Sangjoon J. Kim | Searcharxiv

arXiv2025

Promoting arm movement practice with a novel wheelchair armrest early after stroke: A randomized controlled trial

Chronic upper extremity (UE) impairment is common after stroke. This study evaluated Boost, a novel wheelchair-mounted rehabilitation device designed to assist individuals in UE motor recovery during inpatient rehabilitation. Thirty-five stroke inpatients were randomized to perform additional UE exercises alongside standard therapy, using either Boost or a therapist-customized booklet for self-practice. Outcomes included the UE Fugl-Meyer (UEFM) Exam, Box and Block Test, Motor Activity Log, Modified Ashworth Scale, shoulder subluxation, and shoulder pain. At baseline, mean days post-stroke were 11.9$\pm$4.6 and 13.1$\pm$5.9, and UEFM scores were 20.5$\pm$10.1 and 21.0$\pm$13.5. Intervention durations averaged 11.9$\pm$4.0 and 17.2$\pm$8.8 days, respectively. Participants in the Boost group completed 3,359$\pm$3,137 additional arm movements. No significant between-group differences were found at the three-month follow-up. However, the Boost group showed a trend toward greater UEFM improvement immediately post-intervention (11.8 vs. 6.9 points, p=0.06). Importantly, UEFM gains were predicted by the number of Boost exercises performed (p=0.02, R-square=0.34). Subgroup analysis revealed that patients with less severe impairment (baseline UEFM >21) achieved significantly greater UEFM improvements at discharge with Boost compared to controls (15.8 vs. 7.8 points, p=0.01). These findings demonstrate the feasibility of achieving thousands of additional UE practice movements while seated in a wheelchair without direct supervision during subacute rehabilitation. The added movement practice was well tolerated and may offer short-term impairment-reduction benefits, particularly in those with less severe impairment. Larger trials are needed to confirm efficacy, establish optimal dosage, and determine long-term clinical and functional benefits of Boost-assisted therapy.

q-bio.NC↗

arXiv2024

Haptic Transparency and Interaction Force Control for a Lower-Limb Exoskeleton

Controlling the interaction forces between a human and an exoskeleton is crucial for providing transparency or adjusting assistance or resistance levels. However, it is an open problem to control the interaction forces of lower-limb exoskeletons designed for unrestricted overground walking. For these types of exoskeletons, it is challenging to implement force/torque sensors at every contact between the user and the exoskeleton for direct force measurement. Moreover, it is important to compensate for the exoskeleton's whole-body gravitational and dynamical forces, especially for heavy lower-limb exoskeletons. Previous works either simplified the dynamic model by treating the legs as independent double pendulums, or they did not close the loop with interaction force feedback. The proposed whole-exoskeleton closed-loop compensation (WECC) method calculates the interaction torques during the complete gait cycle by using whole-body dynamics and joint torque measurements on a hip-knee exoskeleton. Furthermore, it uses a constrained optimization scheme to track desired interaction torques in a closed loop while considering physical and safety constraints. We evaluated the haptic transparency and dynamic interaction torque tracking of WECC control on three subjects. We also compared the performance of WECC with a controller based on a simplified dynamic model and a passive version of the exoskeleton. The WECC controller results in a consistently low absolute interaction torque error during the whole gait cycle for both zero and nonzero desired interaction torques. In contrast, the simplified controller yields poor performance in tracking desired interaction torques during the stance phase.

cs.RO↗