Common patterns of voluntary grasp types according to object shape, size, and direction

• Use of grasp type is affected by object shape, size, and orientation.
• Seven grasp types are commonly used to hold cylindrical and rectangular objects.
• Grasping and pinching with five fingers are the most frequently used hand postures.
• The larger the object, the greater number of fingers is used.

This study aimed to investigate commonly used voluntary grasp types according to object shape, size, and direction, with the participation of 50 students. The grasp type classifications consisted of grasping (G) and pinching (P) and were further subdivided based on the number and use of fingers (T, thumb; I, index finger; M, middle finger; R, ring finger; or L, little finger) and palm (P). Seven grasp types were commonly used by the participants: 5P (TIMRL), 5G (TIMRL), 3P (TIM), 4P (TIMR), 2P (TI), 4G (TIMR), and 3G (TIM). Participants most frequently held cylindrical and square pillar objects using 5G (TIMRL) and 5P (TIMRL), respectively. 3P (TIM) was commonly used to hold 1- to 4-cm objects, whereas 5G (TIMRL) and 5P (TIMRL) were commonly used to hold 8- to 12-cm objects. The up-down direction-oriented objects were commonly held with 5G (TIMRL), and the left-right direction-oriented objects were held with 2P (TI), 3P (TIM), and 5G (TIMRL). These results provide basic information regarding common patterns of human grasp types.Relevance to industryThis paper provides a guideline on the selection of hand tools in industry in terms of their shapes and sizes, so that workers can use appropriate hand postures to reduce hand stresses.