The objectives of this study were to investigate the effect of handle shape on the grip force distribution in the hand and on the muscle forces during maximal power grip tasks. Eleven subjects maximally grasped 3 handles with different external shapes (circular, elliptic, and double-frustum). A handle dynamometer, equipped with both a force sensor and a pressure map, was used to record the forces exerted at the hand/handle interface. The finger and wrist joint postures were also computed from synchronized kinematic measurement. These processed data were then used as input of a biomechanical hand model to estimate muscle forces. The results showed that handle shape influences the maximal grip force, the grip force distribution, and the finger joint postures. Particularly, we observed that the elliptical shape resulted in a 6.6% lower maximal grip force compared with the circular and double-frustum handle. Concomitantly, the estimated muscle forces also varied significantly according to the handle shape, with up to 48% differences for the flexor digitorum superficialis muscle for example. Interestingly, different muscle coordination strategies were observed depending on the handle shape, therefore suggesting a potential influence of these geometrical characteristics on pathological risks such as tendonitis.
Jérémy Rossi, Benjamin Goislard De Monsabert, Eric Berton and Laurent Vigouroux
Barry Thombs and David Sugden
Forty Down syndrome children in five groups between the ages of 6 and 16 years were examined on a number of manual tasks. These involved a variety of hand actions during peg displacement, transportation, manipulation, and relocation. A number of age related changes were noted. With increasing age there was an almost linear increase in the use of precision as opposed to power grips, offering the older children a greater range of responses. In general the older children were more consistent in their approach than younger children, although this was not a linear increase and was also dependent on the type of task. On a number of speed measures, the older children were faster at performing the task, although small subject numbers and within-group variability prevented some differences from being significant.