An evaluation of hand pressure distribution and forearm flexor muscle contribution for a power grasp on cylindrical handles

In this study, a two-dimensional biomechanical model was developed to calculate the forearm flexor tendon tension from the pressure data on the palmar side of the hand. Laboratory measurements were conducted to evaluate hand pressure distribution pattern while grasping cylindrical handles of various sizes. From these pressure data and the biomechanical model, tensions for the long finger tendons of the flexor digitorum profundus (FDP) muscle and for the long finger tendons of the flexor digitorum superficialis (FDS) muscle were calculated, and the contributions of the forearm flexor muscles to the total grasp force in power grip were estimated. Twenty-three Force Sensing Resistors (FSR) were placed on the palmar surface of the hand. Five cylindrical handles with cross-sectional diameters of 2.2, 2.8, 3.5, 4.2, and 5.05 cm were tested. Each subject exerted 0% to 100%, in increments of 10%, of his own maximum grasp force on each of the five experimental handles. The results showed that pressure was not distributed uniformly in the hand. All the handles tested, except the 2.2 cm diameter handle, had similar pressure distribution patterns. The pressure values on the distal phalanges were significantly the highest and decreased proximally. Middle fingers had the highest average pressure values and little fingers had the lowest average pressure values. Index fingers and ring fingers were not significantly different from each other. The pressure sensor located at the distal phalanx of the middle finger had the highest average pressure value among all of the 23 pressure sensors. Tendon tension of the FDS was significantly higher than that of the FDP. On the average, the FDS and the FDP contributed 61.50% and 38.50% to the total grasp force, respectively. Tendons of the middle fingers experienced the highest tension while that of the little fingers experienced the lowest tension. On the average, the index finger contributed 20.94% to the total grasp force, the middle finger 35.64%, the ring finger 26.33%, and the little finger 17.09%