## 2 Materials and Methods
### Motion Capture and Data Processing
Joint angles were quantified as follows: the shoulder joint angle was defined as the Euler angle of the upper arm reference frame relative to the upper trunk reference frame, with the rotation sequence of horizontal adduction-abduction, adduction, and internal-external rotation; the hip joint angle was defined as the Euler angle of the thigh reference frame relative to the lower trunk reference frame, using the sequence of flexion-extension, adduction-abduction, and internal-external rotation; elbow and knee angles were defined as the angular deviation between the longitudinal axes of adjacent segments; the upper trunk twist angle was calculated as the angular displacement between the shoulder and hip transverse lines measured about their midpoint axis. This study specifically focused on the anterior joints, defined as the side of the athlete's body facing the direction of travel during takeoff. The moment of inertia for each body segment was calculated using a multi-step approach, in which the subject's body parameters were first scaled based on a formula derived from standard human model data [25], incorporating adjustments for individual variations in weight and height. \[I_{i}=I_{0}^{i}\frac{ML}{M_{0}L_{0}} \tag{1}\]  
where \(I_{0}^{i}\) (kg\(\cdot\)m\({}^{2}\)) is each body's moment of inertia of the standard human model \(M_{0}\) (kg) is the weight of the standard human model; \(M\) (kg) is the weight of the subject; \(L_{0}\) (m) is the torso length of the standard human model; \(L\) (m) is the torso length of the subject; \(I_{i}\) (kg\(\cdot\)m\({}^{2}\)) is the moment of inertia of the joint limb's center of mass corresponding to the center of gravity; The rotation axes were identified by analyzing joint velocities, decomposed into components along the sagittal, coronal, and transverse planes. The dynamic calculation of the moment of inertia was performed throughout the motion sequence by applying the parallel axis theorem to each body segment at discrete time intervals, considering the segment's mass and its position relative to the rotation axis. \[I_{k}^{i}=I_{i}+M^{i}(I^{i})^{2} \tag{2}\]  
where \(I_{i}\) (kg\(\cdot\)m\({}^{2}\)) is the moment of inertia of the joint limb's center of mass corresponding to the center of gravity; \(M^{i}\) (kg) is the mass of a particular limb; \(I^{i}\) (m) is the distance from the limb's center of gravity to the body's center of gravity; \(I_{k}^{i}\) (kg\(\cdot\)m\({}^{2}\)) is the moment of inertia of the joint limb around the axis of rotation. The total body moment of inertia was then determined by summing the contributions of individual segments. \[I_{k}=\sum\limits_{i=1}^{n}I_{k}^{i}dn \tag{3}\]  
where \(I_{k}\) (kg\(\cdot\)m\({}^{2}\)) is the moment of inertia of the entire human body at a certain moment. The rotational kinetic energy of an athlete was calculated through the angular velocity and the moment of inertia of each body segment. \[E=\sum\limits_{i=1}^{n}\frac{1}{2}I_{i}\omega_{i}^{2} \tag{4}\]  
where \(\omega_{i}\) (rad/s) is the angular velocity of the \(i\)-th segment and \(E\) (J) is rotational kinetic energy of the human body.