Human Motion Analysis
Many different disciplines use motion analysis systems to capture movement and posture of the human body. Basic scientists seek a better understanding of the mechanisms that are used to translate muscular contractions about articulating joints into functional accomplishment, e.g. walking. Increasingly, researchers endeavor to better appreciate the relationship between the human motor control system and gait dynamics.
In the realm of clinical gait analysis, medical professionals apply an evolving knowledge base in the interpretation of the walking patterns of impaired ambulators for the planning of treatment protocols, e.g. orthotic prescription and surgical intervention and allow the clinician to determine the extent to which an individual’s gait pattern has been affected by an already diagnosed disorder. With respect to sports, athletes and their coaches use motion analysis techniques in a ceaseless quest for improvements in performance while avoiding injury. The use of motion capture for computer character animation or virtual reality (VR) applications is relatively new. The information captured can be as general as the position of the body in space or as complex as the deformations of the face and muscle masses. The mapping can be direct, such as human arm motion controlling a character’s arm motion, or indirect, such as human hand and finger patterns controlling a character’s skin color or emotional state. The idea of copying human motion for animated characters is, of course, not new. To get a convincing motion for the human characters in Snow White, Disney studios traced animation over film footage of live actors playing out the scenes. This method, called rotoscoping, has been successfully used for human characters. In the late’70’s, when it began to be feasible to animate characters by computer, animators adapted traditional techniques, including rotoscoping.
Generally, motion analysis data collection protocols, measurement precision, and data reduction models have been developed to meet the requirements for their specific settings. For example, sport assessments generally require higher data acquisition rates because of increased velocities compared to normal walking. In VR applications, real-time tracking is essential for a realistic experience of the user, so the time lag should be kept to a minimum. Years of technological development has resulted in many systems and can be categorized in mechanical, optical, magnetic, acoustic and inertial trackers. The human body is often considered as a system of rigid links connected by joints. Human body parts are not actually rigid structures, but they are customarily treated as such during studies of human motion.