Isometric Handgrip Training Frequency and Blood Pressure in People With Hypertension

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.

Inclusion Criteria:

• Aged between 18 and 65 years.
• Scoring low or moderate on the international physical activity questionnaire (IPAQ).
• Previous diagnosis of high blood pressure and/or a resting systolic blood pressure ≥130 but <180 mmHg (self-reported and confirmed during screening/baseline assessment).
• Currently taking no anti-hypertensive medicine or taking anti-hypertensive medicine with no treatment change within the last 4 months prior to enrollment.
• Stable dietary and physical activity patterns (including dietary supplementation) over the last 4 months

Exclusion Criteria:

• Aged <18 or >65 years
• Resting blood pressure ≥180/110 mmHg or resting heart rate >100 bpm during baseline as-sessment
• Manifest cardiovascular disease including cerebrovascular disease, heart failure, chronic kidney disease, peripheral vascular disease, or advanced retinopathy (fundus hypertonicus grades III-IV) based on a self-report health history questionnaire.
• Type 1 diabetes
• History of other chronic disease including malignancy, neurological conditions (e.g. multiple sclerosis) or respiratory conditions (e.g. COPD).
• Contraindications to exercise based on answers to the physical activity readiness questionnaire.
• Physical limitations preventing handgrip exercise (e.g. arthritis or other musculoskeletal disorder)
• Scoring "high" on the international physical activity questionnaire
• Taking more than 2 anti-hypertensive drugs or a change in treatment strategy in the previous 4 months.
• Currently taking nitrate medication (as it is commonly prescribed for angina) or on hormone replacement therapy
• Significant self-reported change in lifestyle patterns in the prior 4 months (e.g. currently on a planned diet for weight loss).