Reliability and validity of a load cell device for hand grip strength assessment Confiabilidade e validade de um dispositivo de célula de carga para avaliação da força de preensão palmar Fiabilidad y validez de un dispositivo de célula de carga para evaluar la fuerza de prensión palmar

The grip strength is a complex measure influenced by factors such as gender, age, motivation, muscle training, handedness, height, weight, socioeconomic variables, and participation in specific sports or professions. It can be measured by dynamometers or by tension meters such as load cells (strain gauges). Reliability and validity are important psychometric properties, which analyze consistency and applicability of an instruments' measurement. Thus, the aim of this study was to evaluate the test-retest reliability and construct validity of a load cell device in isometric grip force measurements using a sample of asymptomatic subjects and patients with wrist and hand dysfunctions. Standardized methods of the upper limb positioning and randomization of the sample order were used. Statistical analysis of reliability was conducted by the ICC (Intraclass Correlation Coefficient) and the construct validity by Pearson correlation coefficient (r), with p<0.05, 95% CI, using SPSS version 20 ® . The sample consisted of 24 healthy volunteers with an average age of 22.25 years old, all college students, and 21 volunteers with upper extremity and hand disorders, from both genders. The test-retest reliability for the asymptomatic group was ICC 0.90 (0.78-0.95) and for the group of patients was 0.94 (0.87-0.97), both considered excellent. The Bland and Altman graphics showed that although the reliability has displayed excellent levels and low standard error values of measurement, some discrepant data were found. Pearson correlation coefficients were high, both 378 for the asymptomatic group (r=0.85), and for the patients group (r=0.83). Conclusion: based on these findings, it is suggested that this load cell is a reliable and valid device for isometric grip strength measurement and its use is suitable for future clinical trials and practice.