## 3 Results  
The sample consisted of 62 subjects of 20.42 \(\pm\) 4.97 years, with most of the participants being women (59.7%) with right dominance (88.7%) (Table 1). \begin{table}
\begin{tabular}{l c c} \hline N & & 62 \\ \hline Gender, \(n\) (\%) & Female & 37 (59.7) \\ \hline  & Male & 25 (40.3) \\ \hline Age & & 20.42 \(\pm\) 4.97 \\ \hline Height (cm) & & 169.81 \(\pm\) 8.74 \\ \hline Weight (kg) & & 64.01 \(\pm\) 9.64 \\ \hline Lower limb dominance, \(n\) (\%) & Left & 7 (11.3) \\ \hline  & Right & 55 (88.7) \\ \hline Dominant lower limb length (cm) & & 86.97 \(\pm\) 4.84 \\ \hline Rectus femoris length (cm) & & 33.94 \(\pm\) 2.99 \\ \hline Quadriceps tendon length (cm) & & 7.14 \(\pm\) 1.77 \\ \hline Distance between spines (cm) & & 4.38 \(\pm\) 3.32 \\ \hline Proximal third perimeter (cm) & & 61.04 \(\pm\) 5.45 \\ \hline Middle third perimeter (cm) & & 55.79 \(\pm\) 5.00 \\ \hline \end{tabular}
\end{table} 
Table 1: Clinical and demographic characteristics of the participants. Significant differences are shown in the variable average velocity contraction (cm/sg) (\(Z\) = 9.661, \(p\) < 0.001) with a velocity difference of \(-\)2.1 (\(-\)2.742, \(-\)1.588) cm/s greater in the VIM and a large and significant effect size, and in the variable average velocity relaxation (cm/sg) (\(Z\) = 9.548, \(p\) < 0.001) with a velocity difference of \(-\)1.122 (\(-\)1.392, \(-\)0.885) cm/s greater in the VIM and with an effect size that is also large and significant (Table 2). In the GEE model, both the QIC and the ANOVA test indicate that the model with the variables' contraction ratio and average velocity relaxation is the most appropriate (Supplementary Materials Table S1). It verifies that the exchangeable correlation structure is the one that presents the lowest QIC and the smallest difference between the naive and sandwich estimators (Supplementary Materials Table S2). The odds ratio of the final model indicates that, significantly, for each point increase in the contraction ratio the probability that the target muscle is the RF decreases 0.9 times (0.827, 0.98) whereas, for each point of increase in the average velocity relaxation the probability that the target muscle is the rectus femoris increases 1.023 times (1.016, 1.03), that is, the RF is associated with increments in the average velocity relaxation while the VIM is associated with increments in the contraction ratio (Table 3). \begin{table}
\begin{tabular}{l l l} \hline Distal third perimeter (cm) & 47.13 \(\pm\) 4.28 \\ \hline Rectus femoris thickness at rest (cm) & 2.11 \(\pm\) 0.44 \\ \hline Rectus femoris thickness contraction (cm) & 2.72 \(\pm\) 0.52 \\ \hline Rectus femoris contraction ratio (\%) & 0.30 \(\pm\) 0.13 \\ \hline Vastus intermedius thickness at rest (cm) & 1.69 \(\pm\) 0.40 \\ \hline Vastus intermedius contraction thickness (cm) & 2.11 \(\pm\) 0.38 \\ \hline Vastus intermedius contraction ratio (\%) & 0.27 \(\pm\) 0.17 \\ \hline Rectus femoris average velocity contraction (cm/sg) & 4.42 \(\pm\) 2.51 \\ \hline Rectus femoris average relaxation velocity (cm/sg) & 2.39 \(\pm\) 0.77 \\ \hline Vastus intermedius average contraction velocity (cm/sg) & 7.44 \(\pm\) 7.07 \\ \hline Vastus intermedius average relaxation velocity (cm/sg) & 3.58 \(\pm\) 1.25 \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
The ROC curve shows a significant AUC of 82.544% 95%CI (75.246-89.843%), which indicates a high discriminatory capacity of the model (Figure 3). Significant correlations (_p_ < 0.05) occur in the RF mean thickness at rest vs. RF length, VIM mean contraction thickness vs. distal third perimeter, VIM mean contraction thickness vs. dominant lower limb length, VIM mean contraction thickness vs. middle third perimeter, VIM mean contraction thickness vs. RF length, VIM mean thickness at rest vs. distal third perimeter, VIM mean thickness at rest vs. dominant lower limb length, VIM mean thickness at rest vs. middle third perimeter, VIM mean thickness at rest vs. proximal third perimeter and VIM mean thickness at rest vs. RF length.