WordNet

(psychology) a state of mental or emotional strain or suspense; "he suffered from fatigue and emotional tension"; "stress is a vasoconstrictor" (同)tenseness, stress
the physical condition of being stretched or strained; "it places great tension on the leg muscles"; "he could feel the tenseness of her body" (同)tensity, tenseness, tautness
(physics) a stress that produces an elongation of an elastic physical body; "the direction of maximum tension moves asymptotically toward the direction of the shear"
a balance between and interplay of opposing elements or tendencies (especially in art or literature); "there is a tension created between narrative time and movie time"; "there is a tension between these approaches to understanding history"
the action of stretching something tight; "tension holds the belt in the pulleys"
make ones way by force; "He muscled his way into the office"
animal tissue consisting predominantly of contractile cells (同)muscular_tissue
one of the contractile organs of the body (同)musculus
authority or power or force (especially when used in a coercive way); "the senators used their muscle to get the party leader to resign"

PrepTutorEJDIC

〈U〉『ぴんと張ること』,伸長;ぴんと張った状態,張り / 〈U〉(精神的・感情的)『緊張』 / 〈C〉《複数形で》(一般に)『緊張状態(関係)』 / 〈U〉張力,引っ張る力 / 〈U〉起電力;電圧(voltage)
〈U〉(動物体の組織としての)『筋肉』,筋(きん);〈C〉(体の各部を動かす)筋肉 / 〈U〉力,(特に)筋力,腕力 / 《俗に》(…に)強引に割り込む《+『in on』(『into, through』)+『名』》
筋肉の,筋力のある / 力ずくの

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/06/26 07:47:17」(JST)

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In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state.^[1] It helps to maintain posture and declines during REM sleep.^{[citation needed]}

Purpose

If a sudden pull or stretch occurs, the body responds by automatically increasing the muscle's tension, a reflex which helps guard against danger as well as helping to maintain balance. Such near-continuous innervation can be thought of as a "default" or "steady state" condition for muscles. There is, for the most part, no zero-activity resting state insofar as activation is concerned. In other words, rest is a state of low activity but not zero activity. Both the extensor and flexor muscles are involved in the maintenance of a constant tone while at rest. In skeletal muscles, this helps maintain a normal posture.

Resting muscle tone varies along a bell shaped curve. Low tone is experienced as "floppy, mushy, dead weight" and high tone is experienced as "light, tight, and strong". Muscles with high tone are not necessarily strong and muscles with low tone are not necessarily weak. In general, low tone does increase flexibility and decrease strength and high tone does decrease flexibility and increase strength, but with many exceptions. A person with low tone will most likely not be able to engage in "explosive" movement such as needed in a sprinter or high jumper. These athletes usually have high tone that is within normal limits. A person with high tone will usually not be flexible in activities such as dance and yoga. Joint laxity contributes greatly to flexibility, especially with flexibility in one or a few areas, instead of overall flexibility.

For example, a person can be high tone with normal to poor flexibility in most areas, but be able to put the palms of the hands on the floor with straight knees due to hypermobile sacroiliac joints. It is important to assess several areas before deciding if a person has high, low or normal muscle tone. A fairly reliable assessment item is how the person feels when picked up. For example, small children with low tone can feel heavy while larger, high tone children feel light, which corresponds with the description of "dead weight".

Although cardiac muscle and smooth muscle are not directly connected to the skeleton, they also have tonus in the sense that although their contractions are not matched with those of antagonist muscles, the non-contractile state is characterized by (sometimes random) enervation.

Pathological tonus

Physical disorders can result in abnormally low (hypotonia) or high (hypertonia) muscle tone. Another form of hypertonia is paratonia, which is associated with dementia. Hypotonia is seen in lower motor neuron disease like poliomyelitis. Hypotonia can present clinically as muscle flaccidity, where the limbs appear floppy, stretch reflex responses are decreased, and the limb's resistance to passive movement is also decreased.^[1] Hypertonia is seen in upper motor neuron diseases like lesions in pyramidal tract and extrapyramidal tract. Hypertonia can present clinically as either spasticity or rigidity. While spasticity is velocity-dependent resistance to passive stretch (i.e. passively moving an elbow quickly will elicit increased muscle tone, but passively moving elbow slowly may not elicit increased muscle tone), rigidity is velocity-independent resistance to passive stretch (i.e. there is uniform increased tone whether the elbow is passively moved quickly or slowly).^[1] Spasticity can be in the form of the clasp-knife response, in which there is increased resistance only at the beginning or at the end of the movement. Rigidity can be of the leadpipe type, in which there is resistance throughout to passive movement, or it may be of cogwheel type, in which the resistance to passive movement is in a jerky manner.

Tonus in surgery

In ophthalmology, tonus may be a central consideration in eye surgery, as in the manipulation of extraocular muscles to repair strabismus. Tonicity aberrations are associated with many diseases of the eye (e.g. Adie syndrome).

Cramps

Normally, people are unaware of their muscle tone in their daily activities. The body maintains the balance between the tone of flexor and extensor muscle groups. Sometimes, in normal, healthy people, that tone is lost either in flexors or extensor muscle groups in isolation, temporarily and intermittently resulting in "muscle cramps". Treating these extensor or flexor group of muscles in isolation to relax can be difficult. Generally, muscle relaxants or quinine can help with cramps and is warranted when they become troublesome. But these medication cause their relaxing effect in both groups by moderating their tone. The cause of disproportionate intermittent contractions of either flexors or extensors or the cause of cramps is unknown. The stimulus for these "cramps" may originate in the cerebral cortex, the spinal cord, or the muscle itself. This could indicate developing pathology or other problems in the future.

References

^ ^a ^b ^c O’Sullivan, S. B. (2007). Examination of motor function: Motor control and motor learning. In S. B. O’Sullivan, & T. J. Schmitz (Eds), Physical rehabilitation (5th ed.) (pp. 233-234). Philadelphia, Pennsylvania: F. A. Davis Company.

External links

BBC series on muscles

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