People living with tetraplegia experience a significant loss of sensory and motor function; with the severity depending on their injury level and completeness. To complete tasks independently, people with tetraplegia often rely on assistive devices. To avoid upper extremity pain, designs should not require applications of force near the limits of the user's physical strength. This paper establishes a 2D biomechanical model using static equilibrium and joint torque limits to predict multidirectional strength patterns in the sagittal plane for people with C5 to C7 tetraplegia in a seated position. The results from the biomechanical model highlight the areas and directions of high strength. The strength patterns observed in this paper provide an opportunity for designers to evaluate strength requirements and take advantage of areas and directions of high strength and ensure that users are not required to apply force near their physical limit. In doing this, designs such as assistive devices can be developed that enable users with a reduction in strength to operate them independently.