Mechanisms for blood pressure reduction following isometric exercise training: a systematic review and meta-analysis

Abstract

Isometric exercise training (IET) is established as an effective antihypertensive intervention. Despite this, the physiological mechanisms driving blood pressure (BP) reductions following IET are not well understood. Therefore, we aimed to perform the first meta-analysis of the mechanistic changes measured following IET.Methods: PubMed, Cochrane library and SPORTDiscus were systematically searched for randomized controlled trials published between January 2000 and December 2021 reporting the effects of IET on resting BP and at least one secondary mechanistic parameter following a shortterm intervention (2-12 weeks).Results: Eighteen studies with a pooled sample size of 628 participants were included in the final analysis. IET produced significant reductions in resting systolic and diastolic BP of 9.35 mmHg (95% confidence interval [CI] ¼ À 7.80 to À10.89, P < 0.001) and 4.30 mmHg (CI ¼ À3.01 to À5.60, P < 0.001), respectively. Mechanistically, IET produced a statistically significant reduction in resting heart rate (mean difference [MD]: À1.55 bpm, CI ¼ À0.14 to À2.96, P ¼ 0.031) and a significant increase in stroke volume (MD: 6.35 ml, CI ¼ 0.35 to 12.60, P ¼ 0.038), with no significant change in cardiac output. Conversely, total peripheral resistance (TPR) significantly decreased following IET (MD: À100.38 dyne s À1 cm 5 , CI ¼ À14.16 to À186.61, P ¼ 0.023), with significant improvements in the low frequency to high frequency heart rate variability ratio (MD: À0.41, CI ¼ À0.09 to À0.73, P ¼ 0.013) and baroreceptor reflex sensitivity (MD: 7.43 ms/mmHg, P < 0.001). Conclusion:This work demonstrates that a reduction in TPR, potentially mediated through enhanced autonomic vasomotor control, is primarily responsible for BP reductions following IET. Furthermore, this novel analysis suggests wall squat interventions to be the most effective IET mode, with clinically relevant differences in BP reductions compared to handgrip and leg extension IET; although future direct comparative research is required.

Reductions in systolic blood pressure achieved by hypertensives with three isometric training sessions per week are maintained with a single session per week

“…This is an important consideration as the burden of hypertension and other cardiometabolic disease is larger in LMIC than in high income countries. 2 Based on our findings and other recent evidence, 10 , 17 the wall squat appears to therefore provide the best cost‐benefit in BP in hypertensives and is well tolerated, well adhered to and with no reports of adverse events in the present or previous wall squat interventions. Indeed, no dropouts and a 77% compliance with exercise sessions was reported in a recent year‐long‐wall squat intervention.…”

“…However, after phase 2, during which training frequency was reduced to 1 session per week, in the handgrip group SBP increased by .5 mmHg, while there was a further 1.8 mmHg decline in the wall squat group, representing a small magnitude but clinically relevant 3.8 mmHg greater SBP reduction in the wall squat group over the whole intervention–which aligns with the estimated >3 mmHg difference favoring wall squat over handgrip training in a recent meta‐analysis. 17 …”

“…The present study is the first to examine whether reductions achieved with the standard three times per week intervention can be retained with a reduced training frequency or “maintenance dose.” While a weekly single session of wall squat exercise not only maintains, but potentially continues to promote SBP reductions, handgrip exercise begins to show a reversal of gains and may require a higher frequency to sustain the benefits achieved. The larger muscle mass recruited and therefore area of vascular occlusion during the wall squat exercise 17 might explain its ability to maintain adaptations at a lower frequency of training.…”

“…Changes in cardiovascular function including significantly decreased heart rate and increased stroke volume (with stable cardiac output) are also consistently reported. 17 …”

Exercise prescription in the treatment of hypertension

“…This exercise should be performed at an intensity of 50% of maximum oxygen intake. Moreover, a meta-analysis has shown that resistance exercise also has antihypertensive effects [2]. A reduction in total peripheral resistance, potentially mediated by enhanced autonomic vasomotor control, is the primary cause of blood pressure (BP) reductions following isometric exercise.…”