The overall goal of this study was to systematically estimate the physical load according to common object properties and hand postures while objects were held. The physical load was evaluated by kinematic, kinetic, biomechanical, and physiological (EMG) methods.
The specific aims of the study were 1) to investigate the hand postures commonly used in manufacturing companies, according to the use of either the right or left hand and the object properties; 2) to investigate common patterns of voluntary hand posture according to object shapes, sizes, and directions; 3) to compare and quantify the kinematic model and marker attachment method for hand posture analysis; 4) to develop a biomechanical model of the human hand in order to understand the force and moment of the finger joints associated with common hand postures and object properties; 5) to measure the physical load according to the hand posture and object properties using kinematic, kinetic, biomechanical, and physiological (electromyography) methods; 6) to verify the degree of physical load according to the hand posture and object properties.
The behavioral study found that the most commonly used hand postures were 5P (TIMRL), 5G (TIMRL), 3P (TIM), 4P (TIMR), and 2P (TI), and the choice of hand posture was affected by the object’s properties, including its shape, size, and orientation. Regarding the physical load, the hand posture greatly influenced all the variables of kinematic, biomechanical, and muscle activation. The object weight also greatly influenced the variables of kinetic and muscle activation, but did not greatly affect the kinematic variable. The object size influenced the kinematic variable and some biomechanics variables. The object shape had little influence on the kinematic, biomechanical, and muscle activation variables.
