## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Rt Hip Knee Extensor** & **Lt Hip Knee Extensor** & **Rt Hand Grip** & **Lt Hand Grip** & **Walking Speed** \\ \hline Rt hip knee extensor & - & - & - & - & - \\ Lt hip knee extensor & 0.896 \(\uparrow\) (\(<\)0.001) & - & - & - & - \\ Rt hand grip & 0.325 \(\uparrow\) (\(<\)0.001) & 0.255 (0.084) & - & - & - \\ Lt hand grip & 0.333 \(\uparrow\) (\(<\)0.001) & 0.323 \(\uparrow\) (\(<\)0.001) & 0.913 \(\uparrow\) (\(<\)0.001) & - & - \\ Walking speed & 0.028 (0.850) & 0.079 (0.600) & 0.375 \({}^{*}\) (0.009) & 0.302 \({}^{*}\) (0.039) & - \\ \hline \hline \end{tabular}  
* Correlation is significant at the 0.05 level. \(\dagger\) Correlation is significant at the 0.01 level. Rt, right; Lt, Left.  
\end{table} 
Table 5: Correlation among muscle strength analysis (r, Pearson correlation) (\(n=47\)). it required only one to three STS. Third, it can assess the right and left lower extremity muscle strength individually. There are numerous studies that use force plates to measure muscle strength. In previous studies, two force plates were used to evaluate the weight bearing of the right or left side of the foot, without touching the wall with the hand, and the measured values were peak ground force and the rate of force development [39; 40]. Performing the STS test without wall touch reflects lower extremity muscle strength and balance ability [41]. We believe that it is possible to measure pure muscle strength by performing STS with the hand slightly touching the wall, and it improves safety when performing the movement. The relationship between the GRF during STS and lower extremity strength remains unclear. [PERSON] and [PERSON] reported that in older women, GRF showed a moderate correlation with isometric knee extension muscle strength [42]. [PERSON] et al. revealed that the GRF parameter in STS is related to muscle strength in the knee and ankle [40]. However, this measurement method is not yet practically used as a field test, owing to the requirement of expensive special equipment and the lack of an accurate execution protocol for chair height and time when performing STS [40]. On the other hand, our study has an advantage in that it provides a method for measuring lower extremity muscle strength using GRF with a relatively simple and applicable setting. No significant correlation was observed between the hip and knee strength measured by HHD and GRF AI, considering that the Pearson correlation coefficient was approximately 0.034-0.094. The new method measured closed kinetic chain muscle strength; however, the use of HHD for open kinetic chain muscle strength may explain this result [43; 44]. Therefore, we planned to test closed kinetics strength using the inverse dynamics method [45]. In addition, no significant correlation was observed between the GRF AI and hand grip strength. This could be explained by the different muscles tested. Grip strength measures the strength of the forearm muscles, whereas the GRF AI measures the strength of lower limb muscles. Another explanation is the limitation of the new test--the ceiling effect. GRF AI was distributed at approximately 0.69. If the ceiling effect could be reduced, the correlation between the two tests may be improved. HHD and grip strength showed a high correlation on the right and left sides, respectively, with a Pearson correlation coefficient of 0.896-0.913. This finding was consistent with the correlation between grip strength and muscle strength measured by HHD in previous studies [18; 30]. There was no significant correlation between the new test and walking speed. Because the study was conducted in relatively healthy participants aged \(\geq\)40 years, it was considered that the correlation between walking speed and other muscle strength evaluations was not high, as the minimum strength required for performing tasks is different and reserve capacity exists in healthy individuals [46]. It may be the ceiling effect of this new test for measuring lower extremity muscle strength.