We propose a methodology to estimate subject-specific physiological parameters of Hill-based models of upper arm muscles. The methodology uses Hill-type candidate functions in the Fast Orthogonal Search (FOS) method to predict force at the wrist during elbow flexion and extension. To this end, surface EMG data from three muscles of the upper arm were recorded from 5 subjects as they performed isometric contractions at different elbow joint angles. Estimated muscle activation level and joint angle were utilized as inputs to the FOS model to obtain subject-specific estimates of optimal joint angle the Gaussian shape parameter for the force-length relationship for each muscle.