Twenty weeks of isometric handgrip home training to lower blood pressure in hypertensive older adults: a study protocol for a randomized controlled trial

Hypertension (HT) is a major public health concern worldwide with an upward trend [1]. HT increases the risk of cardiovascular diseases (e.g., coronary artery disease, stroke, and heart failure) and overall mortality [2, 3]. Both European and US treatment guidelines for primary and secondary prevention of HT recommend non-pharmacological lifestyle modifications, such as increased levels of physical activity, as the first line of anti-hypertensive therapy [4, 5]. In addition, there is class I, level B evidence that 150 min of weekly physical activity offers an alternative that may be used to complement anti-hypertensive medication, although optimal exercise training regime remains unclear [6]. A systematic review from 2013 highlighted the potential of isometric handgrip (IHG) training regimens in reducing systolic blood pressure (SBP) [7]. The meta-analysis from the review showed that IHG training was superior to endurance training and dynamic resistance training in reducing SBP (by − 10.9, − 3.5, and − 1.8 mmHg, respectively) [7]. Another systematic review published in 2014 on IHG training, including isometric leg extension training, reported a more modest mean difference of − 6.77 mmHg in SBP [8]. Lately in 2016, yet another systematic review was published on isometric training (both handgrip and leg extension) and showed an overall reduction in SBP of − 5.2 mmHg [9]. This review, however, was heterogenetic in nature with several outlying studies, which may have undermined the effect of isometric training on blood pressure levels. In addition, some of the studies included in the most recent review were performed on normotensive populations and may have contributed to a reduced effect compared to the systematic review from 2013. Overall, most isometric exercise training studies have followed somewhat the same exercise protocol with an intensity of 30% of maximum voluntary contraction (MVC) in intervals of 2 min per hand/foot (a total of 8 min per hand/foot per day). In addition, the training has been three times per week for an average of 7.5 weeks in duration with the longest reported study being 10 weeks [9]. Most of the studies have been conducted at a hospital, university, or healthcare clinic burdening the participant by having to travel to the study site for assessment and training. Finally, many of the previous studies on IHG training have been relatively small in size (average 28 participants) [9].

Recently, we have shown that handgrip [10] and lower extremity strength [11] can be measured precisely using a standard Nintendo Wii Board (Wii) with an on-screen visual feedback of the force exerted over time (force/velocity curve). As a continuation of this work, we have further developed a novel method that monitors handgrip muscle control and is suitable for IHG home training. Given the development and low-cost nature of the Wii, we are now able to perform home-based IHG training. For the above reasons we intend to conduct a IHG training study, which will be twice as long (20 weeks) as the longest previous study (10 weeks) to explore the effects on specific measures of blood pressure and other relevant outcomes. Our primary aim is to explore the effects of 20 weeks’ IHG home training facilitated by a Wii in hypertensive older adults (50 + years of age) in lowering SBP. Secondary aims are to explore if/when a leveling-off effect on SBP will occur during the 20-week intervention period in the training group and to explore adherence and potential harms related to the IHG home training. The study will compare IHG home training with a control group in a randomized, assessor-blinded design. Thus, we hypothesize (1) that 20 weeks of IHG home training will significantly reduce SBP in hypertensive older men and women compared to usual care, (2) that a leveling-off effect on SBP will occur during the 20 weeks of IHG training, and (3) that a minimum of 50% of participants will complete at least 50% of their training sessions (30 sessions).