Towards Implementing a Real-time Deformable Human Muscle Model in Digital Human Environments

Abstract

The current state of the art digital human models are a visual proxy for humans in part due to the advances in computer graphics. They perform with biomechanical accuracy that mimics real human motion. Models such as Santos® have a biomechanically accurate skeleton driving the motion, which in turn controls the deformation of a flexible skin for added realism, all in real time. However, these models lack realistic musculoskeletal systems that respond in real time to biomechanical motion. They require varying levels of pre-processing before motion can be applied to them, thus preventing the real time effect; muscle models need to be flexible and deformable, which in computer simulations generally translates to higher computation requirements. By combining advances in computer graphics, especially the fast rendering game graphics capability, with known literature on musculoskeletal modeling, a preliminary full body musculoskeletal system that deforms in real time is presented along with the skeleton and skin. Given the biomechanical studies focus of digital humans, the model implemented centers on the mathematical articulation, and not the graphical volumetric representation, of actual musculoskeletal systems. As such, each muscle is defined as a line that starts at an origin position, determined from anatomy, and ends at the corresponding insertion position, while wrapping as needed around cylindrical obstacles that emulate the minimum bulges required for that line to be at the centroid of the actual equivalent muscle. For each muscle, the origin position, insertion position and obstacle parameters (position, rotation, and scale) have to be obtained relative to key joints for accurate articulation. This was done manually on a per-muscle basis for 126 muscles, and can be extended to any anthropometric avatar. With this initial real-time model, there is potential for a quicker assessment of the effect of muscles on human task performance, leading to a complete model that deforms in real time.