Locomotor Adaptation to an Asymmetric Force on the Human Pelvis Directed Along the Right Leg

Abstract

In this work, we study locomotor adaptation in healthy adults when an asymmetric force vector is applied to the pelvis directed along the right leg. A cable-driven Active Tethered Pelvic Assist Device (A-TPAD) is used to apply an external force on the pelvis, specific to a subject's gait pattern. The force vector is intended to provide external weight bearing during walking and modify the durations of limb supports. The motivation is to use this paradigm to improve weight bearing and stance phase symmetry in individuals with hemiparesis. An experiment with nine healthy subjects was conducted. The results show significant changes in the gait kinematics and kinetics while the healthy subjects developed temporal and spatial asymmetry in gait pattern in response to the applied force vector. This was followed by aftereffects once the applied force vector was removed. The adaptation to the applied force resulted in asymmetry in stance phase timing and lower limb muscle activity. We believe this paradigm, when extended to individuals with hemiparesis, can show improvements in weight bearing capability with positive effects on gait symmetry and walking speed.

A System for Simple Robotic Walking Assistance With Linear Impulses at the Center of Mass

“…Our values appear to fall within the range of errors in anterior-posterior forces obtained from studies with cable robots (within-step RMSE 2% BW in [23], [25], and 0.92% BW in [24]). Another point of comparison is the study from Grabowski and Kram [52] that describes an elastic tether with a rudimentary but elegant force indicator for manually towing a person during running.…”

“…The optimal stiffness appears to be of a similar order of magnitude as stiffnesses used in other cable robots (2280 Nm −1 in [23]; 2500 Nm −1 in [24]). Interestingly, the steel spring with the highest stiffness (2577 Nm −1 ) resulted in a within-step RMSE that was approximately twice as high as the Thera-band spring with equivalent stiffness.…”

“…The load cell was mounted at the attachment point with the participant to avoid underestimating or overestimating the applied forces due to oscillating mass from the tether components (elastic element or mechanical fuse). Certain cable robot studies use a similar configuration [21], [23], [39], and others appear to position load cells away from the participant [24], [25], [28] or estimate the forces based on the elongation of a spring [22]. The control station consists of an input-output interface (HuMoTech) and a real-time computer (SpeedGoat, Liebefeld, Switzerland) that runs a controller in Simulink (MathWorks, Data 1).…”

“…A research group from Columbia University developed different multi-cable systems that can apply forces and moments in different directions at the pelvis [23]- [26]. A motorized version of their system can apply a net force that dynamically tracks the direction of the ground reaction force of the legs and could be used to elicit certain desirable compensatory after-effects when the device is turned off in individuals with hemiparesis [24]. Simha et al [22] developed a robotic system with two tethers that can apply net forward or backward horizontal forces at the waist, and that can rapidly adjust the force levels from step to step.…”

A Novel Approach to Apply Gait Synchronized External Forces on the Pelvis Using A-TPAD to Reduce Walking Effort

“…The A-TPAD has the advantage of using cables which do not add external mass/inertia on the user. In addition, the A-TPAD can be easily customized to use different cable routing configurations to apply a desired force profile [27]–[29]. In comparison, existing rigid-link pelvic devices do not provide control of all six DOFs and thus add undesired human-robot joint misalignment and mobility constraints during walking.…”