Modelling wrist-twisting strength of the elderly

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Abstract
This paper presents a biomechanical model of wrist-twisting strength and uses it to explain maximum voluntary contractile (MVC) counter-clockwise torque and force generated by elderly subjects in attempting to unscrew rough and smooth circular screw-type container lids of diameters 31, 55, 74 and 113 mm. Forty-two subjects, aged 60-97 years, were tested. The results indicated-that for-commercially available lids, torque-diameter relationship was linear up to a certain lid size (diameter), and non-linear, with a decreasing trend, beyond that size. The non-linearity was different for lids with rough and smooth grip surface. An optimal diameter for smooth lids has been proposed. For both types of grip surfaces, force magnitudes were similar up to 74 mm. Beyond this diameter the effects of surface finish were manifested. This was explained by the relationship between hand size and type of grip used at the various diameters. Implications of these results for lid design are discussed. Regression models are also presented which portray good fit to the data.

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