arXiv Machine Learning

Staged Multi-Agent Training for Human-Exoskeleton Co-Adaptation: Simulation-Based Learning and Real-World Metabolic and Biomechanical Validation

The paper presents a Staged Multi-Agent Training (SMAT) method that jointly trains a musculoskeletal human model and a hip-exoskeleton controller in simulation to learn coordinated assistance strategies accounting for human-device co-adaptation. The resulting policy was transferred to a physical hip exoskeleton and tested on eight healthy adults without subject-specific retraining, showing a 19.7% reduction in net metabolic rate compared to a passive device and a positive-power ratio of 0.984 across walking speeds and terrains. These findings demonstrate that simulation-based multi-agent co-adaptation can yield a single transferable exoskeleton policy that provides meaningful physiological benefits in real users.

arXiv Machine Learning
Aug 4

Staged Multi-Agent Training (SMAT) for Hip Exoskeletons: Metabolic and Biomechanical Validation of a Simulation-Trained Co-Adaptive Controller

arXiv:2608. 00715v1 Announce Type: cross Abstract: Learning-based controllers can deliver exoskeleton assistance after training entirely in physics-based simulation, yet few controllers that address human-device co-adaptation have been validated on real users by whole-body metabolic measurement, the standard benchmark for assistive walking.

By Yifei Yuan, Jakob Wolf, Ghaith Androwis, Xianlian Zhou
arXiv Machine Learning
Sep 18

UniExo: Unified Multi-Skill Policies for Musculoskeletal Locomotion and Co-Adaptive Exoskeleton Control

UniExo is a framework that builds a single, multi-skill musculoskeletal human policy by distilling four imitation experts—walking, turning, running, and backward walking—into one network guided by a skill latent. The human policy is fine‑tuned with reinforcement learning on transition sequences, achieving a 94.7% tracking success rate on unseen clips and greater robustness to perturbations. A hip exoskeleton controller is then co‑adapted with this human policy via multi‑agent reinforcement learning, enabling it to assist across four treadmill speeds and a continuous route of all four skills without explicit mode switching.

By Yifei Yuan, Jakob Wolf, Ghaith Androwis, Xianlian Zhou
arXiv Machine Learning
Sep 21

Beyond Kinematics: Benchmarking Simulation Fidelity for Muscle-Driven Imitation Learning

The paper compares two leading motion‑imitation reinforcement learning pipelines—HyFyDy, which uses detailed musculotendon modeling, and MuJoCo, which focuses on computational speed. Using the same human motion‑capture and EMG data, both pipelines reproduce kinematics similarly, but HyFyDy’s muscle activation predictions align more closely with experimental EMG (RMSE 0.164, r = 0.4) than MuJoCo’s (RMSE 0.344, r = 0.11). The authors conclude that HyFyDy’s higher physiological realism makes it currently more suitable for musculoskeletal modeling, though both systems need further development for GPU‑parallelizable environments and robotic assistive‑device design.

By Ayah G. Ahmad, Claire E. Borden, Maegan Tucker
arXiv Machine Learning
1d ago

Transformer-Based Trajectory Prescription for sEMG-Optimizing Robot-Mediated Rehabilitation

This study introduces a transformer-based model that personalizes robot-mediated rehabilitation by mapping surface electromyography (sEMG) signals to contact force trajectories. Using a transformer encoder-decoder with rotary positional embeddings and flow matching, the model predicts trajectories with less than 8% error on unseen tasks and users, and can be fine-tuned within a single therapy session. Live tests show participants achieve target neuromotor activations with only 15% error, demonstrating the feasibility of activation-targeted trajectory prescription.

By Gabriel Parra, Kimia Khoshnami, Daniel S. Brown, Laura A. Hallock
arXiv Machine Learning
Sep 11

Reflex-Informed Neuromuscular Reinforcement Learning for Muscle-Driven Locomotion

The paper introduces a Reflex-Informed Neuromuscular Reinforcement Learning framework for muscle-driven locomotion. It combines a fixed phase-dependent reflex controller with a reinforcement learning policy that adjusts reflex gains and thresholds for hip swing, knee support, and ankle propulsion. Experiments show the method produces physiologically plausible walking with improved kinematic accuracy, dynamic consistency, symmetry, and stride consistency, and remains robust to muscle weakness and perturbations without retraining.

By Jian Zhou, Xingyu Zhang, Rui Ma, Yu Cao, Shane Xie, Zhi-qiang Zhang
arXiv Machine Learning
Aug 19

Lambda-Hold Control: Human-Like Movement Emerges from a Minimal Task Reward in Predictive Musculoskeletal Simulation

The paper introduces the λ-hold controller, a minimal-task-reward approach inspired by the equilibrium-point hypothesis, to train a muscle-actuated skeletal model for human-like sprinting. By fixing each muscle’s EP threshold length λ over gait-phase intervals, the controller dramatically reduces the action space and the frequency of policy queries, enabling efficient exploration and learning within an hour of training. This method demonstrates that physiologically grounded control can produce realistic human motion in predictive musculoskeletal simulations.

By Jun Hyuk Lee, Chihyeong Lee, Jooeun Ahn
arXiv Machine Learning
Jun 5

OLIVE: Online Low-Rank Incremental Learning for Efficient Adaptive Exoskeletons

arXiv:2606. 05234v1 Announce Type: cross Abstract: Wearable exoskeleton systems hold promise for restoring mobility in individuals with physical impairments, yet most existing controllers rely on static gait policies that lack the ability to adapt to dynamic real-world environments or individual user characteristics.

By Dong Liu, Yanxuan Yu, Ben Lengerich, Tony Geng, Ying Nian Wu
arXiv Machine Learning
Aug 4

Rapid Embodiment Adaptation for Quadrupedal Locomotion

arXiv:2608. 01506v1 Announce Type: cross Abstract: Humans readily adapt their movements as their bodies change through aging, injury, or load carrying, but learning-based robot policies often break when hardware properties shift.

By Dichen Li, Bo Ai, Nico Bohlinger, Jan Peters, Hao Su, Henrik I. Christensen