Trunk muscle activity during wheelchair ramp ascent and the influence of a geared wheel on the demands of postural control.

OBJECTIVES To quantify levels of torso muscular demand during wheelchair ramp ascent and the ability of a geared wheel to influence trunk muscle activity. DESIGN Repeated-measures design. Each participant completed manual wheelchair ramp ascents for each combination of 4 ramp grades (1:12, 1:10, 1:8, and 1:6) and 3 wheel conditions (in gear, out of gear, and a standard spoked wheel) in a block randomized order by wheel condition. SETTING Biomechanics laboratory. PARTICIPANTS Healthy novice wheelchair users (N=13; 6 men) from a university student population. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Peak electromyographic activity, expressed as a percentage of maximal voluntary isometric contraction (MVIC) of the abdominals, latissimus dorsi, and erector spinae during ramp ascent. Temporal location of peak electromyographic activity (EMG) within a propulsive cycle and integrated electromyographic activity for a single propulsive cycle. RESULTS Abdominal peak activity increased 13.9% MVIC while peak posterior trunk muscle activity increased 4.9% MVIC between the shallowest and steepest ramp grades (P<.05). The geared wheel prevented increased peak activity of the rectus abdominis and external oblique (P>.05). Only peak electromyographic timing of the erector spinae was influenced during the push phase by increasing ramp slope. CONCLUSIONS Increased trunk muscular demand as a result of increasing ramp slope is required to enhance stiffness of the spinal column and provide a stable base during manual propulsion. Manual wheelchair users with compromised activity capacity, compromised abdominal muscle strength, or both, may be able to navigate more difficult terrains while using a geared wheelchair wheel because of reduced demands from the abdominal musculature in the geared wheel condition.