## 4 Discussion  
The study investigated the influence of joint angle time histories on ball release speed during an overarm throwing task for one experienced pitcher. Joint angle changes at the shoulder were clearly important to overarm throwing ball release speed, as all three joint angle time histories at the shoulder had a substantial effect on ball release speed (more than 3 m/s difference), whilst the joint angle time history that had the largest effect on ball release speed was forearm extension/flexion at the elbow (Table 1). The sequence of joint angle changes that had the largest positive effect on ball release speed were trunk extension/flexion, upper arm external/internal rotation, and forearm extension/flexion. In contrast, the joint angle time histories that had only a small effect on ball release speed (i.e., less than 3 m/s difference in resultant ball speed) were: pelvis (extension/flexion, adduction/abduction, external/internal rotation) trunk (adduction/abduction, external/internal rotation), scapula (elevation/depression, retraction/protraction), right forearm (adduction/abduction, pronation/supination), right hand (extension/flexion, ulnar/radial deviation). Starting at the origin of the simulation model, the first joint angle in the kinematic/kinetic chain that had a substantial effect on ball release speed was trunk extension/flexion, with the trunk firstly extending and then flexing in the last 100 ms prior to ball release (Figure 4). Using trunk movements \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Constant Joint Angle**} & \multirow{2}{*}{\begin{tabular}{c} **Mean Difference** \\ **in \(x\)-Axis (m/s)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Mean Difference** \\ **in \(y\)-Axis (m/s)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Mean Difference** \\ **in \(z\)-Axis (m/s)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Difference in** \\ **Resultant** \\ **Speed (m/s)** \\ \end{tabular} } \\ \hline Pelvis extension/flexion & \(-\)0.03 & 1.36 & \(-\)0.59 & +1.35 \\ Pelvis adduction/abduction & 0.39 & \(-\)0.07 & \(-\)0.11 & \(-\)0.11 \\ Pelvis external/internal rotation & \(-\)0.25 & \(-\)1.65 & \(-\)2.04 & \(-\)1.53 \\ Trunk extension/flexion & 0.86 & \(-\)5.25 & \(-\)0.53 & \(-\)5.22 \\ Trunk addiction/abduction & 2.08 & \(-\)0.01 & \(-\)0.76 & 0.04 \\ Trunk external/internal rotation & 0.31 & \(-\)2.75 & \(-\)1.63 & \(-\)2.67 \\ Scapula adduction & \(-\)0.29 & 0.05 & 0.30 & 0.03 \\ Scapula external/internal rotation & 0.23 & \(-\)1.39 & \(-\)2.26 & \(-\)1.25 \\ Right upper arm extension/flexion & \(-\)1.50 & 3.11 & \(-\)3.32 & +3.40 \\ Right upper arm adduction/abduction & 1.09 & 4.75 & \(-\)2.26 & +4.84 \\ Right upper arm external/internal rotation & 12.15 & \(-\)9.82 & \(-\)4.85 & \(-\)6.03 \\ Right forearm extension/flexion & \(-\)11.77 & \(-\)14.86 & \(-\)1.57 & \(-\)10.15 \\ Right forearm adduction/abduction & 0.33 & \(-\)0.35 & \(-\)0.19 & \(-\)0.37 \\ Right forearm pronation/supination & \(-\)0.02 & 0.07 & 0.07 & 0.05 \\ Right hand extension/flexion & 0.49 & \(-\)2.08 & \(-\)4.55 & \(-\)1.59 \\ Right hand ulnar/radial deviation & 0.01 & 0.01 & \(-\)0.01 & \(-\)0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Change in ball release speed as each joint angle was kept constant. to initiate the throwing motion is a key movement pattern that is also seen in other overarm throwing tasks, such as cricket fast bowling where trunk flexion has been identified as one of four factors that contributes to ball release speed [29]. The second key joint was the shoulder where all joint angle changes affected ball release speed; the upper arm remained abducted by over 90 deg throughout the throw, along with being extended and externally rotated before rapidly starting to flex and internally rotate in the last 50 ms prior to ball release. This is similar to cricket fast bowling [29], where the trunk flexes forward and the bowling arm is left circumducted behind the body.