Kat Steele presented at the International Society of Biomechanics Technical Group on Computer Simulation in Edinburgh, Scotland on July 11, 2015. This study quantifies how traditional methods for estimating muscle activity in musculoskeletal simulation (e.g., minimizing sum of squared muscle activations) fails to accurately predict muscle activity for individuals with cerebral palsy. This research will help to guide the development of new methods to quantify patient-specific changes in neuromuscular control.