Effect of Context-Dependent Modulation of Trunk Muscle Activity on Manual Wheelchair Propulsion.

OBJECTIVES To reliably determine the two main phases of manual wheelchair (MWC) propulsion via a simple wearable sensor and to evaluate the effects of modulated trunk and hip stimulation on MWC propulsion during the challenging tasks of ramp assent and level sprint. DESIGN An offline tool was created to identify common features between wrist acceleration signals for all subjects that corresponded to the transitions between the contact and recovery phases of MWC propulsion. For one individual, the acceleration rules and thresholds were implemented for real-time phase-change event detection and modulation of stimulation. RESULTS When pushing with phase-dependent modulated stimulation, there was a significant (p<0.05) increase in the primary speed variable (5-6%) and the subject rated pushing as "moderately or very easy". In the offline analysis, the average phase-change event detection success rate was 79% at the end of contact and 71% at the end of recovery across the group. CONCLUSIONS Signals from simple, wrist-mounted accelerometers can detect the phase transitions during MWC propulsion instead of elaborate and expensive, instrumented systems. Appropriately timing changes in muscle activation with the propulsion cycle can result in a significant increase in speed, and the system was consistently perceived to be significantly easier to use.