## 4 Discussion  
The present study evaluated differences in muscle co-contraction and peak EMG activity between novice and advanced Taekwondo athletes during consecutive roundhouse (_bandal chaguu_) kicks. It also aimed to explore the influence of body composition and experience level on these parameters. The results confirm the first hypothesis proposed, indicating significant differences in co-contraction indices between novice and advanced Taekwondo athletes, with effect sizes ranging from moderate to large, particularly in the BF-RF, VM-BF, and SO-TA muscle pairs. These findings suggest that the advanced group \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Muscle** & **Parameter** & **Estimate** & **Std. Error** & **\(p\)-Value** & \begin{tabular}{c} **95\% CI** \\ **Lower** \\ \end{tabular} & \begin{tabular}{c} **95\% CI** \\ **Upper** \\ \end{tabular} & \
\begin{tabular}{c} **R\({}_{\text{m}}\)\({}^{2}\)** \\ \end{tabular} &
\begin{tabular}{c} **R\({}_{\text{m}}\)\({}^{2}\)** \\ \end{tabular} \\ \hline BF & Intercept & 57.99 & 35.52 & 0.103 & \(-\)11.63 & 127.61 & 0.116 & 0.558 \\  & PCA component & 10.21 & 1.68 & \(<\)0.001 * & 6.91 & 13.50 & & \\  & Experience level & 7.79 & 4.67 & 0.095 & \(-\)1.36 & 16.94 & & \\  & Kick number & 2.08 & 0.52 & \(<\)0.001 * & 1.05 & 3.11 & & \\ \hline ST & Intercept & 71.00 & 23.63 & 0.003 * & 24.70 & 117.31 & 0.008 & 0.504 \\  & PCA component & 0.78 & 1.12 & 0.487 & \(-\)1.42 & 2.97 & & \\  & Experience level & 2.17 & 3.10 & 0.484 & \(-\)3.91 & 8.26 & & \\  & Kick number & 0.54 & 0.35 & 0.123 & \(-\)0.15 & 1.22 & & \\ \hline RF & Intercept & 80.38 & 34.47 & 0.020 * & 12.83 & 147.94 & 0.074 & 0.537 \\  & PCA component & 8.14 & 1.63 & \(<\)0.001 * & 4.94 & 11.34 & & \\  & Experience level & \(-\)21.36 & 4.53 & \(<\)0.001 * & \(-\)30.24 & \(-\)12.49 & & \\  & Kick number & 0.24 & 0.51 & 0.639 & \(-\)0.76 & 1.24 & & \\ \hline VM & Intercept & 86.35 & 32.31 & 0.008 * & 23.03 & 149.67 & 0.030 & 0.515 \\  & PCA component & 1.75 & 1.53 & 0.252 & \(-\)1.25 & 4.75 & & \\  & Experience level & \(-\)15.81 & 4.25 & \(<\)0.001 * & \(-\)24.13 & \(-\)7.49 & & \\  & Kick number & 0.40 & 0.48 & 0.406 & \(-\)0.54 & 1.33 & & \\ \hline VL & Intercept & 73.29 & 45.93 & 0.111 & \(-\)16.73 & 163.31 & 0.022 & 0.511 \\  & PCA component & 5.63 & 2.18 & 0.010 * & 1.36 & 9.89 & & \\  & Experience level & \(-\)14.04 & 6.04 & 0.020 * & \(-\)25.87 & 2.21 & & \\  & Kick number & 0.68 & 0.68 & 0.315 & \(-\)0.65 & 2.01 & & \\ \hline LG & Intercept & 75.90 & 35.74 & 0.034 * & 5.85 & 145.95 & 0.008 & 0.504 \\  & PCA component & \(-\)0.28 & 1.69 & 0.870 & \(-\)3.60 & 3.04 & & \\  & Experience level & \(-\)5.14 & 4.70 & 0.274 & \(-\)14.34 & 4.07 & & \\  & Kick number & 0.87 & 0.53 & 0.101 & \(-\)0.17 & 1.90 & & \\ \hline SO & Intercept & 96.69 & 46.18 & 0.036 * & 6.19 & 187.19 & 0.032 & 0.516 \\  & PCA component & 8.18 & 2.19 & \(<\)0.001 * & 3.89 & 12.47 & & \\  & Experience level & \(-\)4.18 & 6.07 & 0.491 & \(-\)16.07 & 7.72 & & \\  & Kick number & 0.92 & 0.68 & 0.176 & \(-\)0.41 & 2.26 & & \\ \hline TA & Intercept & 83.04 & 30.32 & 0.006 * & 23.61 & 142.46 & 0.026 & 0.513 \\  & PCA component & 3.35 & 1.44 & 0.020 * & 0.54 & 6.17 & & \\  & Experience level & \(-\)4.03 & 3.98 & 0.312 & \(-\)11.84 & 3.78 & & \\  & Kick number & \(-\)1.19 & 0.45 & 0.008 * & \(-\)2.07 & \(-\)0.31 & & \\ \hline \hline \end{tabular}  
* BF: _biceps femoris_; LG: _lateral gastrocnemius_; PCA: principal component analysis of adipose mass and muscle mass; RF: _retus femoris_; SO: _solens_; ST: _sentitendinsus_; TA: _tibuils anterior_; VL: _usstus Internis_; VM: _usstus medialis_; *: statistically significant differences.  
\end{table} 
Table 2: Mixed-effects model. exhibited higher co-contraction levels, which may serve as a strategy to enhance joint stabilization and improve precision during consecutive roundhouse (_handal chagui_) kicks. These findings aligned with [PERSON] et al.