Cardiovascular Responses to Isometric Resistance Training in Individuals with Hypertension, to aid in Blood Pressure Management

Abstract

<b>Background</b> Hypertension is a major risk factor contributing to cardiovascular disease; including coronary artery disease, stroke and heart failure. The recent U.S. National Health and Nutrition Examination Survey indicates that >50% of cardiovascular deaths in the US occurred in individuals with hypertension. Antihypertensive medications are effective in controlling blood pressure and have minimal side effects; however, only half the people with hypertension reach treatment goals. Current first line treatment for hypertension is non-pharmacological lifestyle modification including healthy eating, smoking cessation and increasing physical activity. Recent research indicates that isometric resistance training may elicit blood pressure reductions greater than those seen with dynamic aerobic and resistance exercise. <br/> <b>Methods</b> In order to determine our research direction, a meta-analysis was conducted of previous isometric studies. The meta-analysis in chapter 2 was conducted to determine characteristics of patients conducting isometric resistance training (IRT) and the current protocols being utilised. The systematic review conducted for the meta-analysis indicated gaps in the literature pertaining to study sample sizes, with the largest study having 36 participants; and duration, as the majority of studies were for 8 weeks. The meta-analysis also indicated that, although 2 studies utilised a low intensity group, either a sedentary control or no control group was used for all studies. <br/> Based on this, we initially conducted an IRT study using high and sham/low intensity groups for eight weeks to look at the efficacy of IRT in blood pressure management. The primary aim of this study was to address the gap in the literature relating to the use of a sham low intensity group as a working control. Previous studies had predominantly had participants who were either < 35 years or > 60 years, there were a few studies that had participants aged between 45 and 60 years; we recruited participants aged between 35 and 65 to address this gap in the literature. <br/> A second study was conducted with a duration of 12 weeks, the longest published study to date. At the time of conducting my research there were no published IRT studies which had utilised 24 hour ambulatory blood pressure monitoring, so this used to address the gap in the literature. No studies had determined the detraining effect of IRT so I had participants return 12 weeks after completing the exercise protocol to determine the detraining effect. <br/> Another randomized trial was conducted to determine hypertensive responses, including peak rate pressure product (RPP) during isometric handgrip exercise. Concerns had been raised by cardiologists and other researchers at a conference I was presenting at about the hypertensive effect during IRT. Research indicated that there had been no published research conducted into the hypertensive responses during IRT, so I addressed this gap in the literature. <br/> To determine suitability of blood pressure measuring devices utilized in research, I conducted a comparison of the commonly used devices. Reviewer responses from the journal article in Chapter 2 over the reliability of the Finometer, and the lack of research validating the Finometer incited addressing this gap in the literature. <br/> <b>Results</b> Our meta-analysis indicated reductions in systolic blood pressure (SBP) of -5.2mmHg, p<0.01. Similar results were seen at 30% maximum voluntary contraction (MVC) in the first and second studies with reductions of SBP -7mmHg, p=0.04 (8wks) and -7mmHg, p=0.02 (12wks). Diastolic blood pressure (DBP) showed significant reductions in the meta-analysis of -3.91mmHg, p<0.01. Our 8 and 12 week studies saw similar reductions of DBP at 30% MVC -4mmHg, p=0.04 and -5mmHg, p<0.01, respectively. As expected, RPP peak values during exercise were significantly higher than baseline in all IRT intensities assessed, all p≤0.01. <br/> Comparison of blood pressure measurement devices indicated no difference between sphygmomanometer and beat-to-beat SBP (0.23mmHg, p=0.87); however, DBP had a difference of 4.82 mmHg, p<0.01. Ambulatory blood pressure was higher than both sphygmomanometer and beatto- beat measurements for both SBP and DBP with p<0.001 for all measures. <br/> <b>Conclusion</b> There is a positive linear relationship between blood pressure and IRT intensity, this research indicates that cardiovascular responses during IRT are within safe limits. Isometric resistance training is effective at lowering systolic and diastolic blood pressure, and utilization of a 5% MVC group is suitable as a working control.