## 4 Discussion  
In this study, we measured the peak acceleration and velocity of uke's shoulder in tai-otoshi and morote-seoi-nage: two judo throws strongly implicated in shoulder injury. It was assumed that uke applied no conscious resistance when being thrown [28]. Both variables were greater in tai-otoshi than morote-seoi-nage; however, only the difference in velocity showed statistical significance. This suggests that impact loads at the shoulder are greater in tai-otoshi, and we may conclude that tai-otoshi carries a greater risk of injury to judo players. An increased peak velocity of uke's shoulder in tai-otoshi implies that they are able to be thrown quicker by tori. In tai-otoshi, tori throws uke over their lowered shoulder onto the mat in one swift movement. Conversely, in morote-seoi-nage, tori must first load uke onto their back before they are thrown onto the mat. A study by [PERSON] et al. concluded that the acceleration of uke's head in tai-otoshi was greater than in seoi-nage for similar reasons, and we could apply this to our own findings [12]. It is also worth noting that the peak velocity of uke's shoulder was recorded moments before making contact with the mat in all throws. The velocity at impact would, in theory, become zero, therefore supposing the time difference between the peak and impact velocity to be the same in both throws, a greater change in velocity suggests a greater acceleration. However, given that we did not account for the duration of throws in this study, we cannot say this with confidence. Though, such qualitative analyses might go some way in explaining our results. Accurately estimating impact forces in the absence of force plates remains challenging. Nevertheless, our findings can be used in theoretical calculations to grossly estimate the impact force. [PERSON]'s second law states the force (F) acting on an object is a product of its mass (m) and acceleration (a) [31]. Thus, if the mass of uke's shoulder was known and remained equal in both throws, it is not unreasonable to suggest that impact forces are greater in tai-otoshi. Alternatively, the work-energy principle approximates impact forces when the kinetic energy (KE) and deformation distance (s) of an object during impact is \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Tai-Otoshi** & **Morote-Seoi-Nage** & & \\ \hline  & & & \(p\) & \(d\) \\ \hline Acceleration (m/s\({}^{2}\)) & 71.6 \(\pm\) 12.4 & 67.9 \(\pm\) 9.9 & 0.655 & 0.188 \\ \hline ICC & 0.896 & 0.822 & & \\ \hline Velocity (m/s) & 5.1 \(\pm\) 0.8 & 4.5 \(\pm\) 0.6 & 0.030 * & 0.783 \\ \hline ICC & 0.995 & 0.759 & & \\ \hline \hline \end{tabular}
* Indicates a statistically significant result (\(p\) < 0.05).  
\end{table} 
Table 2: Average peak acceleration and velocity of uke’s shoulder in tai-otoshi and morote-seoi-nage. known. Again, this requires the seemingly unrealistic assumption of a constant mass and deformation distance across both throws. Our data suggests that the shoulder is subjected to greater loads in tai-otoshi, and this may be associated with an increased risk of injury. However, we acknowledge the limitations of our methodology in using our findings to calculate the impact forces, largely due to the absence of other measured variables. We are also aware that additional factors (i.e., landing angle) are heavily involved in shoulder injury mechanisms, although this was beyond the scope of the present study. For this reason, we should be careful when attempting to draw any direct conclusions regarding injury risk, and these factors ought to be accounted for in subsequent research. The study design also meant that we did not consider longer-term injury outcomes, despite no injuries being reported throughout the data collection process. In this instance, it is likely that the elite players included in our study would be familiar with nage-komi (repetitive throwing) exercises in training, and is not associated with a significant injury risk [28; 32].