Robotic training of children with crouch gait improved posture and walking by enhancing muscle strength and coordination.

Balance recovery during an unexpected disturbance is a complex motor task, where part of the variability depends on the type of the perturbation itself. Despite of this, little is known to what extent adaptation mechanisms to repeated perturbations are dependent on the direction and the amplitude of the applied disturbances. Here, we used a modified version of the Active Tethered Pelvic Assist Device (A-TPAD) to apply unexpected force-controlled multidirectional waist-pull perturbations while subjects were walking. Healthy young subjects were divided into two groups and were exposed to a single training session. Each group received perturbations of different amplitudes along the Medio-Lateral (ML) or the Antero-Posterior (AP) direction. Dynamic stability was determined in both the AP and ML directions in terms of base of support (BoS) and margin of stability (MoS). Results showed: 1) an adaptation of the balance recovery reactions only for perturbations delivered along the AP directions; 2) aftereffects able to modify the control of stability during the post-training session of which type and extent depends on the direction of the perturbations previously applied; and 3) a directional and amplitude effect on the dynamic stability at the end of the balance recovery reactions.

An active Tethered Pelvic Assist Device (A-TPAD) has been presented in this paper. TPAD is a cable robot for studying force adaptation in human walking by applying external forces and moments on the human pelvis. A two stage control strategy was implemented to apply the desired force-moment profile. The controller includes (i) a quadratic programming based optimization scheme, (ii) a real-time human motion monitoring system and (iii) a PID feedback loop to plan and implement the required cable tensions. The control strategy was validated first by testing it on a dummy pelvis setup. A pilot experiment was then conducted with a human walking on a treadmill with A-TPAD. The goal was to apply a vertical downward force vector equivalent to 10% of subject's body weight (BW) at the pelvis. Results showed that the applied vertical force was acting downwards over the full gait cycle and was between 8-13% of the BW. Other force-moment components were maintained within a specified range during the experiment. Increased foot pressure was reported in the presence of vertical force. In summary, A-TPAD provides the capability of applying and controlling a desired force-moment profile on the human pelvis over a gait cycle.

In this letter, we develop an intervention to apply external gait synchronized forces on the pelvis to reduce the user's effort during walking. A cable-driven robot was used to apply the external forces and an adaptive frequency oscillator scheme was developed to adapt the timing of force actuation to the gait frequency during walking. The external forces were directed in the sagittal plane to assist the trailing leg during the forward propulsion and vertical deceleration of the pelvis during the gait cycle. A pilot experiment with five healthy subjects was conducted. The results showed that the subjects applied lower ground reaction forces in the vertical and anterior-posterior directions during the late stance phase. In summary, the current work provides a novel approach to study the role of external pelvic forces in altering the walking effort. These studies can provide better understanding for designing exoskeletons and prosthetic devices to reduce the overall walking effort.

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 after effects 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.