Standing (position)
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Standing is a human position in which the body constantly is in an orthostatic state.
Although quiet standing appears to be static, modern instrumentation shows it to be a process of rocking from the ankle in the sagittal plane. The sway of quiet standing is often likened to the motion of an inverted pendulum. [1]
Contents |
Control
Standing posture relies on dynamic rather than static balance. The human center of mass is in front of the ankle, and unlike tetrapods, the base of support is narrow, consisting of only two feet. A static pose would cause humans to fall forward onto the face. In addition, there are constant external perturbations, such as breezes, and internal perturbations that come from respiration. Erect posture requires adjustment and correction. There are many mechanisms in the body that are suggested to control this, e.g. a spring action in muscles, higher control from the nervous system or core muscles.
Spring action
Traditionally, such correction was explained by the spring action of the muscles, a local mechanism taking place without the intervention of the central nervous system (CNS). Recent studies, however, show that this spring action by itself is insufficient to prevent a forward fall. Also, human sway is too complicated to be adequately explained by spring action. [2][3]
Nervous system
According to current theory, however, the nervous system continually and unconsciously monitors our direction and velocity. The vertical body axis alternates between tilting forward and backward. Before each tilt reaches the tipover point the nervous system counters with a signal to reverse direction. Sway also occurs in the hip and there is a slight winding and unwinding of the lower back. [4][5]
An analogy would be a ball that volleys back and forth between two players without touching the ground. The muscle exertion required to maintain an aligned standing posture is crucial but minimal. Electromyography has detected slight activity in the muscles of the calves, hips and lower back. [6]
Core muscles
Lately, attention has focused on the role of the core muscles in maintaining stability. The core muscles are deep muscle layers that lay close to the spine and provide structural support. The transverse abdominals wrap around the spine and function as a compression corset. The multifidi are intersegmental muscles. Dysfunction in the core muscles has been implicated in back pain.[7][8]
Expansion of pendulum model
Although the pendulum model is a good approximation, analysis of postural sway shows much more variation than is seen in a physical pendulum. In the past the variation was attributed to random effects[9]. A more recent interpretation is that sway has a fractal structure[10][11]. A fractal pattern consists of a motif repeated at varying levels of magnification. The levels are related by a ratio called the fractal dimension. It is believed that the fractal pattern offers a range of fine and gross control tuning. Fractal dimension is altered in some motor dysfunctions[12]. In other words, the body cannot compensate well enough for imbalances.
Pathology
Although standing per se isn't dangerous, there are pathologies associated with it. One short term condition is orthostatic hypotension, and long term conditions are sore feet, stiff legs and low back pain.
Orthostatic hypotension
Orthostatic hypotension means an unusually low blood pressure when the patient is standing up.
It can cause dizziness, lightheadedness, headache, blurred or dimmed vision and fainting, because the brain doesn't get sufficient blood supply. This, in turn, is caused by gravity, pulling the blood into the lower part of the body.
Normally, the body compensates, but in the presence of other factors, e.g. hypovolemia, diseases and medications, this response may not be sufficient.
There are medications to treat hypotension. In addition, there are many lifestyle advices. Many of them, however, are specific for a certain cause of orthostatic hypotension, e.g. maintaining a proper fluid intake in dehydration.
Long-term complications
Standing per se doesn't pose any harm. In the long term, however, complications may arise.
Optimal and balanced erect posture
Posture is the emergent alignment of the body that remains relatively constant in its underlying structure and unity across many forms of human positions. It refers to the unconscious and stable structural disposition of the body framework attained over a long period of continuous body movements and patterns.
Postures are attained over time as a result of lifestyle and orientation. Good or bad posture are results of habitual ways of holding the body. The quality or effectiveness of posture is related to the proportionate structure of the body framework and the optimal balance of the body.
A bad or slouching posture is unable to optimally distribute weight across the body framework, and is hence ineffective. An average posture is able to maintain distribution of weight and form but does not attain optimal form and maintenance. A good or erect posture is able to completely and optimally attain balance and proportion of the body mass and framework. A well proportioned erect posture optimizes breathing and affects the circulation of bodily fluids. An erect posture is therefore most desirable and highly effective for the body structure and proportion.
An erect or well-proportioned posture involves various elements of the body and its co-ordination. It includes optimally unfurling the spine until the lower back curves inside while holding the chest raised high without straining breathing. The head assumes an optimal position while keeping the chin parallel to the ground. In an erect posture, the shoulders are very straight and pulled back. This acts like the yardarm (the horizontal spar on the mast of a ship). While bending, even though the spine would curve, the posture still remains erect because the shoulders remain straight and pulled back maintaining the body proportion and balance. The optimal structural alignment of the body leads to a back that is straight and symmetric in the coronal plane. In the sagittal plane a normal back has a slight S curve. This structural alignment consolidates over a long span of time leading to a well balanced posture that becomes a natural disposition.
In posturology, posture is elaboration and active preservation of the configuration of the various segments of the body in the space; it expresses the way body faces the stimulation of the outside world and prepares to react to it.
The configuration of the various segments of the body in space is elaborated on a mode rather phasic but not exclusively, it is maintained on a rather tonic mode but not exclusively.
A well balanced or erect posture is considered as an integral part of physical attractiveness. In most cultures an erect posture is considered as a mark of a well balanced and adaptable personality.
Military regimentation and several boarding schools enforce regimen on young people to have an erect posture. Often, though results what is termed a military or over-correct posture which may be considered excessively erect with poor balance resulting from excessive tension in the back muscles. Other communities stress posture as an integral part of their lifestyle. The Nuba people in Africa are famed for their posture, which is a product of their natural lifestyle. Their beauty was documented by film director Leni Riefenstahl.[3]
External links
References
- ↑ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15013500&dopt=Abstract Kinematic and kinetic validity of the inverted pendulum model in quiet standing
- ↑ http://jp.physoc.org/cgi/content/full/556/3/683 Paradoxical muscle movement in human standing
- ↑ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1456055 Human postural sway results from frequent, ballistic bias impulses by soleus and gastrocnemius
- ↑ http://www.springerlink.com/content/3ehpvwx0k4231rcv/ Coexistence of stability and mobility in postural control: evidence from postural compensation for respiration
- ↑ http://jp.physoc.org/cgi/content/abstract/545/3/1041 Direct measurement of human ankle stiffness during quiet standing: the intrinsic mechanical stiffness is insufficient for stability
- ↑ http://medicalsciences.med.unsw.edu.au/SOMSWeb.nsf/resources/ANAT314104/$file/FA2-16-POSTURE1-stance.pdf Standing, Line of Gravity at Joints, Postural Sway and Correction of Perturbations
- ↑ [1] Relationship between low back pain and lumbar multifidus size at different postures.
- ↑ [2] Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain.
- ↑ http://prola.aps.org/abstract/PRL/v73/i5/p764_1 Random Walking during Quiet Standing
- ↑ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1074506 Discriminating between elderly and young using a fractal dimension analysis of centre of pressure
- ↑ http://arxiv.org/pdf/physics/0411138 Random Walk and Balancing
- ↑ http://utopia.duth.gr/~pmarhav/12th-ICMMB/PDF12thConference/12-Blaszczyk.pdf CLINICAL ASSESSMENT OF POSTURAL STABILITY
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
