Fall Down Steps
Marc GreenParts of Steps In talking about steps, there is a standard terminology. Each step consists of two basic parts, the "tread," the flat horizontal surface, and the "riser," the vertical surface. The horizontal area before the first tread and after the last tread is called the "landing." Stairs often have a nosing, which extends out from the tread edge. The tread depth minus the nosing is the "going." Lastly, the rise divided by the tread depth gives the "pitch," which can be converted into degrees by taking the inverse tangent.
Gait & Balance Safe stair descent may be described as a controlled fall in which a walker must perform two tasks. First, the walker must accurately move the foot so that it clears the upper tread edge and lands squarely on the next, lower tread. Second, the walker must maintain balance while standing on one leg and shifting weight forward and downward. The starting point for understanding stair descent is the problem of maintaining balance. The behavior of staying in upright posture, even when standing quietly, is complex. Most people take posture maintenance for granted because it is performed automatically, requiring little or no conscious thought. In fact, it is a complex operation that requires integration of body movement with several perceptual abilities. The body's weight is distributed around an imaginary point called the "center of gravity" (CoG). Balance occurs when the center of gravity is located within a "base of support," usually the two feet. When standing quietly, the body maintains a "static balance" but when walking or using a stairway the balance is "dynamic" because the CoG is moving relative to the base of support. Maintaining balance requires active effort. Even when standing quietly, the body makes small movements causing sway that must be quickly corrected to prevent tipping over. The amount of sway depends on several factors, including the breadth of the center of support (feet together is a less stable stance than feet apart) and age (sway is greater for the old than for the young.) Usually, people make the corrections quickly and automatically, unaware that compensatory movements are constantly taking place. The corrections needed for balance require two pieces of information: 1) the gravitational axis and 2) the location of the body in space. Three sense modalities, vestibular, visual and somatosensory, provide the information required for postural maintenance. The vestibular system detects changes of head position with respect to gravity. It is centered in the inner ears and consists primarily of three semicircular canals, filled with fluid, that are positioned at right angles. When the head moves, the liquid shifts in the canals, signaling a change in position with respect to gravity. The visual modality detects changes in the visual scene that occur during sway. Just as bumping a camera changes the information imaged on the film, sway changes the image that falls on the eye and reveals change in position. The somatosensory modality consists of tactile and proprioceptive perception. Tactile sense ("sense of touch") creates perception of felt position. It signals properties of the surface that the feet are contacting, slope, roughness, etc. Proprioception is the ability to sense the motion and position of the body through sensory organs located inside the body muscles, tendons and joints. It is possible, for example, to know the position of a leg, even with the eyes closed. Vision and proprioception work together to sense and to correct deviations from balance. Once a person begins walking, the center of gravity changes with respect to the base of support. People walk with a "gait," a systematic pattern of movements that maintains balance despite the constant relative motion of the center of gravity and base of support. People use different gaits, depending on the surface that they are ambulating. Walking down steps Templer (1992) described the typical stair descent gait. As shown in Figure 2, the gait consists of several distinct stages. When a person descends from one step to the next (or from the landing to the first step), he/she performs a standard series of actions (See Figure - from Muybridge, 1955):
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