Validity and Reliability of Isometric Muscle Strength using the Powrlink Portable Device

Background: A muscle strength testing device that is convenient, practical, reliable, and valid is essential in clinical and field settings. Objective: Therefore, the purpose of this study was to determine the validity and reliability of measuring isometric muscle strength with the Powrlink handheld dynamometer compared to an established force dynamometer. Method: Sixty-one university students (40 males and 21 females) completed two standardized testing sessions seven days apart. Each session consisted of a familiarization period followed by three peak isometric muscle strength tests. Intraclass correlation (ICC, model: two-way mixture with absolute agreement), standard error of measurement (SEM), minimum detectable change (MDC), and 95% limits of agreement (LOA) for intra- and inter-rater reliability were determined. Results: Test-retest reliability (ICC > 0.91) and intertrial reliability (ICC > 0.99) were excellent. No significant differences were observed in peak and mean knee forces and torques between the test and retest, indicating high test-retest reliability. Conclusion: The Powrlink device is portable, convenient, responsive, and cost-effective, has excellent test-retest reliability, and can be used to measure maximal isometric force in the clinic and in the field.