Biomechanics and Physiology for Propelling Wheelchair Uphill Slope

A vertical slope of sidewalks significantly inhibits to the mobility of manual wheelchair users in their daily life. International guidelines of the vertical slope are specified approximately 4% or 5% (1:20) gradient or less as preferred, and allow 8.3% (1:12) as its maximum when it is impossible. Relevant research of the physical strain for wheelchair users with pushing on slopes, and the validity assessment of slope guidelines have been investigated. However, the analysis for the effect of a slope distance and their transient performance are still remained. The purpose of this study is to clarify the physiological and biomechanical characteristics of manual wheelchair users that propelling a wheelchair on an uphill slope. We measured these data by a metabolic analysis system, a heart rate monitor system and an instrumented wheelchair wheel. Sixteen unimpaired subjects (non-wheelchair users) were examined to investigate the effect of a long slope with 120m distance and 8% gradient. And five wheelchair users with cervical cord injury were examined to evaluate the influence of different gradients (5%, 6.7%, 8.3%, 10% and 12.5%) with 3m length in laboratory. Our experimental results of the long slope showed that wheelchair propulsion velocity and power increased considerably at the beginning of the slope where the peak mean value of them were 0.96 m/s and 70.8W and they decreased linearly to 0.55m/s and 33.6W at final interval. A mean oxygen uptake and heart rate were increased as the distance increased and their results indicated the extremely high exercise intensity at a final interval that were 1.2liter /min and 152bpm. While wheelchair pushing cadence reduced after an initial interval, mean of strokes per10m increased to compensate the decrease of upper limb's power. The results of different gradients indicated that the normalized power of subjects with cervical cord injury was significant difference between each subject in the ability to climb a slope. Mean normalized power were 0.23W/kg on a 5% slope, 0.24W/kg on 6.7%, and 0.26W/kg on 8.3% respectively. Based on these findings, we examined the relationship between the theoretical normalized power and the lowest velocity to climb a slope, and we might indicate the ability to push on an uphill slope for the persons with manual wheelchair user.