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M. Puchinger, N. Babu Rajendra Kurup, M. Gföhler:
"Performance of a manual wheelchair propulsion device optimized for the musculoskeletal system of the upper limbs - preliminary results";
Talk: 8th World Congress of Biomechanics, WCB 2018, Dublin; 2018-07-08 - 2018-07-12; in: "8th World Congress of Biomechanics", (2018), 1 pages.

The wheelchair is one of the most commonly used assistive devices for enhancing the mobility of physically disabled persons. Non-ergonomic joint ranges and high repetitive loads applied to the upper limbs during the discontinuous movement of manual wheelchair propulsion cause a high risk of injuries for long-term manual wheelchair users [2]. Furthermore, the stroke in push-rim propulsion is characterized by low mechanical efficiency [3]. In this study, a novel wheelchair propulsion device was developed and tested, based on a handle-based propulsion movement that was computationally optimized for the musculoskeletal system of the upper extremities [4].

The optimized handle path was realized by a sliding guide mechanism that is mounted on each side of a conventional wheelchair instead of the armrests. A handle mounted to a length-adjusting crank, that rotates around the center point of the path, follows the sliding guide. The propulsion torque is transmitted to the wheelchair´s back wheels via timing belts with a gear ratio of 2:1, and a special pulley layout allows to adapt the crank centre position to the user´s anthropometric lengths. Tests were done on a test rig with adjustable resistance power equipped with a force measurement handle and a motion capturing system, applied forces and kinematics were captured. Five healthy subjects each performed 10 propulsion cycles at 1.2 m/s average linear velocity at 20W, 30W and 40W resistance power, fraction effective force (FEF, tangential force component divided by total force) as well as propulsion efficiency (PMEASURED/PIDEAL) were calculated for all cycles.

The results with the optimized propulsion device showed an FEF of 67% at 20W that increased to 78% at 40W, while conventional pushrim propulsion reaches 75% [5]. The propulsion efficiency reached 58% and was almost constant over the different power levels. Joint ranges at shoulder, elbow and wrist joints all stayed within the ergonomic ranges during the whole propulsion cycle.

First tests on the novel propulsion device have shown promising results for the effective force slightly above standard pushrim propulsion in combination with ergonomic joint ranges throughout the propulsion cycle, what will highly contribute to avoiding injuries. Next step will be inverse dynamic calculations to determine muscle and joint loads, and further tests with wheelchair users that will include recording of metabolic energy consumption to show the potential of the optimized propulsion movement. The compact design of the novel propulsion mechanism makes it also suitable for every day activities.

Rehabilitation, Rollstuhl, wheelchair, Antrieb, propulsion