Measuring and modeling active maximum fingertip forces of a human index finger

The present paper develops a model of "active" fingertip forces of a human index finger that allows the maximum fingertip force to be calculated for any specified position of the finger. The proposed model extends a passive fingertip force model by considering the mobility of the fingertip in terms of its deformation. The model selects the smaller force of the following two forces: the maximum force calculated using the musculoskeletal model and the maximum force calculated using the maximum deformation depth of the fingertip that lies within the ranges of motion of all the joints. A further extension of the previous passive fingertip force model is that a nonlinear relationship between muscle length and exerted force is considered. Maximum active fingertip forces were measured for three subjects and compared with the forces calculated using the proposed model and the previous model. The results of our model were in good agreement with the measured forces in contrast with the large values obtained using the passive fingertip force model.