# A Comparative Analysis of IMUs and Optical Systems in Layup Shot Biomechanics
## 3 Results
### Statistical Parametric Mapping (SPM) Analysis  
SPM analysis was conducted to identify differences between joint angle outputs from the Vicon and Xsens systems during the layup shot. The results revealed three distinct patterns across joint angles: (1) no significant differences across participants (e.g., wrist flexion-extension motion), (2) varied responses across participants (e.g., external-internal shoulder, hip, ankle, and elbow angles), and (3) consistent differences across participants (e.g., shoulder and hip abduction-adduction angles). Knee flexion-extension joint angles exhibited high waveform agreement between the two systems across participants. However, significant differences were detected during the initial phase of the movement. The SPM critical threshold (\(t\) = 3.321) was exceeded between 0% and 10% of the task (Figure 4), with a supra-threshold cluster probability of \(p\) = 0.001, indicating a significantly more extended angle detected from the Vicon system. Ankle flexion-extension joint angle also witnessed the presence of supra-threshold clusters at some instances despite the systems' general waveform agreement (Figure 5). Significant differences were detected between 5% and 14% of the task (\(t\) = 3.391, \(p\) < 0.001), where the Xsens system reported a more dorsiflexed angle compared to the Vicon system (Figure 5a). In the external-internal joint angles, significant differences emerged at 0% to 8% and 15% to 20% of the task (\(p\) = 0.011, \(p\) = 0.013), with Xsens initially reporting a more everted angle followed by a reversal, where the Vicon system showed more eversing (Figure 5b). The remaining waveform sections displayed no significant differences. The wrist flexion-extension and ulnar-radial deviation joint angles demonstrated no significant differences between the systems. SPM critical thresholds for flexion/extension (\(t\) = 2.924) and radial/ulnar deviation (\(t\) = 3.073) were not exceeded, indicating homogeneous waveforms (Figure 6). However, differences were observed in ulnar-radial deviation joint angles for some participants during specific phases, such as take-off or the preparatory step. Figure 4: (**Top half**) a single participant example of the mean trajectories and standard deviations for the right knee joint angle of the Xsens (blue line and shaded area) and Vicon (red line and shaded area) systems during the layup shot. (**Bottom half**) The paired-samples \(t\)-test statistic SPM \(\{t\}\). The critical threshold of 3.321 (red dashed line) was exceeded at time 0–10%, with a supra-threshold cluster probability of \(p\) = 0.001 indicating a significantly more extended angle detection from the Vicon system. The shoulder flexion-extension joint angles showed minimal differences between the systems, with occasional discrepancies centred around the peak of the jump or maximum shoulder flexion. In contrast, the abduction-adduction and external-internal joint angles exhibited significant differences across participants, with no consistent pattern in timing or duration of supra-threshold clusters (Figure 7a,b). For instance, the abduction-adduction joint angles surpassed the critical threshold twice during 0% to 3% and 70% to 76% of the task (\(t\) = 3.047, \(p\) = 0.025, \(p\) = 0.044). Similarly, the external-internal joint angles displayed significant clusters occurring at varying times before and after take-off (\(t\) = 3.186, \(p\) < 0.001) despite general waveform agreement. A between-condition analysis was performed to assess the consistency of Xsens and Vicon in detecting changes between defended and undefended conditions (Table 1). Joint angles were classified into three categories based on the results of the between-condition analysis: (1) Both systems detected similar defence-induced changes within the same time windows across the time series (Figure 8a).