## 4 Discussion  
The objective of this study was to examine the reliability and validity of the Activ5 dynamometer for assessing grip strength in a population of adults. The results of this study reveal that both the Jamar dynamometer and the Activ5 are reliable in assessing grip strength. Manual dynamometry showed good to excellent reliability in assessing the isometric muscle strength of the arm musculature in a healthy population. Our findings are consistent with scientific evidence reporting that the Jamar dynamometer has high levels of reliability (ICC) [26,31]. Thus, ICC values and the 95% confidence interval for both devices were above 0.91, indicating excellent intratest reliability. To the best of our knowledge, this is the first study evaluating the reliability and validity of the Activ5 dynamometer by comparing it with the gold-standard instrument. Figure 5: Bland–Altman plot of the differences for the left hand. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Instrument** & **Condition** & **ICC** & **Lower Limit** & **Upper Limit** & **Cronbach’s Alpha** \\ \hline \multirow{2}{*}{Jamar dynamometer} & Right & 0.955 & 0.936 & 0.968 & 0.957 \\ \cline{2-6}  & Left & 0.959 & 0.938 & 0.973 & 0.965 \\ \hline \multirow{2}{*}{Activ5} & Right & 0.930 & 0.895 & 0.953 & 0.938 \\ \cline{2-6}  & Left & 0.913 & 0.875 & 0.940 & 0.920 \\ \hline \end{tabular} Note.: ICC: intraclass correlation coefficient.  
\end{table} 
Table 3: Intraclass correlation coefficient (ICC) for Jamar dynamometer and Activ5 under two conditions. Similarly, the present study, to evaluate the reliability of the Activ5 instrument in grip strength assessment, considered the sample size references for determining instrument reliability elaborated by the Consensus for the Selection of Health Measurement Instruments (COSMIN) [45]. There, it is reported that to determine whether the sample size included in the analysis is adequate, the sample size must be (\(\geq\)100) to achieve an excellent category. The present study considered the evaluation of 106 individuals. Regarding reliability, highly positive correlations were found through [PERSON]'s test, revealing that if the assessment with one instrument increased, so did the other instrument [32; 46]. These findings correspond to those reported in other studies using other instruments. Following the findings reported by [PERSON] et al. [47], the use of objective measures for determining manual muscle testing (MMT) is a line of research that needs to be developed, as is the establishment of other possible issues, beyond muscle weakness, that are commonly determined by dynamometry usage. This is why the validation of a dynamometer like the Activ5 could help understand this issue: this instrument and its application were designed to perform real-time monitoring and evaluation of different postures in different populations. Another important aspect of the validation process of other portable instruments lies in how weight generates ease or difficulty in maneuvering the instrument, which can cause different efforts due to the position of the joints when generating force [48; 49]. This is in response to the variety of portable dynamometers available, where their different grips require different validation and reliability studies to be performed [48]. These issues should be solved in the form of longitudinal studies, which can be conducted using instruments that allow for feedback on the produced force, as Activ5 does. The Activ5 dynamometer allows for the instantaneous recording of grip strength assessment through projection on a mobile phone screen, which can help the individual to regulate his or her muscle control and generate rapid feedback. Given the above, and comparing the results obtained, it can be assumed that the difference in force measurement between both dynamometers is small and that the upper-lower limits are narrow, which can lead to the belief that the Activ5 dynamometer is optimal for use in grip strength assessment in healthy populations or individual monitoring.