Standing

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Standing women

Standing, also referred to as orthostasis, is a position in which the body is held in an upright (orthostatic) position and supported only by the feet. Although seemingly static, the body rocks slightly back and forth from the ankle in the sagittal plane, which bisects the body into right and left sides. The sway of quiet standing is often likened to the motion of an inverted pendulum. [1]

Contents

Standing at attention is a military standing posture, as is stand at ease, but these terms are also used in military-style organisations and in some professions which involve standing, such as modeling. At ease refers to the classic military position of standing with legs slightly apart, not in as formal or regimented a pose as standing at attention. In modeling, model at ease refers to the model standing with one leg straight, with the majority of the weight on it, and the other leg tucked over and slightly around. There may be a time when a person is standing, where they lose control due to an external force or lack of energy, where they accelerate to the ground due to gravity. This is known as "falling" and may result in injuries around the part of the body that made contact with the ground.

Control

Standing posture relies on dynamic rather than static balance. The human center of mass is in front of the ankle, and unlike in quadrupeds, the base of support is narrow, consisting of only two feet. A static pose would cause humans to fall forward onto the face. [2] 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. Humans begin to stand between 8 and 12 months of age.

A child learning to stand Child Learning to Stand.png
A child learning to stand

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. 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. [3] [4]

Nervous system

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. [5] [6]

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. [7]

Core muscles

The core muscles play a role in maintaining stability. The core muscles are deep muscle layers that lie 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. [8] [9]

Expansion of pendulum model

Some investigators have replaced the ankle inverted pendulum analogy with a model of double linked pendulums involving both hip and ankle sway. [10] Neither model is accepted as more than an approximation. Analysis of postural sway shows much more variation than is seen in a physical pendulum or even a pair of coupled pendulums. Furthermore, quiet standing involves activity in all joints, not just the ankles or hips. [11]

In the past, the variation was attributed to random effects. [12] A more recent interpretation is that sway has a fractal structure. [13] [14] [15] 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. [16] In other words, the body cannot compensate well enough for imbalances.

Pathology

Although standing per se is not 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 is characterized by 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 does not 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 advisories. Many of them, however, are specific for a certain cause of orthostatic hypotension, e.g. maintaining a proper fluid intake in dehydration.

Orthostatic hypercoagulability

Prolonged still standing significantly activates the coagulation cascade, called orthostatic hypercoagulability. Overall, it causes an increase in transcapillary hydrostatic pressure. As a result, approximately 12% of blood plasma volume crosses into the extravascular compartment. This plasma shift causes an increase in the concentration of coagulation factors and other proteins of coagulation, in turn causing hypercoagulability. [17]

Orthostatic tremor

Characterized by fast (12–18 Hz) rhythmic muscle contractions that occur in the legs and trunk immediately after standing. No other clinical signs or symptoms are present and the shaking ceases when the patient sits or is lifted off the ground. The high frequency of the tremor often creates a rippling effect on the leg muscles while standing.

Long-term complications

Standing per se does not pose any harm. In the long term, however, complications may arise.

See also

Related Research Articles

Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure drops when they are standing up (orthostasis) or sitting down. Primary orthostatic hypotension is also often referred to as neurogenic orthostatic hypotension. The drop in blood pressure may be sudden, within 3 minutes or gradual. It is defined as a fall in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg after 3 minutes of standing. It occurs predominantly by delayed constriction of the lower body blood vessels, which is normally required to maintain adequate blood pressure when changing the position to standing. As a result, blood pools in the blood vessels of the legs for a longer period, and less is returned to the heart, thereby leading to a reduced cardiac output and inadequate blood flow to the brain.

<span class="mw-page-title-main">Hypotension</span> Abnormally low blood pressure

Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is indicated by two numbers, the systolic blood pressure and the diastolic blood pressure, which are the maximum and minimum blood pressures within the cardiac cycle, respectively. A systolic blood pressure of less than 90 millimeters of mercury (mmHg) or diastolic of less than 60 mmHg is generally considered to be hypotension. Different numbers apply to children. However, in practice, blood pressure is considered too low only if noticeable symptoms are present.

<span class="mw-page-title-main">Muscle spindle</span> Innervated muscle structure involved in reflex actions and proprioception

Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be processed by the brain as proprioception. The responses of muscle spindles to changes in length also play an important role in regulating the contraction of muscles, for example, by activating motor neurons via the stretch reflex to resist muscle stretch.

<span class="mw-page-title-main">Skeletal muscle pump</span> Muscular system aiding blood circulation

The skeletal muscle pump or musculovenous pump is a collection of skeletal muscles that aid the heart in the circulation of blood. It is especially important in increasing venous return to the heart, but may also play a role in arterial blood flow.

Orthostatic intolerance (OI) is the development of symptoms when standing upright that are relieved when reclining. There are many types of orthostatic intolerance. OI can be a subcategory of dysautonomia, a disorder of the autonomic nervous system occurring when an individual stands up. Some animal species with orthostatic hypotension have evolved to cope with orthostatic disturbances.

<span class="mw-page-title-main">Postural orthostatic tachycardia syndrome</span> Abnormally high heart rate after a postural change

Postural orthostatic tachycardia syndrome (POTS) is a condition characterized by an abnormally large increase in heart rate upon sitting up or standing. POTS is a disorder of the autonomic nervous system that can lead to a variety of symptoms, including lightheadedness, brain fog, blurred vision, weakness, fatigue, headaches, heart palpitations, exercise intolerance, nausea, diminished concentration, tremulousness (shaking), syncope (fainting), coldness or pain in the extremities, numbness or tingling in the extremities, chest pain, and shortness of breath. Other conditions associated with POTS include myalgic encephalomyelitis/chronic fatigue syndrome, migraine headaches, Ehlers–Danlos syndrome, asthma, autoimmune disease, vasovagal syncope, and mast cell activation syndrome. POTS symptoms may be treated with lifestyle changes such as increasing fluid, electrolyte, and salt intake, wearing compression stockings, gentle and slow postural changes, avoiding prolonged bedrest, medication, and physical therapy.

Astasis is a lack of motor coordination marked by an inability to stand, walk or even sit without assistance due to disruption of muscle coordination.

<span class="mw-page-title-main">Sinus tachycardia</span> Sinus rhythm with a rate that is higher than normal

Sinus tachycardia is a sinus rhythm of the heart, with an increased rate of electrical discharge from the sinoatrial node, resulting in a tachycardia, a heart rate that is higher than the upper limit of normal.

<span class="mw-page-title-main">Soleus muscle</span> Muscle in the back part of the lower leg

In humans and some other mammals, the soleus is a powerful muscle in the back part of the lower leg. It runs from just below the knee to the heel and is involved in standing and walking. It is closely connected to the gastrocnemius muscle, and some anatomists consider this combination to be a single muscle, the triceps surae. Its name is derived from the Latin word "solea", meaning "sandal".

<span class="mw-page-title-main">Tilt table test</span> Medical procedure often used to diagnose dysautonomia or syncope

A tilt table test (TTT), occasionally called upright tilt testing (UTT), is a medical procedure often used to diagnose dysautonomia or syncope. Patients with symptoms of dizziness or lightheadedness, with or without a loss of consciousness (fainting), suspected to be associated with a drop in blood pressure or positional tachycardia are good candidates for this test.

<span class="mw-page-title-main">Pure autonomic failure</span> Medical condition

Pure autonomic failure (PAF) is an uncommon, sporadic neurodegenerative condition marked by a steadily declining autonomic regulation. Bradbury and Eggleston originally described pure autonomic failure in 1925.

<span class="mw-page-title-main">Interstitial cell of Cajal</span>

Interstitial cells of Cajal (ICC) are interstitial cells found in the gastrointestinal tract. There are different types of ICC with different functions. ICC and another type of interstitial cell, known as platelet-derived growth factor receptor alpha (PDGFRα) cells, are electrically coupled to smooth muscle cells via gap junctions, that work together as an SIP functional syncytium. Myenteric interstitial cells of Cajal (ICC-MY) serve as pacemaker cells that generate the bioelectrical events known as slow waves. Slow waves conduct to smooth muscle cells and cause phasic contractions.

The complications of prolonged standing are conditions that may arise after standing, walking, or running for prolonged periods. Many of the complications come from prolonged standing that is repeated several times a week. Many jobs require prolonged standing, such as "retail staff, baristas, bartenders, assembly line workers, security staff, engineers, catering staff, library assistants, hair stylists and laboratory technicians". The basic physiological change that occurs in the body during prolonged standing or sudden stand from supine position is that there will be increased pooling of blood in the legs. This decreases the venous return, and so there will be decreased cardiac output, which ultimately causes systolic blood pressure to fall (hypotension). This hypotension may lead the subject to faint or to have other symptoms of hypotension. Standing requires about 10% more energy than sitting.

<span class="mw-page-title-main">Balance (ability)</span> Ability to maintain the line of gravity of a body

Balance in biomechanics, is an ability to maintain the line of gravity of a body within the base of support with minimal postural sway. Sway is the horizontal movement of the centre of gravity even when a person is standing still. A certain amount of sway is essential and inevitable due to small perturbations within the body or from external triggers. An increase in sway is not necessarily an indicator of dysfunctional balance so much as it is an indicator of decreased sensorimotor control.

<span class="mw-page-title-main">Dopamine beta hydroxylase deficiency</span> Medical condition

Dopamine beta (β)-hydroxylase deficiency is a human medical condition involving inadequate dopamine beta-hydroxylase. It is characterized by increased amounts of serum dopamine and the absence of norepinephrine (NE) and epinephrine.

<span class="mw-page-title-main">Proprioception</span> Sense of self-movement, force, and body position

Proprioception is the sense of self-movement, force, and body position.

Orthostatic syncope refers to syncope resulting from a postural decrease in blood pressure, termed orthostatic hypotension.

<span class="mw-page-title-main">Neuromechanics</span> Interdisciplinary field

Neuromechanics is an interdisciplinary field that combines biomechanics and neuroscience to understand how the nervous system interacts with the skeletal and muscular systems to enable animals to move. In a motor task, like reaching for an object, neural commands are sent to motor neurons to activate a set of muscles, called muscle synergies. Given which muscles are activated and how they are connected to the skeleton, there will be a corresponding and specific movement of the body. In addition to participating in reflexes, neuromechanical process may also be shaped through motor adaptation and learning.

<span class="mw-page-title-main">Gait deviations</span> Medical condition

Gait deviations are nominally referred to as any variation of standard human gait, typically manifesting as a coping mechanism in response to an anatomical impairment. Lower-limb amputees are unable to maintain the characteristic walking patterns of an able-bodied individual due to the removal of some portion of the impaired leg. Without the anatomical structure and neuromechanical control of the removed leg segment, amputees must use alternative compensatory strategies to walk efficiently. Prosthetic limbs provide support to the user and more advanced models attempt to mimic the function of the missing anatomy, including biomechanically controlled ankle and knee joints. However, amputees still display quantifiable differences in many measures of ambulation when compared to able-bodied individuals. Several common observations are whole-body movements, slower and wider steps, shorter strides, and increased sway.

References

  1. ↑ Gage WH, Winter DA, Frank JS, Adkin AL (April 2004). "Kinematic and kinetic validity of the inverted pendulum model in quiet standing". Gait & Posture. 19 (2): 124–32. doi:10.1016/S0966-6362(03)00037-7. PMID   15013500.
  2. ↑ Loram ID, Maganaris CN, Lakie M (May 2004). "Paradoxical muscle movement in human standing". J. Physiol. 556 (Pt 3): 683–9. doi:10.1113/jphysiol.2004.062398. PMC   1664994 . PMID   15047776.
  3. ↑ Loram ID, Maganaris CN, Lakie M (May 2004). "Paradoxical muscle movement in human standing". J. Physiol. 556 (Pt 3): 683–9. doi:10.1113/jphysiol.2004.062398. PMC   1664994 . PMID   15047776.
  4. ↑ Loram ID, Maganaris CN, Lakie M (April 2005). "Human postural sway results from frequent, ballistic bias impulses by soleus and gastrocnemius". J. Physiol. 564 (Pt 1): 295–311. doi:10.1113/jphysiol.2004.076307. PMC   1456055 . PMID   15661824.
  5. ↑ Hodges PW, Gurfinkel VS, Brumagne S, Smith TC, Cordo PC (June 2002). "Coexistence of stability and mobility in postural control: evidence from postural compensation for respiration". Exp Brain Res. 144 (3): 293–302. doi:10.1007/s00221-002-1040-x. PMID   12021811. S2CID   2821680.
  6. ↑ Loram ID, Lakie M (December 2002). "Direct measurement of human ankle stiffness during quiet standing: the intrinsic mechanical stiffness is insufficient for stability". J. Physiol. 545 (Pt 3): 1041–53. doi:10.1113/jphysiol.2002.025049. PMC   2290720 . PMID   12482906.
  7. ↑ Standing, Line of Gravity at Joints, Postural Sway and Correction of Perturbations
  8. ↑ Lee SW, Chan CK, Lam TS, et al. (September 2006). "Relationship between low back pain and lumbar multifidus size at different postures". Spine. 31 (19): 2258–62. doi:10.1097/01.brs.0000232807.76033.33. PMID   16946664. S2CID   12317657.
  9. ↑ Hides JA, Stokes MJ, Saide M, Jull GA, Cooper DH (January 1994). "Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain". Spine. 19 (2): 165–72. doi: 10.1097/00007632-199401001-00009 . PMID   8153825.
  10. ↑ Sasagawa, S; Ushiyama, J; Kouzaki, M; Kanehisa, H (2009). "Effect of the hip motion on the body kinematics in the sagittal plane during human quiet standing". Neuroscience Letters. 450 (1): 27–31. doi:10.1016/j.neulet.2008.11.027. PMID   19027828. S2CID   46052026.
  11. ↑ Wu, Jianhua; McKay, Sandra; Angulo-Barroso, Rosa (2009). "Center of mass control and multi-segment coordination in children during quiet stance". Experimental Brain Research. 196 (3): 329–39. doi:10.1007/s00221-009-1852-z. PMID   19484228. S2CID   7613612.
  12. ↑ Collins JJ, De Luca CJ (August 1994). "Random walking during quiet standing". Phys. Rev. Lett. 73 (5): 764–7. Bibcode:1994PhRvL..73..764C. doi:10.1103/PhysRevLett.73.764. PMID   10057531.
  13. ↑ Doyle TL, Dugan EL, Humphries B, Newton RU (2004). "Discriminating between elderly and young using a fractal dimension analysis of centre of pressure". Int J Med Sci. 1 (1): 11–20. doi:10.7150/ijms.1.11. PMC   1074506 . PMID   15912186.
  14. ↑ Borg, Frank G. Random Walk and Balancing. arxiv.org
  15. ↑ Yamada, Norimasa (1995). "Chaotic swaying of the upright posture". Human Movement Science. 14 (6): 711–726. doi:10.1016/0167-9457(95)00032-1.
  16. ↑ Blaszczyk, Janusz W.; Bacik, Bogdan; Juras, Grzegorz (2003). "Clinical Assessment of Postural Stability". Journal of Mechanics in Medicine and Biology . 03 (2): 135. doi:10.1142/S0219519403000715.
  17. ↑ Masoud M, Sarig G, Brenner B, Jacob G (June 2008). "Orthostatic hypercoagulability: a novel physiological mechanism to activate the coagulation system". Hypertension. 51 (6): 1545–51. doi: 10.1161/HYPERTENSIONAHA.108.112003 . PMID   18413485.
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