The jar opening movement requires a complex integration of digits and adequate grasp strength. Unfortunately, many young females have difficulty achieving this task. The opening direction may be an important element related to the force efficiency of hand. However, few studies have been conducted on this topic with an actual human movement. The purpose of this study was to investigate the effect of jar twisting direction on hand kinetics during a maximum voluntary twist. It was hypothesized that changing the twist direction would alter the results of hand kinetics and that an optimal twist direction could be found for opening a jar. Thirty-six healthy young females with mean age, body weight, and height of 23.5 ± 3.6 years, 53.1 ± 6.0 kg, and 160.4 ± 4.3 cm, respectively, were recruited. A custom jar instrument was fabricated to record the kinetics of hand and digit groups. All participants performed jar twisting movements in the clockwise and counterclockwise directions. The results showed that the overall torque and resultant force of right hand increased when a clockwise twist was applied. The resultant force and torque shares of the thumb also increased for the clockwise twist even though those of the middle-ring-little digit group showed no difference and those of the index digit decreased. The index digit and thumb contributed the least and most effort, respectively, for both twisting directions. The thumb was the main force digit. Normal force was the main component of force for all digit groups. The force projections showed that other digit groups not only antagonized the thumb but also one another. The results supported the hypothesis that there were kinetics differences for digits for the two twisting directions. Jar lids could be opened more efficiently in the clockwise direction and kinetics of each digit group also provided as a precursor to jar design modification.
All Science Journal Classification (ASJC) codes
- Biomedical Engineering