The use of the CR-10 scale to allow self-regulation of isometric exercise intensity in pre-hypertensive and hypertensive participants

Purpose Isometric exercise (IE) has been shown to lower blood pressure (BP). Using equipment with force output displays, intensity is usually regulated at 30% maximal voluntary contraction (MVC); however, the cost of programmable equipment and their requirement for maximal contractions presents limitations. A simple, cost-effective alternative deserves investigation. The purpose of this study was (1) to explore the relationship between %MVC, change in systolic BP (ΔSBP), and perceived exertion (CR-10) and (2) to assess the validity of self-regulation of intensity during isometric hand-grip exercise. Methods Fourteen pre-hypertensive and hypertensive adults completed eight, 2-min isometric hand-grip exercises at randomised intensities; participants estimated their perceived exertion at 30-s intervals (estimation task). Subsequently, on three separate occasions, participants performed four 2-min contractions at an exertion level that they perceived to be equivalent to CR-10 “Level-6” (production task). Results There were significant linear relationships between the estimated exertion on the CR-10 scale, and ΔSBP ( r = 0.784) and %MVC ( r = 0.845). Level-6 was equivalent to an average ΔSBP of 38 mmHg (95% CI; 44, 32 mmHg) and a relative force of 33% MVC (95% CI; 36.2, 30%). During the production task, %MVC was not significantly different between the estimation task and each production trial. In at least the first two repetitions of each production trial, ΔSBP was significantly lower than that observed in the estimation task. Conclusion These findings show that CR-10 “Level-6” is an appropriate method of self-regulating isometric hand-grip intensity; its use offers an affordable and accessible alternative for isometric exercise prescription aimed at reducing BP.