Concurrent Validity and Reliability of a Handheld Dynamometer in Measuring Isometric Shoulder Rotational Strength

Context: Measuring isometric shoulder rotational strength is clinically important for evaluating motor disability in athletes with shoulder injuries. Recent evidence suggests that handheld dynamometry may provide a low-cost and portable method for the clinical assessment of isometric shoulder strength. Objective: To investigate the concurrent validity and the intrarater and interrater reliability of handheld dynamometry for measuring isometric shoulder rotational strength. Design: Cross-sectional study. Setting: Biomechanics laboratory. Participants: Thirty-nine young, healthy participants. Main Outcome Measures: The peak isometric strength of the internal rotators and external rotators, measured by handheld dynamometry (in newton) and isokinetic dynamometry (in newton meter). Interventions: Maximal isometric shoulder rotational strength was measured as participants lay supine with 90 degrees shoulder abduction, neutral rotation, 90 degrees elbow flexion, and forearm pronation. Measurements were performed independently by 2 different physiotherapists and in 3 different sessions to evaluate interrater and intrarater reliability. The data obtained by handheld dynamometry were compared with those obtained by isokinetic testing to evaluate concurrent validity. Results: The intraclass correlation coefficients for interrater reliability in measuring maximum isometric shoulder external and internal rotation strength were .914 (95% confidence interval [CI], .842-.954) and .842 (95% CI, .720-.914), respectively. The intrarater reliability values of the method for measuring maximal shoulder external and internal rotation strength were 0.865 (95% CI, 0.757-0.927) and 0.901 (95% CI, 0.820-0.947), respectively. The Pearson correlation coefficients between the handheld and isokinetic dynamometer measurements were.792 (95% CI, .575-.905) for external rotation strength and .664 (95% CI, .419-.839) for internal rotation strength. Conclusions: The handheld dynamometer showed good to excellent reliability and moderate to good validity in measuring maximum isometric shoulder rotational strength. Therefore, handheld dynamometry could be acceptable for health and sports professionals in field situations to evaluate maximum isometric shoulder rotational strength.