Fetal Heart Rate During Moderate To High Intensity Resistance Exercise In Pregnant Individuals

Fetal heart rate (FHR) is an indicator of fetal stress during pregnancy and has been observed following high intensity aerobic training (>90%Vo2max), but the effects of resistance training are relatively unknown. PURPOSE: The purpose of this study was to investigate a progressive resistance exercise program on FHR. It was hypothesized that FHR would stay below the 160 beats per minute (BPM) threshold at intensities up to 85% max. A second exploratory aim was to compare FHR response between physically active and sedentary pregnant individuals to determine if training status influences degree of change during exercise. METHODS: Healthy pregnant women between 28-32 weeks gestation were recruited and attended three visits over two weeks. The first two visits involved completing a physical activity questionnaire, undergoing exercise familiarization, and then performing 8-RM tests on each of the following exercises: squat, incline bench, deadlift (DL), lat pull down (LPD), leg press (LP), and seated row. On Visit 3, participants performed 3 sets of 8 repetitions for each exercise progressing from 50% 8RM, 75% 8RM, to 85% 8RM each set. MHR and FHR were recorded during a 2 minute rest between sets. Descriptive statistics, Shaprio-Wilk normality tests, and MANOVAS were used to analyze the data and compare groups. RESULTS: Thirty pregnant women participated in the study (31.8 ± 4 yo, pre-pregnancy BMI 24.6 ± 5.5). Among all participants maximal FHR averaged 156.2 BPM ± 8.3, 90% CI [153.9-158.5 BPM]. FHR was >160 BPM 15 times (5 after the LPD, 6 after the row, 3 after the DL and 1 after the LP) with 87% of the occurrences at ≥75% intensity. Sixteen participants were frequent exercisers (>150 min MVPA/wk) who had lower resting MHR (p = 0.063), and lower FHR change during the squat (p = 0.060) and the LPD (p = 0.058) compared to the 14 inactive participants (<90 min MVPA/wk). CONCLUSION: Fetal heart rate can exceed 160 BPM following resistance exercise ≥75% max but is transient and returns to normal levels in the two minutes following exercise cessation. The LPD and row exercise appear to cause greater increases in FHR, possibly due to the increased intrathoracic and intraabdominal pressure produced by the exercise. Participants who remained active during pregnancy demonstrated better cardiovascular dynamics in response to exercise. ACSM Foundation Doctoral Student Research Grant from the American College of Sports Medicine