Modulation of anticipatory postural adjustments of gait using a portable powered ankle-foot orthosis

Prior to taking a step, properly coordinated anticipatory postural adjustments (APAs) are generated to control posture and balance as the body is propelled forward. External cues (audio, visual, somatosensory) have been shown to facilitate gait initiation by improving the magnitude and timing of APAs in Parkinson's disease (PD), but the efficacy of these cueing strategies has been limited by their inability to produce the forces required to generate an appropriate APA. To date, mechanical cueing paradigms have been relatively underexplored. Using healthy young adults, we investigated the use of a portable powered ankle-foot orthosis (PPAFO) to provide a modest torque at the ankle as a mechanical cue to initiate gait. Subjects were instructed to initiate gait in five test conditions: (1) self-initiated in running shoes [baseline-shoe], (2) self-initiated trial in unpowered passive PPAFO [baseline-passive], (3) with acoustic go-cue in passive PPAFO [acoustic-passive], (4) acoustic go-cue and simultaneous mechanical assist from powered PPAFO [acoustic-assist], and (5) mechanical assist cue only [assist]. APA characteristics were quantified using ground reaction force (GRF), center of pressure (COP), and electromyography (EMG) data. Mechanical cueing significantly increased medial-lateral COP and GRF peak amplitude, and decreased GRF time to peak amplitude, COP and GRF onset times, and time to toe off. Mechanical cueing conditions also demonstrated consistent bimodal EMG behaviors across all subjects. Overall, these data suggest that the mechanical assist from the PPAFO can significantly improve APA timing parameters and increase APA force production in healthy young adults.