WordNet

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〉(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』》
(重量単位の)『トン』 / (容積単位の)トン(物によって異なり,木材では40立方フィート,小麦では20立方フィート) / 《話》大量(の…),多数(の…)《+of+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）』「2016/08/29 20:34:14」(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

Muscle Tone, a Hot Wheels model

UpToDate Contents

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1. 筋力低下の評価における筋力検査 muscle examination in the evaluation of weakness
2. 筋力低下患者へのアプローチ approach to the patient with muscle weakness
3. 慢性閉塞性肺疾患（COPD）における呼吸筋のトレーニングおよび安静 respiratory muscle training and resting in copd
4. 救急外来における急性の筋力低下を訴える成人の評価 evaluation of the adult with acute weakness in the emergency department
5. 糖尿病性筋梗塞 diabetic muscle infarction

English Journal

In vivo single-molecule imaging identifies altered dynamics of calcium channels in dystrophin-mutant C. elegans.

Zhan H1, Stanciauskas R2, Stigloher C3, Dizon KK2, Jospin M1, Bessereau JL1, Pinaud F4.
Nature communications.Nat Commun.2014 Sep 18;5:4974. doi: 10.1038/ncomms5974.
Single-molecule (SM) fluorescence microscopy allows the imaging of biomolecules in cultured cells with a precision of a few nanometres but has yet to be implemented in living adult animals. Here we used split-GFP (green fluorescent protein) fusions and complementation-activated light microscopy (CAL
PMID 25232639

Skeletal muscle fibrosis and stiffness increase after rotator cuff tendon injury and neuromuscular compromise in a rat model.

Sato EJ1, Killian ML, Choi AJ, Lin E, Esparza MC, Galatz LM, Thomopoulos S, Ward SR.
Journal of orthopaedic research : official publication of the Orthopaedic Research Society.J Orthop Res.2014 Sep;32(9):1111-6. doi: 10.1002/jor.22646. Epub 2014 May 19.
Rotator cuff tears can cause irreversible changes (e.g., fibrosis) to the structure and function of the injured muscle(s). Fibrosis leads to increased muscle stiffness resulting in increased tension at the rotator cuff repair site. This tension influences repairability and healing potential in the c
PMID 24838823

Pericyte Contractility Controls Endothelial Cell Cycle Progression and Sprouting: Insights into Angiogenic Switch Mechanics.

Durham JT1, Surks HK1, Dulmovits BM1, Herman IM2.
American journal of physiology. Cell physiology.Am J Physiol Cell Physiol.2014 Aug 20. pii: ajpcell.00185.2014. [Epub ahead of print]
Microvascular stability and regulation of capillary tonus is regulated by pericytes and their interactions with endothelial cells. While the RhoA/Rho Kinase (ROCK) pathway has been implicated in modulating pericyte contractility, in part via regulation of the myosin light chain phosphatase (MLCP), t
PMID 25143350

Japanese Journal

Relaxing Effect of Acupuncture Stimulation on Hypertonic Muscle in a Rat Model

INOUE Motohiro,NAKAJIMA Miwa,ITOI Megumi
日本温泉気候物理医学会雑誌 78(3), 187-194, 2015
… Background: The relaxing phenomenon induced by acupuncture on hypertonic muscle has not clearly been demonstrated. … We studied whether acupuncture stimulation on the hypertonic muscle model induce relaxation. … Group treated with acupuncture stimulation of the triceps surae muscle (N = 9). …
NAID 130005072051

脳性麻痺の脊柱側弯変形に対する動的脊柱装具の介護者からみた効果の検討

吉田清志,鈴木恒彦,松井吉裕 [他],樋口周久,梶浦一郎
The Japanese Journal of Rehabilitation Medicine 52(4-5), 251-255, 2015
目的：脳性麻痺患者における脊柱側弯変形は日常生活動作に著しい障害をもたらす．我々は独自に開発した動的脊柱装具（Dynamic Spinal Brace：DSB）を用いた脊柱側弯変形に対する治療の有効性を患者，介護者の状況の変化において検討した．方法：DSB治療中の脳性麻痺患者222 人を対象に，介護者へのアンケート調査および側弯変形のX線計測を行った．結果：アンケートでは日常生活動作において座位・ …
NAID 130005068618