Abstract
Objective: The main objective of the tests conducted was to analyze the position variability of the human body’s center of gravity during propelling the wheelchair, and to demonstrate the properties enabling the description of this variability by means of plane figures with a symmetry axis. A secondary objective was to show the impact of the used manual propulsion type and the wheelchair inclination angle in relation to the plane on the dimensions of the position variability areas of the center of gravity. Method and materials: Three patients participated in the research representing 50 centiles of anthropometric dimensions. Each patient carried out fifteen measurement tests on three wheelchairs for three inclination angles of the wheelchair frame in relation to the level. Each measurement test consisted of five propulsion cycles for which the positions of the center of gravity were determined with the sampling frequency of 100 Hz. The measured positions of the center of gravity were approximated with ellipses containing 95.4% of the measurements conducted, assuming their dimension scaling basis in the form of the double value of standard deviation defined based on the registered results. Results: Based on the measurements conducted, the average values of five ellipses parameters were determined for nine cases in which a variable was the type of wheelchair propulsion and its inclination angle in relation to the level. The area of the highest variability of the position of the center of gravity was measured for the wheelchair with a multispeed transmission. The average dimensions of the ellipse semi-axis amounted to 108.53 mm for the semi-axis a and 29.75 for the semi-axis b, the average position of the ellipse center amounted to x = 114.51 mm and y = −10.53 mm, and the average inclination angle of the ellipse α amounted to −6.92°. The area of the lowest variability of the position of the center of gravity was measured for the wheelchair with a hybrid transmission. In this case, the average dimensions of the ellipse semi-axis amounted to 64.07 mm for the semi-axis a and 33.85 for the semi-axis b; whereas, the average position of the ellipse center amounted to x = 245.13 mm and y = −28.24 mm, and the average inclination angle of the ellipse α amounted to −0.56°.
Highlights
According to the World Health Organization (WHO) data, 10% of the world’s population is constituted by people with disabilities
As far as the multispeed wheelchair is concerned, the patient chose a transmission ratio that was comfortable for such a patient, and it was used during all the measurement tests
The conducted research demonstrated that during propelling the manual wheelchair along a straight section, there is the symmetric distribution of the position points of the center of gravity on the horizontal plane
Summary
According to the World Health Organization (WHO) data, 10% of the world’s population is constituted by people with disabilities. A considerable portion of this group includes people with motor disabilities who must use wheelchairs. A wheelchair with a patient constitutes an anthropotechnical system described with a range of interrelated biomechanical parameters, such as speed [2], acceleration [3], muscle activity [4] and the position of the center of gravity [5]. One of the most important biomechanical parameters is the position of the center of gravity. Many biomechanical analyses simplify it to a single fixed point. Such an approach is an excessive simplification because a human body moves continuously during the wheelchair operation
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