidelines. None of the apps screened users for contraindications to physical activity and exercise during pregnancy, and most lacked appropriate personalization features to account for an individual’s characteristics. Few involved qualified experts during the development of the app. There is a need to improve the quality of apps that promote exercise in pregnancy to ensure that women are appropriately supported to engage in exercise and the potential risk of injury, complications, and adverse pregnancy outcomes for both mother and child is minimized. This could be done by providing expert guidance that aligns with current recommendations, introducing screening measures and features that enable personalization and tailoring to individual users, or by developing a recognized system for regulating apps.