## 4 Discussion  
This is the first study on the functional validity of the knee flexor-to-extensor ratios measured by tensiomyography (TMG). We investigated the correlations between conventional and functional isokinetic torque ratios and the ratios of time and amplitude TMG \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{4}{c}{**Functional Isokinetic Torque Ratios**} \\ \hline
**TMG Ratios** & \(\rm\bf{FL_{E}/EXT_{C}}\) **60\({}^{\circ}\)/s** & \(\rm\bf{FL_{E}/EXT_{C}}\) **180\({}^{\circ}\)/s** & \(\rm\bf{FL_{E}/EXT_{C}}\) **240\({}^{\circ}\)/s** \\ \hline H/QF TMG & 0.054 & 0.240 & 0.381 \({}^{*}\) \\ \(\rm T_{\rm{C}PL}/\rm T_{\rm{E}XT}\) & \(-\)0.211 & \(-\)0.348 & \(-\)0.198 \\ \(\rm T_{\rm{B}PF}/\rm T_{\rm{E}XT}\) & \(-\)0.225 & \(-\)0.264 & \(-\)0.216 \\ \(\rm T_{\rm{C}PL}/\rm T_{\rm{E}XT}\) & \(-\)0.175 & \(-\)0.465 \({}^{**}\) & \(-\)0.366 \({}^{*}\) \\ \(\rm T_{\rm{C}PL}/\rm T_{\rm{E}XT}\) & \(-\)0.311 & \(-\)0.468 \({}^{**}\) & \(-\)0.408 \({}^{*}\) \\ \(\rm T_{\rm{S}PL}/\rm T_{\rm{E}XT}\) & \(-\)0.195 & 0.020 & \(-\)0.002 \\ \(\rm T_{\rm{B}PF}/\rm T_{\rm{E}XT}\) & \(-\)0.251 & \(-\)0.038 & \(-\)0.035 \\ \(\rm Dm_{\rm{F}L}/\rm Dm_{\rm{E}XT}\) & \(-\)0.175 & \(-\)0.099 & 0.124 \\ \(\rm Dm_{\rm{B}PF}/\rm Dm_{\rm{E}XT}\) & \(-\)0.142 & \(-\)0.112 & \(-\)0.013 \\ \hline \hline \end{tabular} H/QF TMG—default hammstings-to-quadriceps ratio of knee muscles calculated by the data acquisition and analysis software (TMG-S1, Ljubliana, Slovenia). \({}^{**-}\)–statistically significant correlation at \(p\)\(<\) 0.01; \({}^{**-}\)–statistically significant correlation at \(p\)\(<\) 0.05.  
\end{table} 
Table 6: Values of the correlation coefficients (r) between the functional ratio (\(\rm\rm\rm\rm\rm\rm\rm\rm\)\rm\) (\(\rm\rm\rm\rm\rm\)  
parameters of the same muscle groups. In general, the correlations between the isokinetic torque ratios and the TMG ratios were low and not significant. Nevertheless, some TMG ratios, especially those calculated from the contraction time (Tc), were weakly to moderately correlated with the isokinetic torque ratios. A negative correlation was found between the functional isokinetic torque ratio measured at 180\({}^{\circ}\)/s and 240\({}^{\circ}\)/s and the \(\mathrm{Tc_{FL}}\)/\(\mathrm{Tc_{EXT}}\) and \(\mathrm{Tc_{EF}}\)/\(\mathrm{Tc_{EXT}}\) ratios measured by TMG. In addition, a negative correlation was found between the conventional isokinetic ratio of the knee muscles at 60\({}^{\circ}\)/s and \(\mathrm{Td_{FL}}\)/\(\mathrm{Td_{EXT}}\). In contrast, a positive correlation was found between the functional isokinetic ratio measured at 240\({}^{\circ}\)/s and the default H/QF TMG ratio. However, we found no significant correlations between the ratios calculated from the TMG amplitude of muscle transverse displacement and any of the isokinetic torque ratios. TMG measurements have been shown to be valid and useful for the non-invasive assessment of muscle fibre composition, muscle tone, adaptation of muscle contractility to exercise, the degree of peripheral fatigue, the effects of muscle injury and the speed of its recovery, and the assessment of lateral muscle (a)symmetries [19]. However, the relationship between the TMG parameters and the standard indices of isokinetic dynamometry, i.e., the functional validity of TMG, is still poorly understood. The series of articles by [PERSON] et al. [11; 12; 13] has shown some weak to moderate correlations between the basic parameters of the two measurement methods. Based on these results, we hypothesised that there must also be an important relationship between the isokinetic flexor-to-extensor torque ratios and their counterpart ratios calculated from the TMG parameters. However, the results of our experiment did not confirm these assumptions. As for the conventional (concentric) isokinetic torque ratios, the only statistically significant correlation was found with the \(\mathrm{Td_{FL}}\)/\(\mathrm{Td_{EXT}}\) ratio (r = \(-\)0.397; \(p\) = 0.03).