There is a 73% incidence of falls among individuals with mild to moderate stroke. 37% of patients that fall sustain injury that required medical treatment. 8% sustained fractures and the risk for hip fracture is ten times higher in the stroke population. General risk of fracture is two to seven times greater following a stroke. Due to the impact falls have on the health and well being of persons with stroke, there is a substantial need to assess dynamic balance during walking in order to ascertain who is at increased risk for falls.

While little has been done to quantify balance during walking in the general population, much less has been done to quantify the effect of neurological impairment on balance during gait in persons with stroke. Approaches for determining who is at risk for falls have usually relied on clinical measurement scales as opposed to quantitative evaluation of joint power production ability. However, interpretations of these measures are based on statistical evidence and do not quantify a subject’s balance performance during walking.

To quantify and ultimately improve dynamic balance during neurologically impaired walking, it is necessary to quantify the biomechanical effects of altered or impaired joint power productions during paretic gait. These effects are relevant since a primary disability associated with post-stroke hemiparesis is the failure to make rapid graded adjustment of muscle forces. Reduction in, or ill coordinated, muscle forces result in inefficient and ineffective net joint power production. In order to quantify the biomechanical effects related to a decrease in joint power production, a detailed biomechanical simulation of the human body during perturbed walking is necessary to elaborate on experimental findings.

A simulation that can explore the effects of reduced power production on balance requires the development of a ground contact model that can explain the production of ground reaction forces and moments based on the deformation/kinematics of the foot.

The following work develops the ground contact model and the biomechanical simulation that mathematically relates reduction in joint power production to deficits in balance. Furthermore, the work investigates the role of various joints’ in maintaining balance and quantifies successful balance with a mathematical measure:​ whole body angular momentum.

To improve understanding of the relation between joint power production and balance, the simulation is subjected to an optimization procedure that results in kinematic and kinetic solutions that return whole body angular momentum to a regular limit cycle following a perturbation. Studying the return of whole body angular momentum to a regular limit cycle after a perturbation assists in understanding balance since whole body angular momentum collectively quantifies rotational velocity of the entire body about the center of mass and in order to maintain balance, the rotational velocity of the entire body is necessarily bounded.