Cardiac Autonomic Function and Baroreflex Changes Following 4 Weeks Resistance Versus Aerobic Training in Pre Hypertensives

Abstract

INTRODUCTION: Cardiac autonomic modulation and baroreflex sensitivity (BRS) are altered in individuals with hypertension. Aerobic exercise (AE) training has been shown to improve both measures, yet little is known about the effects of resistance exercise (RE). The purpose of this study was to examine heart rate variability (HRV) and baroreflex sensitivity (BRS) following 4 weeks of resistance or aerobic training in a population with high blood pressure. METHODS: Twenty-nine pre or mild hypertensives (20 males and 9 females) who were not taking any medications were recruited (Age= 48±1 yrs, systolic blood pressure (SBP) 139±2 mmHg, diastolic blood pressure (DBP) 79±1 mmHg) and randomly assigned to 4-weeks of RE (3 sets of 8 repetitions at 65% of 10RM, 3 days/week) or AE (30 minutes treadmill exercise at 65% VO2max, 3 days/week) training. Before and after training resting measures of HRV frequencies (low frequency (LF); high frequency (HF); LFHF ratio; total power (TP) and BRS were obtained. Data are presented as mean±SE. RESULTS: There was a significant decrease in resting SBP for both training modes (RE 136±3.0 pre to 132±3.4 post vs. AE 142±4.0 pre to 137±3.6 mm Hg post training, p=0.019). Also, DBP decreased significantly following both modes (RE 78±1.31 pre to 74±1.1 post vs. AE 80±1.7 pre to 77±1.6 mm Hg post, p=0.002). A significant time by mode interaction for LFHF ratio (p=0.017) with AE decreasing the ratio (275.21±67.28 to 161.26±61.49) and RE increasing this ratio (143.73±65.00 to 227.83±59.41). Natural log transformed values showed a time-by-mode interaction for lnHF (p = 0.05) as lnHF increased (4.7±0.38 to 5.4±0.35 ms2) following AE and decreased (5.98±0.37 to 5.76±0.42 ms2) following RE. BRS increased following aerobic training and decreased after resistance training (6.74±1.2 to 7.94±1.3 and 10.44±1.2 to 9.1±1.2 ms/mmHg respectively, p=0.021) CONCLUSIONS: Four weeks of AE training led to improvements of the autonomic nervous system by increasing vagal tone, and reducing the sympathovagal balance while increasing BRS in hypertensives. RE showed no improvements in cardiac autonomic tone yet decreased BRS. This suggests that aerobic training may be more beneficial in altering cardiac autonomic modulation than resistance training for individuals with pre-hypertension.