Isometric exercise training and blood pressure control: exploring the dose-response to training frequency in a randomised controlled trial.

Background: Isometric exercise training (IET) is a time-efficient intervention that consistently demonstrates clinically meaningful reductions in resting blood pressure (BP). The optimal frequency required to maintain these benefits has not been established. This study aimed to (1) examine the dose-response relationship between training frequency and the maintenance of BP reductions following an initial 4-week IET period and (2) investigate the physiological mechanisms underpinning any observed changes in BP. Methods: Adults (n=100) with normal to high-normal BP were randomised into five groups: 3×, 2×, 1× or 0× IET sessions/week following an initial 4-week lower-body IET protocol (3×/week), or control. Haemodynamic and cardiac autonomic variables, including resting BP, total peripheral resistance (TPR), heart rate variability (HRV) and baroreceptor reflex sensitivity (BRS) were assessed at baseline, following the initial intervention (week 4), and following the maintenance period (week 8). Results: All intervention groups showed significant reductions in systolic BP (sBP), diastolic BP and mean arterial pressure (MAP) after 4 weeks compared with control (-9.45±6.69 mm Hg, p<0.001, -5.47±9.92 mm Hg, p=0.007 and -6.80±7.77 mm Hg, p<0.001, respectively). At week 8, the 1×, 2× and 3×/week groups maintained sBP and MAP reductions, although the magnitude of these reductions was significantly greater in the 3×/week group (p<0.001). The 0×/week group showed reversal of BP reductions to levels not significantly different from control. Only the 3×/week group maintained improvements in TPR, HRV and BRS. Conclusions: A reduction in IET frequency to 1-2 sessions per week can partially attenuate the rate at which BP adaptations regress during short-term reductions in training frequency.