Validity, reliability, and diagnostic accuracy of the InGrip digital dynamometer compared with the Jamar hydraulic model in older adults

INTRODUCTION: Handgrip strength is essential for diagnosing sarcopenia and assessing muscle function in older adults. The Jamar hydraulic dynamometer, backed by strong clinical and epidemiological data, is widely used; however, weight and calibration requirements may limit use. Digital models such as InGrip offer stable calibration and ergonomic design. This study aimed to validate accuracy, reliability, and diagnostic performance of InGrip versus the Jamar. METHODS: A cross-sectional, randomized, single-center study of 415 community-dwelling older adults (mean age: 75.3 ± 6.5 years). Handgrip strength was measured with both devices per the Southampton protocol. Correlation and agreement (Bland-Altman, ICC) between InGrip and the reference dynamometer (Jamar) were analyzed, and diagnostic capacity via ROC curves, estimating sensitivity, specificity, and predictive values for low handgrip strength per EWGSOP2 criteria. RESULTS: The InGrip dynamometer showed strong correlation with the Jamar dynamometer (r = 0.95) and excellent agreement (ICC = 0.94), intra-observer (ICC = 0.96), and inter-observer (ICC = 0.96), with a mean bias of - 0.37 kg and limits of agreement from - 4.45 to 3.72 kg. Its diagnostic capacity was high (AUC women = 0.968; AUC men = 0.982). Optimal cutoffs were ≤ 18 kg for women (sensitivity = 92.6%, specificity = 90.5%) and ≤ 27.5 kg for men (sensitivity = 96%, specificity = 93%). CONCLUSION: The InGrip digital dynamometer showed excellent validity, reliability, and diagnostic accuracy compared to the Jamar in community-dwelling older adults, with sex-specific cutoffs aligned with EWGSOP2 criteria, supporting its use as a practical alternative for strength assessment in research and clinical practice. TRIAL REGISTRATION: ClinicalTrials.gov NCT06623019.