Postural stability of humans.

摘要

This thesis investigates the interrelationships between various parameters involved in shipboard postural stability, such as muscle force, centre of pressure, and centre of mass. A series of tasks, including quiet standing on a steady deck, sagittal manual materials handling consisting of lifting and lowering a rigid load, ascending and descending stationary ship stairs, and balancing on a motion platform simulating unsteady deck motion representative of quiescent periods aboard a frigate operating in high sea state were performed by six fit subjects. Each subject was instrumented such that synchronized time-varying foot pressure distributions, postural configuration as sensed optically using 34 passive retro-reflective markers and eight infra-red cameras, and EMG signals of twelve muscle groups potentially relevant to postural stability were collected. Post-processing techniques were implemented and refined to extract relevant data as well as to compute derived data including centre of mass position and muscle activation. A comprehensive correlation analysis was performed illuminating the relationships that exist between individual muscle activation signals, centre of pressure movement, and centre of mass movement.;The results support many previous observations in shipboard postural stability literature and provide additional insight that directly supports understanding of postural stability and the development of biodynamic postural stability models. The results show the importance of taking a systems engineering approach to the study of postural stability, rather than the approach that has typically been taken; which has been to study one or two parameters in isolation. The results also show that centre of pressure is maintained within only a small fraction of the base of support during the tasks performed. This may imply that motion induced interruptions will occur prior to centre of pressure reaching the actual physical boundary of the base of support as well. This would support recent findings by Langlois et al. [1] where motion induced interruptions were observed in cases where traditional models did not predict them. The results also strongly suggest the need for articulated postural stability models with variable stiffness, actuated joints in order to model complex tasks and accommodate the substantial changes to centre of mass and mass moment of inertia that are possible in the human body.