Reliability of the Five-Position Bell Curve Test Comparing the BTE Tech PrimusRS to the Jamar Dynamometer

Purpose: This study examines the test-retest reliability and concurrent validity of the Five-Position Bell Curve Test using the BTE PrimusRS, comparing its performance to the Jamar dynamometer. Given the critical role of grip strength in occupational health and rehabilitation, ensuring the validity of assessment tools is essential for clinical decision-making and functional evaluations. Methods: A total of 61 adults with no upper extremity pathology (27 males, 34 females) completed two identical testing sessions involving the Five-Position Bell Curve Test on both devices. Testing followed ASHT grip strength protocols, with randomized instrument order and standardized posture, grip technique, and rest periods. Intraclass correlation coefficients (ICC) and paired t-tests assessed measurement consistency across all five fret positions for both hands. Results: ICC values were near-identical (≥0.999 - 1.000) across all fret positions, indicating excellent test-retest reliability and concurrent validity between instruments. Only one statistically significant difference was observed (Fret 1, Left Hand: t(33) = 2.073, p = 0.046, d = 0.361), suggesting a minor measurement deviation. Overall, grip strength measurements between BTE PrimusRS and Jamar dynamometer were highly comparable, supporting their interchangeability for clinical assessments. Conclusion: The BTE PrimusRS demonstrates excellent test-retest reliability and concurrent validity in performing the Five- Position Bell Curve Test, aligning with the measurement validity of the Jamar dynamometer. While results confirm its clinical applicability, future research should explore its reliability in populations with upper extremity injuries and neurological impairments.