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Human position refers to a position of a human body. It can also be called a person's attitude or bearing.
Basic human positions
While not moving, a human can be in one of the following main positions.
Standing
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]
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. 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]
According to current theory, 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]
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[7]. A more recent interpretation is that sway has a fractal structure[8][9]. 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[10].
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.[11][12]
Kneeling
Kneeling is standing not on the feet, but on one or both knees or shins approximately parallel to the ground, possibly raised to an angle depending on the position of the feet. The torso is usually upright but can be considered kneeling at other angles not touching the ground.
Sitting
Sitting requires a more or less horizontal structure, like a chair or the ground. Special ways of sitting are with the legs horizontal, and in an inclined seat. While on a chair the shins are usually vertical, on the ground the shins may be crossed in the lotus position or be placed horizontally under the thigh in a seiza.
Supine
Lying on the back with the face up.
Lying (or laying) on the chest with the face down ("lying down", "laying down", or "going prone").
Lying on the side
Lying on either side, with the body straight, or concavely or convexly curled.
Lying or sitting with the head close to the knees.
Optimal human positions 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.
Human positions and posture in society
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.
Young boys and men are expected to have erect postures. 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. Across societies, various stylizations of human positions and postures are used in specific occasions, particually ceremonies.
See also
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
- ^ 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
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16946664&query_hl=1&itool=pubmed_docsum Relationship between low back pain and lumbar multifidus size at different postures.
- ^ http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=8153825&query_hl=15&itool=pubmed_docsum Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain.