Isometric handgrip exercise training reduces resting systolic blood pressure but does not interfere with diastolic blood pressure and heart rate variability in hypertensive subjects: a systematic review and meta-analysis of randomized clinical trials

To evaluate the effects of isometric handgrip exercise training (IHET) on blood pressure and heart rate variability in hypertensive subjects. Five databases were searched for randomized clinical trials in English, Spanish, or Portuguese evaluating the effect of IHET vs. no exercise on blood pressure (systolic and/or diastolic) and/or heart rate variability (low frequency [LF], high frequency [HF], and/or LF/HF ratio) through December 2020. Random-effects meta-analyses of mean differences (MDs) and/or standardized mean differences (SMDs) with 95% confidence intervals (CIs) were performed. Five trials were selected (n = 324 hypertensive subjects), whose durations ranged from 8 to 10 weeks. Compared to no exercise, IHET reduced systolic blood pressure (MD -8.11 mmHg, 95% CI -11.7 to -4.53, p < 0.001) but did not affect diastolic blood pressure (MD -2.75 mmHg, 95% CI -9.47-3.96, p = 0.42), LF (SMD -0.14, 95% CI -0.65-0.37, p = 0.59), HF (SMD 0.38, 95% CI -0.14-0.89, p = 0.15), or the LF/HF ratio (SMD -0.22, 95% CI -0.95-0.52, p = 0.57). IHET performed for 8-10 weeks had a positive effect on resting systolic blood pressure but did not interfere with diastolic blood pressure or heart rate variability in hypertensive subjects. These data should be interpreted with caution since all volunteers included in the studies were clinically medicated and their blood pressure was controlled.