Existing isometric force models can be used to predict tension in the finger flexor tendon, however, they have not been validated by experimental observations. In a previous study (Dennerlein 1997) the authors measured and reported in vivo tendon force of human flexor digitorum superficialis (FDS) of eight subjects during isometric pinch tasks. The estimated ratios of tendon force to fingertip force were larger than predicted by the theoretical models of Chao (1989) Harding, (1993) and Weightman & Amis (1982). Furthermore, FDS tendon tensions of pulp pinch postures (4 subjects) were significantly higher than for tip pinch postures. Models in the literature do not predict this difference. Our goal is to implement a 2-D tendon force model and to develop a new model better representing the causes of the observed differences.