Cable-routing geometry as a design variable for multiplanar hip assistance in a single-actuator soft exosuit

Cable-driven soft exosuits for gait assistance are predominantly sagittal-plane devices, yet pathological gait involves coordinated deviations across all three anatomical planes. This study experimentally evaluated whether cable-routing geometry alone, within a single-actuator hip exosuit, can produce measurable multiplanar hip effects during walking. Ten healthy, exosuit-experienced male adults walked on a treadmill under five conditions: one matched unpowered control and four powered configurations that paired single-plane and multi-plane cable routing with hip-flexion and hip-extension assistance. Three-dimensional hip kinematics were compared across conditions, and exosuit-generated hip torques were estimated from subject-specific musculoskeletal models. Multi-plane routing produced phase-dependent kinematic changes concentrated in the transverse plane. Relative to unassisted walking, multi-plane flexion assistance increased hip internal rotation (3.6°, p = 0.0002), multi-plane extension assistance increased hip external rotation (1.8°, p = 0.0095), and single-plane flexion assistance produced a smaller but significant increase in external rotation (1.1°, p = 0.0463). Frontal-plane differences were not significant for any comparison with unassisted walking, so the hypothesized larger frontal-plane deviations under multi-plane routing were not supported. Multi-plane routing also produced greater sagittal-plane hip excursion than single-plane routing. Overall gait-trajectory similarity between single-plane and multi-plane routing was comparable in most comparisons and differed significantly only in the hip frontal plane during extension assistance. The estimated torques indicated that multi-plane routing introduced larger frontal- and transverse-plane components while the sagittal-plane component remained dominant. These findings show that cable-routing geometry alone can shape phase-localized hip kinematics, reaching significance in the transverse plane, without adding actuators. The effect magnitudes were small and near the measurement uncertainty of the capture system. The all-male, exosuit-experienced sample limits generalizability, so relevance to clinical populations remains to be tested. Cable-routing geometry is therefore proposed as a candidate rather than an established design variable for multi-dimensional assistance in soft exosuits.