Validity and reliability of the ‘Isometric Exercise Scale’ (IES) for measuring ratings of perceived exertion during continuous isometric exercise

Purpose: Isometric exercise (IE) interventions have been shown to be effective at reducing resting arterial blood pressure (BP). IE intensity is generally determined using force, electromyography (EMG), heart rate (HR), or knee joint angle. However, ratings of perceived exertion (RPE) may provide a more accessible means of determining exercise intensity. Therefore, the aim of this study was to assess the validity of a specific Isometric Exercise Scale (IES) during a continuous incremental isometric wall squat test.

Methods: Twenty-nine male participants completed 4 incremental IE tests. Each test consisted of 5 isometric wall squat intensities, determined by knee joint angles from 135° to 95°, each held for up to 2 minutes. The tests were continuous until volitional fatigue or completion of the 5 work stages. Throughout the exercise protocol, RPE (IES and Borg’s CR-10), HR and blood pressure were recorded.

Results: The IES produced a strong positive linear relationship with the CR-10 (r = 0.967) . Additionally, strong positive relationships between the IES and wall squat duration (r = 0.849), HR (r = 0.819) and BP (r = 0.841) were seen. Intra-class correlation coefficients and coefficients of variations for the IES ranged from r = 0.81 to 0.91 and 4.5% to 54% respectively, with greater reliability seen at the higher workloads.

Conclusions: The IES is a valid and reliable measure of RPE, exercise intensity, and it accurately represents the changes in physiological measures of exertion during IE; as such, the IES can be used as a useful additional measure of exercise intensity during IET interventions.