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Pubmed for Handhelds

PUBMED FOR HANDHELDS

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  • Title: Effect of handrim velocity on mechanical efficiency in wheelchair propulsion.
    Author: Veeger HE, van der Woude LH, Rozendal RH.
    Journal: Med Sci Sports Exerc; 1992 Jan; 24(1):100-7. PubMed ID: 1548983.
    Abstract:
    To study the effect of tangential speed of the handrims independent of external power output on gross mechanical efficiency (ME), nine able-bodied subjects performed wheelchair exercise tests on a stationary ergometer. The ergometer allowed for measurement of torque and three-dimensional forces on the rims and tangential velocity of the rear wheels. The experiment comprised two series of submaximal tests against constant external power outputs (0.25 and 0.50 W.kg-1) and four wheelchair speeds (0.83, 1.11, 1.39, and 1.67 m.s-1), which simulated a wheelchair speed of 1.67 m.s-1 and mechanical advantages of 0.43-0.87. ME stayed below 10.5% and changed inversely with speed of movement of the handrims. Peak torques on the right handrim stayed even with speed, leading to a significant increase in peak power output. Energy losses owing to braking torques at the beginning and end of the push phase increased with handrim speed but hardly exceeded 5 W. The effective force component applied to the handrims was below 71% of the magnitude of the total force vector and dropped up to 13% with increasing handrim speed. It is suggested that an ineffective direction of forces on the rims might (partly) be responsible for the low ME and for a decrease in ME in relation to tangential handrim velocity. This suggestion is discussed from a number of theoretical perspectives. It is concluded that the use of handrims with a lower mechanical advantage will increase wheelchair propulsion efficiency.
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