Wrist Twisting Strength of four Year Olds: Product Packaging Implications

Abstract

The research reported in this paper is the second of a two phase study related to consumer packaging. In the first phase, the subjects consisted of 100 elderly males and 100 elderly females. The results of this phase of the study were reported at the 1983 HFS meeting in Norfolk. In this phase of the study, the subjects were 100 four-year old boys and 100 four-year old girls. The purpose of the study was to measure their wrist-twisting strength or the torque that could be exerted on jar lids of various diameters. To accomplish this, a standard torque-wrench was modified so as to accept eight container lids whose diameters ranged from 27 mm to 123 mm. Each subject performed the wrist-twisting task on each lid four times - twice clockwise and twice counter-clockwise. Using torque as the dependent measure, analyses of variance were computed for the boys and girls separately. The results showed that direction of rotation - clockwise or counterclockwise, was not significant. However, lid as a source of variation was. When age, body weight, height, grasp, lateral prehension, and hand length, breadth, and spread were correlated with the wrist-twisting strength, it was found that for the boys, grasp was critical for all eight of the lids and hand length and spread were equally important. For the females, the individual's body weight plus grasp were significantly correlated with torque for all eight lids. And whereas age and weight were significantly correlated with the torque that could be exerted on seven of the eight lids for the girls, they were only modestly related to torque for the males. However, like the boys, hand spread was significantly correlated with torque among the females. Findings related to reports of the Consumer Products Safety Commission and the Safety in Packaging Act are discussed and a proposal is advanced suggesting that the use of containers whose lids have diameters of 60 mm and larger would be too large for a four-year old hand to open while they could be readily opened by the elderly consumer.^*