## 3 Results
### Joint Kinematics  
The analysis of joint kinematics revealed significant effects of difficulty on various kinematic variables at both the start and end of the takeoff phase. At the start of the takeoff \begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline  & **Bs 720** & **Bs 1080** & **Bs 1440** & **Bs 1800** & **F\({}_{\text{3,36}}\)** & \(p\)-Value** & \(\eta_{\text{p}}^{2}\) \\ \hline Takeoff time (s) & 0.41 \(\pm\) 0.03 & 0.51 \(\pm\) 0.05 a & 0.52 \(\pm\) 0.05 a & 0.59 \(\pm\) 0.05 abc & 22.88 & \textless{}0.001 & 0.73 \\ Flight time (s) & 2.33 \(\pm\) 0.1 & 2.47 \(\pm\) 0.06 a & 2.58 \(\pm\) 0.08 ab & 2.64 \(\pm\) 0.04 ab & 58.27 & \textless{}0.001 & 0.87 \\ Flight height (m) & 3.26 \(\pm\) 0.27 & 3.68 \(\pm\) 0.19 & 4.03 \(\pm\) 0.48 ab & 3.98 \(\pm\) 0.46 ab & 28.52 & \textless{}0.001 & 0.77 \\ Departure & & & & & & & \\ combined velocity & 14.7 \(\pm\) 0.5 & 15.3 \(\pm\) 0.3 & 15.9 \(\pm\) 0.3 ab & 16.4 \(\pm\) 0.5 abc & 41.07 & \textless{}0.001 & 0.83 \\ (m/s) & & & & & & & \\ Departure vertical & & & & & & & \\ velocity (m/s) & & & & & & & \\ departure angle (\({}^{\circ}\)) & 29.6 \(\pm\) 3.4 & 35 \(\pm\) 1.5 a & 34.8 \(\pm\) 1.2 a & 33.9 \(\pm\) 1.9 a & 9.32 & \textless{}0.001 & 0.53 \\ \hline \hline \end{tabular}  
* significant difference from Bs 720; b significant difference from Bs 1080; c significant difference from Bs 1440.  
\end{table} 
Table 1: Performance metrics of SBA at different difficulty levels during takeoff and flight phases. (Figure 2), significant changes were observed in the upper trunk twist angle (F\({}_{3,36}\) = 3.6, \(p\) = 0.029, \(\eta_{\rm p}^{2}\) = 0.3), shoulder horizontal abduction angle (F\({}_{3,36}\) = 8.2, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.5), hip flexion angle (F\({}_{3,36}\) = 7, \(p\) = 0.001, \(\eta_{\rm p}^{2}\) = 0.46), knee flexion angle (F\({}_{3,36}\) = 23.7, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.74), and elbow flexion angle (F\({}_{3,36}\) = 8.2, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.5). Specifically, the upper trunk twist angle and shoulder horizontal abduction angle increased significantly with difficulty, showing total gains of 121.1% and 98.6%, respectively. In contrast, the hip flexion angle, knee flexion angle, and elbow flexion angle decreased significantly, with total reductions of 61%, 37.3%, and 74.7%, respectively. These parameters all showed large effect sizes, indicating that changes in joint kinematics due to increased difficulty are not only statistically significant but also practically important for performance adaptation. At the end of the takeoff (Figure 3), significant effects were noted for the hip extension angle (F\({}_{3,36}\) = 24.3, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.74) and knee flexion angle (F\({}_{3,36}\) = 23.7, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.74), with the hip extension angle showing a remarkable total gain of 528%. The knee flexion angle also increased significantly, with a total gain of 55.4%. Both parameters demonstrated large effect sizes, further supporting the practical significance of these kinematic adaptations in response to increased difficulty. The range of motion (ROM, Figure 4) for several kinematic variables was significantly affected by difficulty, including the upper trunk twist angle (F\({}_{3,36}\) = 11.4, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.58), the shoulder horizontal angle (F\({}_{3,36}\) = 13.6, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.62), the hip sagittal angle (F\({}_{3,36}\) = 20, \(p\) < 0.001, \(\eta_{\rm p}^{2}\) = 0.71), the knee angle (F\({}_{3,36}\) = 6.4, \(p\) = 0.002, \(\eta_{\rm p}^{2}\) = 0.43), and the elbow angle (F\({}_{3,36}\) = 5.7, \(p\) = 0.004, \(\eta_{\rm p}^{2}\) = 0.4). The upper trunk twist angle exhibited a total gain of 130.9%, while the shoulder horizontal angle showed a total gain of 98.5%. Similarly, the hip sagittal angle increased by 99.4%, the knee angle by 36.4%, and the elbow angle by  
Figure 2: The joint angles at various difficulty levels at the initial moment of the takeoff phase. (**A**) Upper trunk twist frontside angle.