This pilot study explored how muscle activation influences the pattern recognition of tactile cues delivered using electrical stimulation (ES) during each 10% window interval of the normal walking gait cycle (GC). Three healthy adults participated in the experiment. After identifying the appropriate threshold, ES as the haptic cue was applied to the gastrocnemius lateralis (GL) and biceps brachii (BB) of participants walking on a treadmill. Findings revealed variable recognition patterns across participants, with the BB showing more variability during walking due to its minimal activity compared to the actively engaged GL. Dynamic time warping (DTW) was used to assess the similarity between muscle activation and electro-stimulated haptic perception. The DTW distance between electromyography (EMG) signals and muscle recognition patterns was significantly smaller for the GL (4.87 ± 0.21, mean ± SD) than the BB (8.65 ± 1.36, mean ± SD), showing a 78.6% relative difference, indicating that higher muscle activation was generally associated with more consistent haptic perception. However, individual differences and variations in recognition patterns were observed, suggesting personal variability influenced the perception outcomes. The study underscores the complexity of human neuromuscular responses to artificial sensory stimuli and suggests a potential link between muscle activity and haptic perception.

Human-in-the-loop (HITL) optimization can personalize exosuit assistance, but respirometry-based cost functions require bulky equipment, and proxy-based alternatives often require additional sensors or leave their relationship with metabolism unquantified. Our previous onboard-sensor approach optimized a single objective based on positive mechanical power (PMP). This exploratory study investigated whether stride time (ST), a gait response measured by the exosuit’s thigh-mounted inertial sensors, better represents metabolic reduction. Using grid-search data from three participants walking at 1 m/s on a 5° incline with a hip extension exosuit (six subject-day cases), we evaluated PMP, ST, and their combination by multiple linear regression, termed the multi-variable cost function (MVCF), with leave-one-subject-out cross-validation. ST predicted metabolic reduction numerically better than PMP (r = 0.63 ± 0.14 vs. 0.51 ± 0.37), and the MVCF performed best (r = 0.68 ± 0.11; lowest mean absolute error), although no difference was statistically significant. The MVCF, computed solely from onboard sensors, served as the objective of Bayesian HITL optimization in five participants. The optimized assistance significantly reduced net metabolic rate by 13.3%, 7.5%, and 5.2% versus power-off, no-suit, and biomimetic conditions, respectively. Combining device-side mechanical power with human-side gait timing may provide an onboard-sensor cost function grounded in measured metabolic data.

Cable-driven hip exosuits are designed to deliver assistive torques during locomotion. However, most studies focus on assistance in a single plane, even though hip mechanics are inherently multiplanar. This study investigates whether modulation of proximal and distal cable anchor-point locations can systematically alter the distribution of hip assistive torque across anatomical planes. To characterize and estimate three-dimensional torque, we propose a geometric model that incorporates empirically identified correction terms. The model was evaluated using a hip–thigh phantom across 12 anchor configurations and 17 joint-angle conditions, resulting in 204 experimental cases. The results show that anchor-point modulation systematically redistributes assistive torque among the sagittal, frontal, and transverse planes, demonstrating that changes in cable routing can generate distinct multiplanar torque profiles. The model captured major trends and directional characteristics of the torque, with strongest agreement observed for the $M_z$ component, for which the mean absolute percentage error ranged from 4.7% to 10.1%. Estimation errors increased under conditions of greater cable wrap, reflecting the influence of torsion and compliance effects not explicitly represented. These findings establish anchor-point modulation as a practical method for achieving multiplanar hip assistance and provide a foundational empirical baseline for extending cable-driven assistance beyond conventional sagittal-plane operation.