## 4 Discussion
### Joint Dynamics  
Linear and non-linear findings indicate distinct compensatory mechanisms and impaired dynamic stability during GI. Similarly to CoP results, the stroke group exhibited increased variation but reduced adaptability and complexity, pointing to less efficient, more constrained motor control strategies compared to healthy individuals. This interplay between elevated linear measures (e.g., TDISPL, AMPL) and diminished non-linear indicators (e.g., LyE, MSE) offers a more nuanced understanding of post-stroke motor strategies. In the sagittal plane (Figure 13), although POS differences in the head, trunk, and pelvis were not statistically significant, the observed patterns suggest subtle compensatory mechanisms, often undetectable by static measures [108]. These findings likely reflect heterogeneity within the stroke group, influenced by individual differences in motor impairment severity, stroke chronicity, and long-term compensatory habits [109; 110]. Significant increases in TDISPL, MDISP, and AMPL across all segments--particularly the trunk and pelvis--highlight that compensations in stroke survivors are more pronounced in movement magnitude and variability rather than static positioning [111]. The stroke group demonstrated a tendency toward head FLE, contrasting with the EXT preference observed in healthy individuals. While not statistically significant, this pattern suggests a common post-stroke strategy to address impaired PC and maintain gaze stabilization [112; 113]. Head FLE shifts the COM anteriorly, disrupting biomechanical alignment and increasing reliance on trunk and pelvic compensations to maintain stability [114]. This anterior displacement imposes greater demands on trunk stabilization and may compromise the activation of the trunk extensors, which are essential for APAs during GI [41; 115]. Forward head posture has also been linked to reduced proprioceptive input, which further limits adaptability in postural adjustments [116; 117]. Compensatory mechanisms in the stroke group were reflected in significantly higher TDISPL values across all segments (head, trunk, and pelvis), reflecting greater movement amplitudes as an adaptative response to postural instability due to impaired APAs [91]. However, the increased magnitude of variation, particularly in MDISP and AMPL for the trunk and pelvis, reflects the reliance on exaggerated FLE-EXT movements to stabilize the body, which can reduce efficiency by shifting the COM further from optimal biomechanical alignment [88]. Excessive anterior pelvic tilt, a commonly reported compensatory mechanism in stroke survivors, may partially counterbalance deficits in proximal trunk control and hip extensors [118]. However, this strategy is energetically inefficient and further compromises stability by shifting the COM anteriorly [119]. These findings align  
Figure 13: Significant results of linear and non-linear joint analysis in the sagittal plane between healthy and stroke groups. EXT: extension; FLE: flexion; RV: retroversion; DF: dorsiflexion; SwL: swing limb; StL: stance limb; \({}^{*}\): significant linear differences; \({}^{*}\): significant LyE differences; \({}^{*}\): significant MSE differences. with previous research linking compensatory trunk displacements to inefficient and poorly coordinated motor actions during GI [8; 120; 121]. Non-linear measures showed less negative and more convergent LyE values in head and pelvis POS, indicating relative segmental stability [35]. However, significant MSE reductions across S1, S2, and CI suggest that this comes at the expense of adaptability. These reductions highlight compromised rapid, fine-grained adjustments and adaptability across multiple temporal scales [122; 123], suggesting a rigid strategy for head stabilization during weight shifts. This rigidity increases the reliance on the trunk and pelvis for compensatory adjustments, reflecting diminished neuromuscular flexibility--a common characteristic of post-stroke compensatory behaviours [38].