## 4 Discussion
### Frontal Plane  
In the frontal plane (Figure 14), the stroke group showed subtle compensatory responses, with increased tilt tendencies of the head, trunk, and pelvis, despite non-significant POS differences. Elevated TDISPL, MDISP, and AMPL in the head and trunk reflect exaggerated lateral shifts intended to redistribute the COM and stabilize posture. This aligns with previous findings associating excessive lateral trunk tilt with impaired hip abductor strength on the stance limb, which hinders weight transfer and increases dynamic instability [143]. The trunk plays a dual role--both stabilizing and actively contributing to postural adjustments--particularly when PC thresholds are exceeded [114; 144]. Non-linear results offer a clearer understanding of the compensatory mechanisms observed. Reduced LyE values for head and pelvis POS indicate impaired stabilization and limited adaptability during lateral weight transfers. In the pelvis, the trend towards less divergent LyE in MDISP further suggests a reliance on rigid, biomechanically constrained strategies [30]. Significant MSE reductions in head POS and DISP and trunk DISP across S1, S2, and CI reflect the poor adaptability and limited fine-tuned control in ML tasks [145; 146]. For the trunk, reduced POS MSE across all time scales further reinforces its limited ability for precise lateral adjustments, often resulting in exaggerated movements [147]. In the LLs, increased TDISPRL, MDISP, and AMPL at the ankle suggest compensatory reliance on distal segments to offset proximal instability. Reduced LyE convergence at the ankle highlights impaired dynamic control. At the knee, contrasting LyE patterns--convergent during swing and divergent during stance--suggest shifting strategies between proximal stabilization and distal compensation depending on individual impairments [41; 70]. MSE reductions in hip POS and DISP during swing (S1, S2, and CI) and in ankle POS (S2 and CI) further indicate reduced adaptability and compromised lateral stability [77]. Regarding the ULs, increased MDISP and AMPL in the elbow and wrist in the swing limb reflect compensatory adjustments across both proximal and distal segments. These amplified movements likely aim to stabilize the COM and address postural instability during lateral shifts. Greater reliance on distal segments, particularly the wrist, underscores proximal control and overall postural stability [88; 138; 148]. Non-linear measure results support this interpretation: reduced LyE convergence for wrist POS in stance reflects poor distal control, while divergent LyE in wrist DISP during swing indicates weak coordination  
Figure 14: Significant results of linear and non-linear joints analysis in frontal plane between healthy and stroke groups. LT: left tilt; ABD: abduction; AD: abduction; UD: ulnar deviation; IV: inversion; EV: evasion; SwL: swing limb; StL: stance limb; \({}^{\ast}\): significant linear differences; \({}^{\ast}\): significant LyE differences; \({}^{\ast}\): significant MSE differences. between proximal and distal segments. These findings align with evidence that trunk compensatory movements often offset deficits in UL motor dysfunction [149]. MSE reductions in shoulder (S2 and CI) and elbow (CI) POS further point to limited adaptability across temporal scales [150], reinforcing the interdependence of proximal and distal UL control, with the shoulder acting as a stabilizer to compensate for impaired postural control [151]. In the transverse plane (Figure 15), the exaggerated rotational patterns observed in the stroke group--as reflected by increased TDISPL, MDISP, and AMPL--likely represent compensatory strategies to stabilize the COM during dynamic tasks [142]. However, these rotations may compromise segmental coordination and exacerbate instability during weight transfers [152; 153]. Similar findings have linked excessive rotational movements to impaired intersegmental control and reduced neuromuscular adaptability in stroke survivors [41; 154].