A body may be stable in one direction but not necessarily in another.
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In contrast, rotary stability may be considered as a resistance to change the present state of angular motion by external torques accelerating or stopping the rotation about a given axis, or to change the angular motion from one axis to another. For upright postures with no angular motion, rotary stability would be associated with the resistance of the body to tripping over. Linear or rotary stability can be improved by various motor strategies. Even when attempting to stand as still as possible, these physiological processes will always ensure a certain degree of body sway, since the erect human body can be described as a constantly fluctuating inverted pendulum Loram and Lakie, Although during some phase of these movements, the objective of the individual may be to maintain dynamic equilibrium, be firmly established, resist change to their position, or minimize fluctuations, the individual will eventually want to change position by moving easily and sometimes suddenly.
In this regard, individuals can be considered to move along a continuum of equilibrium states Figure 1. Hence, dynamic stability is achieved during locomotion since stance periods are continuously provided CoM within BoS while the CoM projection repetitively passes through the BoS.
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Stable, unstable, and neutral states of equilibrium are typically found in rigid bodies rather than in animate objects. However, humans are highly dynamic, animate, non-rigid bodies equipped by nature with physiological mechanisms to compensate for perturbations in stationary and locomotive environments.
Although stable instability may seem like an oxymoron, individuals are often in a state of flux, which allows them to transfer smoothly from relatively stable to relatively unstable conditions change from stance to flight phase during running. Without some degree of instability, it would be impossible to move; however, without some degree of stability, it would be impossible to maintain equilibrium or to remain upright.
Thus, the state of relatively stable or metastable equilibrium is defined as the state in which a system remains for a long period of time, and any slight disturbance causing the system to deviate from the metastable state does not result in the system passing into another state.
As soon as the external disturbance is removed, the system will return into the initial metastable state Tschoegl, A sufficiently strong disturbance, however, will put the system out of the metastable state, and the system will pass into a new state of stable equilibrium Tschoegl, Metastability and its application to human movement: For the individual, minor challenges of balance can be easily compensated for by conscious and unconscious motor control mechanisms.
The mover will perceive his state of motion to be stable while his state of equilibrium is in fact metastable. For large challenges of balance, the mover may perceive his state of motion to be unstable while periodically approaching unstable states of equilibrium.
Again, running is a good example of human locomotor metastability as the individual moves from a relative stable state stance phase by a muscular disturbance or perturbation push-off phase to achieve a new state of equilibrium subsequent stance-phase. With locomotion, there are constant fluctuations in CoM relative to the BoS, which demand metastable control Figure 1. While metastability is considered to be a core feature of dynamic systems den Hollander, , the metastability concept should be applied to the issue of balance performance as well since the human body can be envisioned as a dynamic system with its response behavior following internal breathing and external tackling during ball games perturbations.
In conclusion and in accordance with Kibele et al.
[PDF] Germany Beyond the Stable State
National Center for Biotechnology Information , U. J Sports Sci Med. Received Sep 7; Accepted Sep At the moment, my stable state is life after the kids have all left home and finished college—but how stable unchanging will it actually turn out to be?
Schon takes it as a given that things will never settle down. The appropriate response to any change, in his view, is to understand it, not to fight it or even to surrender to it: Nor is it that easy to read—the passage above is contrasted by more than a few stretches of fuzzy prose: Constant reorienting is a crucial skill, as is that of not being too afraid to make mistakes one can learn from.
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In a more condensed and perhaps more accessible format, this could well be an essential text that should be passed out and taught to high schoolers already forming the illusion that things will settle down once they finish college and get a job. Beyond the Stable State, by Donald A.
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I appreciate your throwing these in the mix. I can promise you that I will check it out at the local university library. Or anything by Martin Mayer. Having read The Lawyers and then entered law school, it amazes me how relevant much of what he said in the late s remains accurate about the profession today.
And it is most certainly out of print and neglected. Again, thanks for your work here — fiction or nonfiction, one of the best sites on the web. Both books were enormously useful—primers, really, on how the banking system works and the forces that drive its development. Well, like they always say, change is inevitable. Change will always be constant.