Psychometric properties of a standardized protocol of muscle strength assessment by hand-held dynamometry in healthy adults: a reliability study

BACKGROUND: Maximal isometric muscle strength (MIMS) assessment is a key component of physiotherapists’ work. Hand-held dynamometry (HHD) is a simple and quick method to obtain quantified MIMS values that have been shown to be valid, reliable, and more responsive than manual muscle testing. However, the lack of MIMS reference values for several muscle groups in healthy adults with well-known psychometric properties limits the use and the interpretation of these measures obtained with HHD in clinic. OBJECTIVE: To determine the intra- and inter-rater reliability, standard error of measurement (SEM) and minimal detectable change (MDC) of MIMS torque values obtained with HHD. METHODS: Intra and Inter-rater Reliability Study. The MIMS torque of 17 muscle groups was assessed by two independent raters at three different times in 30 healthy adults using a standardized HHD protocol using the MEDup™ (Atlas Medic, Québec, Canada). Participants were excluded if they presented any of the following criteria: 1) participation in sport at a competitive level; 2) degenerative or neuromusculoskeletal disease that could affect torque measurements; 3) traumatic experience or disease in the previous years that could affect their muscle function; and 4) use of medication that could impact muscle strength (e.g., muscle relaxants, analgesics, opioids) at the time of the evaluation. Intra- and inter-rater reliability were determined using two-way mixed (intra) and random effects (inter) absolute agreement intraclass correlation coefficients (ICC: 95% confidence interval) models. SEM and MDC were calculated from these data. RESULTS: Intra- and inter-rater reliability were excellent with ICC (95% confidence interval) varying from 0.90 to 0.99 (0.85–0.99) and 0.89 to 0.99 (0.55–0.995), respectively. Absolute SEM and MDC for intra-rater reliability ranged from 0.14 to 3.20 Nm and 0.38 to 8.87 Nm, respectively, and from 0.17 to 5.80 Nm and 0.47 to 16.06 Nm for inter-rater reliability, respectively. CONCLUSIONS: The excellent reliability obtained in this study suggest that the use of such a standardized HHD protocol is a method of choice for MIMS torque measurements in both clinical and research settings. And the identification of the now known metrological qualities of such a protocol should encourage and promote the optimal use of manual dynamometry. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12891-023-06400-2.