# A Comparative Analysis of IMUs and Optical Systems in Layup Shot Biomechanics
## 4 Discussion
### Between-Condition Analysis  
The paired-sample \(t\)-test revealed no significant differences between the Vicon and Xsens systems in detecting changes between conditions for both jump height and take-off angle. Specifically, the differences detected by Vicon (jump height: 0.028 m; take-off angle: 2.03\({}^{\circ}\)) and Xsens (jump height: 0.022 m; take-off angle: 2.91\({}^{\circ}\)) were not statistically significant (\(p\geq 0.238\) and \(p\geq 0.225\), respectively). These findings reinforce the reliability of both systems in consistently detecting condition-induced changes in performance metrics.  
Due to the inability to confirm joint angle accuracy between the two systems, a between-condition analysis was conducted to evaluate Xsens' reliability in capturing condition-specific biomechanical changes. This analysis revealed a mean offset of 1.3\({}^{\circ}\) between systems, with most joint angles differing by less than 1.0\({}^{\circ}\). In line with the prior literature, an RMSD threshold of \(\leq\)5\({}^{\circ}\) was considered indicative of excellent agreement [24; 25]. Our results showed that the majority of joint angles, particularly in the sagittal plane, fell within or near this threshold, supporting the practical use of IMUs in applied sport settings where high relative precision is desirable, but absolute accuracy is not always critical. Prior research has noted that IMUs may not replicate raw joint angles as precisely as optical systems, especially during complex, multi-planar movements [50; 51]. Therefore, assessing condition-specific trends rather than direct system comparisons offers a more suitable approach for evaluating movement adaptations.  
The condition-based SPM analysis (Figures 8 and 9) supported these findings by identifying comparable cluster sizes and locations for defended and undefended conditions across both systems. The analysis demonstrated that Xsens was capable of detecting similar magnitudes of condition-based differences in shoulder joint angles as Vicon, particularly during the layup task. While absolute measurement precision could not be confirmed, Xsens reliably detected changes induced by defensive conditions.  
This result is significant for tasks involving complex upper-limb mechanics, such as layup shots, shooting, and passing under defensive pressure, where shoulder positioning and rotation are critical. The ability of Xsens to capture condition-induced changes underscores its practical application in performance analysis and training. Its portability and capacity to provide real-time feedback make it particularly advantageous for applied sports settings.  
These findings further demonstrate that Xsens effectively captures relative biomechanical changes under varying conditions. Minor differences in timing or magnitude of significance clusters, such as Xsens showing slightly broader time windows of significant effects, may reflect subtle discrepancies in precision or noise sensitivity. Nonetheless, consistent kinematic differences between defended and undefended conditions were observed across both systems, with critical-\(t\) values and \(p\)-values confirming the statistical robustness of the results.  
By focusing on within-system, condition-specific changes, the potential for confounding factors introduced by inter-system variability is minimized. This ensures that observed trends in joint angles, timing, and coordination patterns can be reliably attributed to experimental conditions rather than inconsistencies between measurement platforms, thus providing strong validation for the use of Xsens in layup mechanics analysis.