Isometric Resistance Training and Dose-dependent Effects in Pre- and Hypertensive Adults

The World Health Organisation have reported hypertension, a major risk factor for cardiovascular disease (CVD), strokes and coronary heart disease (CHD), to be near epidemic levels globally with over 30% of the world's population, at this time, suffering from hypertension. Over the past twenty years isometric resistance training (IRT) has been established as one of the best forms of nonpharmacological interventions for the prevention and treatment of hypertension and endorsed by the American College of Cardiology / American Heart Association in their most recent guidelines. Thrice weekly IRT programmes undertaken (4 x 2-minute isometric contractions) at 20-30% of an individual's maximum voluntary contraction (MVC) for a period of 4-10 weeks have demonstrated reductions in clinic resting and ambulatory systolic blood pressure (-4 to -10 mmHg), in both normotensive and hypertensive men and women with no reported difference in the magnitude of these reductions between women and men. Whilst isometric training has been shown to produce clinically meaningful reductions in blood pressure, utilising the commonly used protocol (4 x 2-min contractions) three-times a week, one of the main barriers to therapeutic exercise interventions is time to undertake the intervention and despite the observed benefits, adherence and compliance tends to be low. Indeed, regular exercise adherence declines over time, with only 50% of individuals continuing with regular exercise within the first twelve months following the completion of a therapeutic treatment, with a lack of perceived time cited as one of the main barriers. With this in mind, it is important to determine the effects of training dose on the changes in blood pressure seen following IRT. To date there is very little research into the effects of IRT dose on resting blood pressure with only one study purposely investigated the area. Whilst to the authors knowledge no studies have investigated the effects of altered training dose on ambulatory or diurnal blood pressure variations. Although three times a week has become the most commonly applied protocol there is no evidence to confirm that it is the most efficacious. As training dose is an important determinant of adaptations to exercise training, and with a lack of time cited as a perceived barrier to undertaking exercise, there is a need to determine the most efficacious training protocol to elicit clinical reductions in blood pressure, including shorter time saving (once or twice weekly) protocols. Therefore, the study aims are to determine if a reduction in the weekly dose of isometric training, such as a reduction in the number of total contractions and therefore a reduced time commitment (once or twice weekly) would produce a similar hypotensive response to those reported.