A computational framework for simulating and analyzing human and animal movement

An outline of the basic steps involved in the production of voluntary movement is quite simple. Commands initiated in the brain are transmitted along nerves to muscles. When activated by nerves, muscles generate forces. Muscle forces are transferred to bones and produce angular motions of the joints. When the nervous system properly coordinates the activation of many muscles, the result is smooth, purposeful movement. Scientists fascinated by human and animal movement have examined each of these steps and performed an extensive range of experiments to record neuromuscular excitation patterns, characterize muscle-contraction mechanics, describe musculoskeletal geometry, and quantify movement dynamics. However, linking detailed knowledge of neuromusculoskeletal elements to create an integrated understanding of movement remains a challenge. Computational models of human and animal movement provide a framework for integrating facts about the biology of movement. Once researchers develop and test a computer model of the neuromusculoskeletal system, they can use it to explore movement control, analyze athletic performance, and simulate treatments for musculoskeletal and neurologic disorders. Researchers need simulations to complement experimental studies because important elements of movement, including neural signals and muscle forces, are extremely difficult to measure experimentally. Developing accurate simulations of human and animal movement is challenging because of the intrinsic complexity of biologic systems. For example, the forces produced by muscles depend on their activation, length, and velocity. Muscles transmit forces through tendons, which have nonlinear properties. Tendons connect to bones that have complex geometry and span joints that have complicated kinematics. Understanding how the nervous system coordinates movement is especially difficult because many muscles work together to produce movement, and any individual muscle can accelerate all of the joints of the A COMPUTATIONAL FRAMEWORK FOR SIMULATING AND ANALYZING HUMAN AND ANIMAL MOVEMENT