Surface electromyography activity of trunk muscles during wheelchair propulsion

Background Trunk instability due to paralysis can have adverse effects on posture and function in a wheelchair. The purpose of this study was to record trunk muscle recruitment patterns using surface electromyography from unimpaired individuals during wheelchair propulsion under various propulsion speed conditions to be able to design trunk muscle stimulation patterns for actual wheelchair users with spinal cord injury. Methods Fourteen unimpaired subjects propelled a test wheelchair on a dynamometer system at two steady state speeds of 0.9 m/s and 1.8 m/s and acceleration from rest to their maximum speed. Lower back/abdominal surface electromyography and upper body movements were recorded for each trial. Based on the hand movement during propulsion, the propulsive cycle was further divided into five stages to describe the activation patterns. Findings Both abdominal and back muscle groups revealed significantly higher activation at early push and pre-push stages when compared to the other three stages of the propulsion phase. With increasing propulsive speed, trunk muscles showed increased activation (P < 0.0001). Back muscle activity was significantly higher than abdominal muscle activity across the three speed conditions (P < 0.0005), with lower back muscles predominating. Interpretation Abdominal and back muscle groups cocontracted at late recovery phase and early push phase to provide sufficient trunk stability to meet the demands of propulsion. This study provides an indication of the amount and duration of stimulation needed for a future application of electrical stimulation of the trunk musculature for persons with spinal cord injury.