Human position

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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.


Contents

[edit] Basic human positions

While not moving, a human can be in one of the following main positions.

[edit] 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. Our Center of Mass (COM) is in front of the ankle. Unlike tetrapods our base of support is narrow, consisting of only two feet and a static pose would cause us to keel over on our face. In addition, we are constantly subjected to external perturbations such as breeze and internal perturbations from respiration. Erect posture requires adjustment and correction. Traditionally our correction was explained by the spring action of our muscles. This is a local mechanism that takes place without the intervention of the Central Nervous System (CNS). Recent studies, however, show that 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 CNS continually monitors our direction and velocity below our conscious awareness. Our vertical body axis alternates between forward and backwards tilts. Before each tilt reaches the tipover point the CNS 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 is volleyed back and forth between two players and is not allowed to touch the ground. The muscle exertion required to maintain an aligned standing posture is crucial but minimal. A little goes a long way. Electromyography has detected slight activity in the muscles of the calves, hips and lower back. [6]

Although the pendulum model is a good approximation, a time series 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 mucles has been implicated in back pain.[11] [12]

[edit] Kneeling

On one or both knees, shin(s) approximately parallel to the ground (possibly raised to an angle depending on the position of the feet), torso usually upright but can be considered kneeling at other angles not touching the ground.

[edit] Sitting

Sitting requires a more or less horizontal structure, e.g. 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 go horizontally underneath the thigh in a seiza.

[edit] Supine

Lying horizontal, face up. Toes up

[edit] Prone

Lying horizontally, facing down.

[edit] Lying on the side

Lying on either side, straight, curled concave or curled convex.

[edit] Fetal position

[edit] 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 various 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.

These stable postures attained over time is a result of one's lifestyle and orientation. Over time people come to attain an average posture, bad or inefficient posture, and sometimes a good or effective posture. 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 posture or slouching posture is unable to optimally distribute weight across the body framework, and hence is ineffective. An average posture is able to maintain distribution of weight and form but does not attain optimal form and maintenance. A good posture or an 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 posture 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 (horizontal spar on the mast of a ship). Hence 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 gets ready 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.

[edit] 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, the consequence often being what is termed a military posture 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 also famed for their posture, which is a product of their natural lifestyle. Their beauty was documented by the Motion Picture director Leni Riefenstahl. Across societies, various stylizations of human positions and postures are set for specific occasions, which include etiquette and ceremonial conducts.

[edit] See also

[edit] References

  1. ^ 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
  2. ^ http://jp.physoc.org/cgi/content/full/556/3/683 Paradoxical muscle movement in human standing
  3. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1456055 Human postural sway results from frequent, ballistic bias impulses by soleus and gastrocnemius
  4. ^ http://www.springerlink.com/content/3ehpvwx0k4231rcv/ Coexistence of stability and mobility in postural control: evidence from postural compensation for respiration
  5. ^ 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
  6. ^ 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
  7. ^ http://prola.aps.org/abstract/PRL/v73/i5/p764_1 Random Walking during Quiet Standing
  8. ^ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1074506 Discriminating between elderly and young using a fractal dimension analysis of centre of pressure
  9. ^ http://arxiv.org/pdf/physics/0411138 Random Walk and Balancing
  10. ^ http://utopia.duth.gr/~pmarhav/12th-ICMMB/PDF12thConference/12-Blaszczyk.pdf CLINICAL ASSESSMENT OF POSTURAL STABILITY
  11. ^ 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.
  12. ^ 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.

[edit] External links

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