The Dose Response Effect of Isometric Handgrip Training Frequency on Blood Pressure and Vascular Health in People With Hypertension: A Randomised Controlled Trial

Hypertension is the most important cause of cardiovascular disease (CVD), stroke, and premature death (WHO, 2021). It is estimated by The World Health Organisation in 2021 that 1.4 billion individuals across the globe have high blood pressure, with only 14% of people actively managing these elevated levels. Simple and effective lifestyle strategies are required to help people improve their blood pressure and/or attenuate increases in blood pressure with ageing. Physical activity is one possible strategy: in previous research, several different types of physical activity have been shown to have beneficial effects on blood pressure (Blackwell et al., 2017). However, many individuals do not adhere to currently recommended levels of physical activity (150 mins of moderate intensity physical activity per week), due to a combination of the required time commitment, lack of motivation, and the associated levels of effort, exertion, and physical discomfort (Korkiakangas et al 2009). Thus, there is a need to identify alternative exercise interventions which will overcome these barriers but remain effective at improving blood pressure (Herrod, Lund, & Phillips, 2021, Toohey et al, 2018).

Low intensity isometric hand grip exercise training (IET) has been shown to result in large decreases in resting blood pressure in younger and older age groups, in both men and women, and in individuals with normal as well as elevated baseline blood pressure (Badrov et al, 2013; Bentley et al., 2018; Millar et al., 2014). In this research, IET has almost universally involved performing 4 x 2 IET holds at 30% of maximal voluntary contraction, 3 times a week, over a 4-8-week intervention (Millar et al, 2014). There are very few studies that have investigated the effect of changing different protocol parameters on changes in blood pressure and vascular health, and the minimal effective dose of IET is unknown. Defining the minimal effective dose of different types of exercise may help overcome key barriers to exercise by lowering the required time commitment, reducing perceived effort/exertion, and promoting more positive affective responses. One important modifiable parameter is training frequency and it is unknown whether reducing the frequency of IET will reduce the efficacy for improving blood pressure.

Therefore, the primary objective of this study is to determine if reducing the frequency of isometric handgrip training from four times a week to two times a week will affect the improvements in resting blood pressure and vascular health in people with hypertension. A secondary objective is to investigate the acute affective and perceptual responses to sessions of IET and the effect of training on these acute affective/perceptual responses.