Effects of Boundary-Based Assist-as-Needed Force Field on Lower Limb Muscle Synergies During Standing Posture Training

Abstract

The boundary-based assist-as-needed (BAAN) force field is widely used in robotic rehabilitation and has shown promising results in improving trunk control and postural stability. However, the fundamental understanding of how the BAAN force field affects the neuromuscular control remains unclear. In this study, we investigate how the BAAN force field impacts muscle synergy in the lower limbs during standing posture training. We integrated virtual reality (VR) into a cable-driven Robotic Upright Stand Trainer (RobUST) to define a complex standing task that requires both reactive and voluntary dynamic postural control. Ten healthy subjects were randomly assigned to two groups. Each subject performed 100 trials of the standing task with or without assistance from the BAAN force field provided by RobUST. The BAAN force field significantly improved balance control and motor task performance. Our results also indicate that the BAAN force field reduced the total number of lower limb muscle synergies while concurrently increasing the synergy density (i.e., number of muscles recruited in each synergy) during both reactive and voluntary dynamic posture training. This pilot study provides fundamental insights into understanding the neuromuscular basis of the BAAN robotic rehabilitation strategy and its potential for clinical applications. In addition, we expanded the repertoire of training with RobUST that integrates both perturbation training and goal-oriented functional motor training within a single task. This approach can be extended to other rehabilitation robots and training approaches with them.

Muscle synergies for multidirectional isometric force generation during maintenance of upright standing posture

“…Our study provides a prospective basis for potential application of voluntary and multi-directional force generation to assess muscle coordination in the context of CoP sway control during steady-state upright standing. Specifically, the examination of muscle synergies emerges as a valuable metric for motor assessment, given that alterations in the number, structure, and recruitment of muscle synergies have the potential to discern the control and coordination of postural muscles during stable upright standing among a variety of physiological and pathological changes in the nervous system (Safavynia et al 2011 ; Ting et al 2015 ), and link to scientific knowledge about the functions of the neural mechanisms of posture affected by injury, impairment (Milosevic et al 2017 ; de Kam et al 2018 ; Yang et al 2019 ) or as a consequence of exercise and training (Allen et al 2017 ; Ai et al 2023 ). Furthermore, it lays the foundation for exploring synergy control-based approaches in human-computer interaction environments to promote recovery and improvement of motor skills in individuals with postural deficits (Berger et al 2013 , 2022 ; Berger and d’Avella 2014 ; Borish et al 2021 ).…”

Characterizing the Effects of Adding Virtual and Augmented Reality in Robot-Assisted Training

“…MATLAB (Mathworks, MA) was used for data preprocessing. Data collected from VICON cameras and the pressure seated mat were lowpass filtered using a fourth-order Butterworth filter with cutoff frequencies of 10 and 6 Hz, respectively [42], [43]. For the self-report data collected from questionnaires, a seven-point Likert scale was assigned to each question [39].…”

Advancements in Sensor Technologies and Control Strategies for Lower-Limb Rehabilitation Exoskeletons: A Comprehensive Review

“…Since exoskeletons require extensive human-computer interaction, the user's perception needs to be greatly considered when controlling the movement of the device. Therefore, assist-as-needed (AAN) is an important control strategy that provides appropriate assistance according to the patient's needs, leading to better results in rehabilitation and assisted walking, and is therefore receiving increasing attention from researchers of exoskeleton controllers [6,91].…”

“…This helps to increase patient motivation and participation in rehabilitation and promotes rehabilitation outcomes. By improving the dynamic stability of the exoskeleton system, patients are more stable and secure during walking and movement [91]. This helps reduce the risk of accidental falls and injuries and improves rehabilitation outcomes.…”