Shoulder joint contact force during lever-propelled wheelchair propulsion

ROBOMECH Journal, Oct 2015

The aim of this study was to obtain quantitative results about shoulder contact force during wheelchair lever propulsion when the gear ratio of the lever propulsion mechanism is changing. The effect of the gear ratio on the shoulder contact force was investigated for few different wheelchair loading. For the experiments we designed a special mechatronic wheelchair simulator that allowed the simulation of different gear ratios of the wheelchair lever propulsion mechanism and simulation of different road inclinations. The same simulator was also used for simulation of a hand rim propelled wheelchair. We conducted also a handrim propulsion experiment and used the results from it for comparison with the lever propulsion data. Four nondisabled male adults with no prior wheeling experience participated in the experiment. In the first tests, a lever propelled wheelchair was simulated with the simulator. The target speed of the wheelchair was set to 2 km/h. For the test, the gear ratio was varied from 1.5 to 1/1.5. A load torque was applied to the rear wheels to imitate road inclinations of 0°, 2° and 4°. In the second part of the test, the simulator was structured to simulate a handrim propelled wheelchair. The participants were asked to keep the same speed (2 km/h) and the simulator was set sequentially to imitate climbing a ramp inclined on 0°, 2° and 4°. Kinematic data of the body were collected by a motion capture system. Kinetic data such as hand force and driving torque, were measured by instrumented wheels with incorporated six-axis force sensor. The intersegmental joint forces and moments were calculated from the obtained kinematic and kinetic data via inverse dynamics analysis procedure. Muscle forces were computed from the measured joint moments by using an optimization approach. Shoulder joint contact force, which indicates the joint surface loading, was computed as a synthetic vector of the intersegmental force for shoulder joint acquired from the inverse dynamics analysis and the compressive forces from muscles, tendons, ligaments and cartilages crossing the shoulder joint. It was observed that the decrease of the gear ratio causes increased cycle frequency and reduces the shoulder joint contact force. Result showed that the shoulder joint contact force during lever propulsion with a gear ratio 1/1.5 was up to 70 % lower than the shoulder joint contact force during handrim propulsion. The results from this study could be used in the design of new lever propulsion mechanisms that reduce the risks of secondary shoulder disorders and increase user’s comfort.

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Shoulder joint contact force during lever-propelled wheelchair propulsion

Sasaki et al. Robomech J Shoulder joint contact force during lever-propelled wheelchair propulsion Makoto Sasaki 0 Dimitar Stefanov 2 Yuki Ota 0 Hiroki Miura 1 Atsushi Nakayama 1 0 Graduate School of Engineering, Iwate University , Morioka, Iwate , Japan 1 Department of Intelligent Systems Engineering, Ichinoseki National College of Technology , Ichinoseki, Iwate , Japan 2 School of Science and Technology, Middlesex University , London , UK The aim of this study was to obtain quantitative results about shoulder contact force during wheelchair lever propulsion when the gear ratio of the lever propulsion mechanism is changing. The effect of the gear ratio on the shoulder contact force was investigated for few different wheelchair loading. For the experiments we designed a special mechatronic wheelchair simulator that allowed the simulation of different gear ratios of the wheelchair lever propulsion mechanism and simulation of different road inclinations. The same simulator was also used for simulation of a hand rim propelled wheelchair. We conducted also a handrim propulsion experiment and used the results from it for comparison with the lever propulsion data. Four nondisabled male adults with no prior wheeling experience participated in the experiment. In the first tests, a lever propelled wheelchair was simulated with the simulator. The target speed of the wheelchair was set to 2 km/h. For the test, the gear ratio was varied from 1.5 to 1/1.5. A load torque was applied to the rear wheels to imitate road inclinations of 0°, 2° and 4°. In the second part of the test, the simulator was structured to simulate a handrim propelled wheelchair. The participants were asked to keep the same speed (2 km/h) and the simulator was set sequentially to imitate climbing a ramp inclined on 0°, 2° and 4°. Kinematic data of the body were collected by a motion capture system. Kinetic data such as hand force and driving torque, were measured by instrumented wheels with incorporated six-axis force sensor. The intersegmental joint forces and moments were calculated from the obtained kinematic and kinetic data via inverse dynamics analysis procedure. Muscle forces were computed from the measured joint moments by using an optimization approach. Shoulder joint contact force, which indicates the joint surface loading, was computed as a synthetic vector of the intersegmental force for shoulder joint acquired from the inverse dynamics analysis and the compressive forces from muscles, tendons, ligaments and cartilages crossing the shoulder joint. It was observed that the decrease of the gear ratio causes increased cycle frequency and reduces the shoulder joint contact force. Result showed that the shoulder joint contact force during lever propulsion with a gear ratio 1/1.5 was up to 70 % lower than the shoulder joint contact force during handrim propulsion. The results from this study could be used in the design of new lever propulsion mechanisms that reduce the risks of secondary shoulder disorders and increase user's comfort. Lever-propelled wheelchair; Musculoskeltal model; Shoulder joint contact force - Wheelchair handrim propulsion comprises a push phase in which the user applies force to the handrims to generate propulsion torque around the wheel axle, and a recovery phase when the user releases the hands from the handrims to initiate the next push phase. However, the mechanical efficiency of the wheelchair propulsion is quite low, usually about 10  % [1–3]. The propulsion torque transmitted to the driving wheel depends on the tangential component of the force applied to the handrim by user’s hand, handrim radius, and the torque around the point of hand contact. In general, the hand force in tangential direction toward the handrim contributes to the wheelchair propulsion because the handrim has only one degree of freedom which is its rotation around the rear wheel axis [4]. However, wheelchair user needs to impose a significant force in normal direction toward the handrim in order to create a frictional force and achieve © 2015 Sasaki et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. efficient wheelchair propulsion. Usually, a significant part of the energy for wheelchair propulsion is used for generation of the normal force. The normal force does not contribute to the torque transferred to the driving wheel and decreases the energy efficiency. Propulsion efficiency also depends on the manner of application of propulsion force used by the individual and it is reduced additionally due to the intermittent character of the force applied to the handrims. Groot et al. investigated the ef (...truncated)


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Makoto Sasaki, Dimitar Stefanov, Yuki Ota, Hiroki Miura, Atsushi Nakayama. Shoulder joint contact force during lever-propelled wheelchair propulsion, ROBOMECH Journal, 2015, pp. 13, 2, DOI: 10.1186/s40648-015-0037-8