Modulation of Trunk Stimulation to Improve Efficiency of Manual Wheelchair Propulsion
1Bailey S, 1Foglyano K, 1Lombardo L, 2Triolo R
1Louis Stokes Cleveland VA Medical Center, Cleveland, , USA; 2Case Western Reserve University/Cleveland VA Medical Center, Cleveland, OH, USA
During manual wheelchair (MWC) propulsion, the trunk flexes and extends throughout the propulsion cycle  to assist the arms in creating the mechanical power for movement. However, MWC users with paralysis of core muscles are often unable to assist/resist excessive forward or backward lean to stabilize the torso. This results in inefficient propulsion mechanics, which can lead to shoulder problems and difficulties navigating challenging terrains.
Constant stimulation of the paralyzed hip/trunk muscles of individuals with SCI improves MWC propulsion efficiency on level terrain at self-selected speeds by stiffening the torso so the arms can more effectively transmit forces and moments to the pushrim. However these advantages disappear during sprints and on ramps . Appropriate timing of stimulation with the propulsion cycle may allow MWC users to better move or directionally stabilize their trunks, increase pushing efficiency and improve upper extremity mechanics during these challenging tasks. Thus, the arms could be utilized for propulsion without the additional burden of controlling trunk posture.
MWC propulsion consists of 2 main phases: contact phase where MWC users lean forward with their hands on the pushrims and stabilize against backwards trunk movement, and recovery phase where MWC users pull their trunks and arms back to prepare for the next push. An accelerometer  can detect the transition periods between each phase and trigger appropriate stimulation to the hip and trunk muscles for maximum pushing efficiency and improved biomechanics. During contact, a low level of stimulation is applied to stabilize the trunk while still allowing forward lean. Features of the sensor signals predicting the transition to recovery then activate a higher level of stimulation to arrest excessive forward lean and assist return to upright posture in preparation for the next stroke.
With a wireless accelerometer similar to a Fitbit worn on the wrist, stimulation was modulated during propulsion in 1 volunteer with a T4, AIS A SCI. Pushing with modulated stimulation was rated “very easy” (+3 on the 7-point User Ratability Scale) compared to “very difficult” (-3) without stimulation. Modulated stimulation increased propulsion speed on level ground (1.42 m/s vs 1.37 m/s without stimulation) with comparable pushing mechanics (peak force and mean fraction effective force). Greater than 95% of phase transitions were detected accurately by the accelerometer (± 2 SD of those measured by an instrumented pushrim). Baseline data from 3 additional MWC users suggest a similar implementation is feasible and can be generalized.
Simple wrist-worn sensors can detect the phase transitions of MWC propulsion instead of elaborate, laboratory-only instrumented pushrims. Modulating trunk and hip activation during propulsion has the potential to improve propulsion efficiency and mechanics, while being preferred by users. We are currently evaluating the system during challenging activities such as sprinting and negotiating ramps.
Support: Rehabilitation Research & Development Service of the U.S. Department of Veterans Affairs, Project A1204-R.
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