Grip Force Simulations Using an Instrumented Cadaver Forearm
Authors: Andris Freivalds, Shihyun Park, Joonho Changa, Neil Sharkeyb
Abstract: Forceful tendon exertions while gripping hand tools may be one of the factors leading to the development of work-related musculoskeletal disorders (WRSMDs). Estimated tendon forces from biomechanical hand models are unreliable and need to be validated. A novel neuromuscular grip simulator using a cadaver forearm was developed consisting of 1) an aluminum frame supporting the specimen, 2) a motion-delivery unit with stepper motors applying force to the FDP and FDS tendons, 3) a data acquisition unit for force transducers, 4) a camera system measuring finger joint angles, and 5) an operating system to control the complete simulator. Of special necessity were an adjustable fixation system, the Wristjack and the use of freeze clamps with liquid nitrogen to insure a tight bond between the slippery tendons and the force delivery system. Key experimental factors varied were five different diameter handles and the ratio of FDP/FDS tendon forces. The results on two specimens showed an inverse relationship of handle size and grip force, with the smallest handle size of 30 mm being best. A 3:2 ratio (40% FDS) provided the best efficiency and the largest gripping. Internal tendon averaged 6.2 times the external forces,matching the biomechanical model predictions of Kong, 2004. 72% of the power grip was concentrated on the distal phalanges. Overall, this novel simulator served well for understanding internal tendon forces.
Keywords: Grip Force, Tendon Forces, Cadaver Forearm Simulations, Handle Size
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