We are working on modeling a deformable human arm to improve the accuracy of constrained reach analysis. This work is a part of the project "Crew Task Simulation for Maintenance, Training, and Safety". Crewmembers are performing constrained reaches with arm and body for both intra- and extra-vehicular activity (IVA and EVA). They tolerate a certain level of tissue deformation when compressed against a solid object such as an obstacle or the joint in an extravehicular mobility unit (EMU). We have created a deformable arm segment by measuring skin indentation as a function of applied load. In order to populate the model with reasonable tissue properties we have built a simple but effective measuring device to acquire the non-linear force-depth relation from numerous sample points on an arm surface. Given an obstacle, our goal is to determine the reachable space under a certain level of tolerable contact force. We use a finite element method based on living tissue properties and the measured force-depth relations. This work will be applied to estimate the increase in reachable volume of a crewmember an EMU for EVA operation as well as for shirt-sleeved IVA operations.