Talk:Skeletal muscle

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Skeletal (Striated) Muscle[edit]

Do all mammals have the same form of striated muscle fibre? I expect the metabolism is the same but what about other groups? Derek H

All mammals have the basic "fast" and "slow" muscle fiber types, denoted by different isoforms of Myosin: Type I (slow), Type II (Fast). Fast muscle can be subdived into sub-types: IIA, IIB, II C, etc. Different mammals may have different proportions of Fast and Slow muscle fibers in distinc muscles, in comparison to human, for example. Gacggt 14:23, 29 May 2006 (UTC)

See Tonic_(physiology)#Tonic_muscles. Also Muscle_spindle where there are diffuse nerve endings rather than end plates in some fibers. Contraction time and intrinsic shortening speed vary dramatically with species, so the sarcomere properties in different mammals vary significantly [1] as do myosin isoforms [2] --QuietJohn (talk) 20:08, 10 June 2010 (UTC)

Does anyone know if skeletal muscle fibres (i.e. single cells) stretch the whole length between tendons? Thanks. -postglock 09:18, 25 May 2006 (UTC)

This is probably the case, since a single muscle fibre may be thirty centimetres long. --Smajie

Cheers, thanks. -postglock 01:59, 24 October 2006 (UTC)

Myofibres of humans (possibly common to primates) strech from tendon-tendon. Sheep for instance have short myofibres that do not stretch the length of the bone, but rather sheep muscles consist of a range of myofibres over-lapping one another. Each myofibre contains one nerve cell to provide the appropriate signals. Based on this humans have less myofibres to generate force compared to a sheep, which may seem bizarre, however it does makes sense. Human muscles are actually quite slow compared to other species, however we always think we can move very fast but this is due to the length of your limbs being 1+ metre in length, as the movement of your arm near the shoulder is slow, but when you have a metre long arm attached it appears that the tip of your fingers (end of your arm) that your arm can move fast(fulcrim physics). In fact most mammals will beat humans in a proportional running race or weight lifting competition. If we go back to the sheep model, this is not too surprising considering sheep have to be able to readily avoid prey. This becomes very obvious when a non-primate is born, as these animals are generally required to be able to avoid prey as soon as they are born (i.e a newborn sheep will find its feet and begin running within minutes of its birth...if it can't stand it can't get milk). How long does it take before a human can stand, move and even run? 1year? —Preceding unsigned comment added by (talk) 01:26, 12 May 2011 (UTC)


Skeletal Muscle = Fascicle + Blood vessel

Type I (Slow) Muscle: Outside of Fascicle

Type II (Fast) Muscle: Center of Fascicle

--Smajie 06:40, 2 July 2006 (UTC) _____________ Sorry that is not true... a fascicle is just the muscle bundle surrounded by connective tissue; there is no preference of fiber types to the outside vs the center.

Gacggt 21:08, 23 June 2006 (UTC)

In pig muscle there is a distribution with slow in the centre, IIa around and IIx on outside of a fascicle.

That applies to embryonic pig muscles. The fibre type changes in utero as the animals develops (mreasured by weight). Pigs have the most organised pattern of myofibre distribution. but this becomes less apparent after birth. The feature of muscle fibres o one type surronding another type is common to almost all animals, although in embryonic fish it isn't too apparent —Preceding unsigned comment added by (talk) 01:31, 12 May 2011 (UTC)

References would be helpful to follow up such claims. — Preceding unsigned comment added by QuietJohn (talkcontribs) 06:52, 17 April 2014 (UTC)

Type 2x[edit]

"Human type IIx (aka IIB) are our fastest fibers." Is there a source that says humans have Type 2x muscle fibenpohpjpounonoun[un[i rs? Studies I've read only talk about rats and mice having them. If you respond, please do so to my discussion page as well because I can never keep up with articles. Jamesters 23:39, 16 November 2006 (UTC)

Humans do not EXPRESS (we have the genes) ATPase type IIB, nor do we express a "b" or "B" subtype myosin heavy chain. There is historical confusion over this point, but not modern confusion. --Bmeador14 (talk) 20:22, 8 January 2014 (UTC)

Pre load forces[edit]

Two questions- 1. Does anyone know what happens to muscles at its highest pre load forces? 2. What is the physiological mechanism that causes muscle to contract more forcefully when stretched? —The preceding unsigned comment was added by (talk) 12:43, 25 April 2007 (UTC).

I don't understand question one. If you give a muscle a large pre-load it will stretch (if I understand pre-load). If you keep increasing its pre-load it'll stretch until it tears. At a long enough length you can actually (in skeletal muscle) decrease thin and thick filament overlap to the point of not being able to have any actin-myosin interaciton and only extracellular stuff (collagen, elastin) is holding the muscle together. Second question, nobody knows. There is increased calcium sensitivity (more force for a given calcium), increased maximal force, some think greater cooperativity. Its called length dependent activation, and in the heart the Frank-Starling law of the heart. There are many theories, but nothing has panned out yet.Rjkd12 18:10, 18 May 2007 (UTC)


In the article for smooth muscles, sizes are mentioned. I mis that here. I found information about the size of skeletal muscle cells here: If the source meets the demands of the wiki, someone could add the info to the article.

Muscle sizes vary greatly within a species (i.e. mouth muscles vs leg muscles) and between species. This applies to both their length and width. Wild pigs have the widest myofibres, an eleaphant is comparable to humans. —Preceding unsigned comment added by (talk) 01:33, 12 May 2011 (UTC)

According to Livestock Science 116 (2008) 30 - 41, domestic pigs have larger myofibers than wild pigs. The value for wild was around 1500 square microns CSA. Experimental Physiology, 96, 539-547 shows CSA between 2000 and 8000 for humans. However, frog muscles have CSAs ranging from around 1200 to 20,000 square microns (J Physiol. Feb 1972; 221(1): 105–120.). Again, reference would help.QuietJohn (talk) 07:09, 17 April 2014 (UTC)


The individual in the picture has never competed in any sanctioned bodybuilding contest, and therefore cannot be called a bodybuilder. He may be a muscular individual, but is not deserving of the title "bodybuilder".—The preceding unsigned comment was added by (talkcontribs).

Wrong. Bodybuilder-noun- someone who does special exercises to develop a brawny musculature. [[1]] Wikidudeman (talk) 11:47, 11 July 2007 (UTC)
The definition of a bodybuilder is somone who exercises to increase the size and symmetry of their muscles. Someone can bodybuild and not compete. If he self-identifies, and has developed, symetrical muscles, he's a bodybuilder. There's no reason to remove the picture. WLU 20:00, 13 July 2007 (UTC)

unlcear phrase[edit]

types of fibers (AKA "fibers") This is either a typo or needs to be clarified/reworded. I know nothing of the subject, so unfortunately am unable to DIY it.Lisa4edit (talk) 18:43, 16 May 2008 (UTC)

Fiber Types Confusion[edit]

We need to review and correct this article, regarding fiber types and whether or not the various citations, tables etc. refer to humans or to mammals as a whole. I do not have the background to do make this corrections competently. However, as I was trying to make sense of apparently contradictory statements about fiber types, I found in Google Scholar Textbook of Work Physiology which reviews historical classification of fiber types, showing a continuum of 9 types, and that what was referred to in humans as 2b is actually 2x. Therefore the table in Skeletal Muscle, as it it refers to humans incorrectly distinguishes between 2b and 2x. Anybody up to the challenge of fixing this article accordingly?--Gciriani (talk) 14:23, 28 November 2008 (UTC)

I have started to make edits to this section. It is in a bad state. I have a Ph.D. in exercise physiology, with a specialty in molecular muscle pathology. But, I am not so familiar with Wikipedia editing, so it will take some time!--Bmeador14 (talk) 20:18, 8 January 2014 (UTC)

Table on Muscle Fiber Type Properties[edit]

I found the deletion of the table containing muscle fiber types arbitrary, and little researched. I believe that anybody with a degree in kinesiology or sport science has seen that table. In a google search I could immediately come up with the several hits: describes in word some of the same properties populating the table; has a very similar table and it's probable the author of that web page adapted it from textbooks. Also the deletion of distinction between type IIa and IIb (or IIx) in other sections of the article is a step back in encyclopedic knowledge. —Preceding unsigned comment added by Gciriani (talkcontribs) 12:27, 4 May 2009 (UTC)

human only?[edit]

Throughout the animal kingdom, are there only the 4 types of muscle fibers mentioned in this article, or are there more than that? If these represent the types of muscle fibers found in humans, the article should mention that. If other species of animals have other types of muscle fibers, it might be an interesting expansion to this article to have something about these. SlowJog (talk) 23:40, 11 September 2009 (UTC)

The types are three. Then the last row in the table explains the gene expressions found in humans, which are three. The fourth (2B or IIB) results from past beliefs, which have been corrected by more recent research. I believe that the types are valid for all skeletal muscles, no matter what the species is. However, I do not have the necessary biology knowledge to make such an entry with confidence.--Gciriani (talk) 18:18, 12 September 2009 (UTC)

Bee, and other insect flight muscle is striated ( and vibrates rather than 'twitches'. Bivalves also have striated fibers in their adductor muscles with 'catch' properties regulated by 'twitchin' (J Mol Biol. 2007 Jan 12;365(2):325-32). I'll leave it for others to ponder how the relationship to 'skeletal muscle' should be interpreted. If they shouldn't be included on this page, perhaps some kind of disambiguation would be appropriateQuietJohn (talk) 07:38, 17 April 2014 (UTC)

The article DOES NOT have 2 types of white muscle fiber[edit]

"The 2 main categories of muscle fibers become 3 when we split the white muscle fibers into 2 sections" This sentence is followed by 3 categories of muscle, 2 red and 1 white. It is the red muscle that is split into 2 sections, not the white. This sentence is wrong. I fixed this, but someone flagged my change as "vandalism" and reverted to the previous description. —Preceding unsigned comment added by (talk) 17:39, 17 November 2010 (UTC)

some comments[edit]

This topic occupies many textbooks covering biomechanics, physiology, molecular biology, anatomy, neurophysiology and probably many more. How much detail do you want for a Wikipedia article?

I think the comment on pre-load refers to the use of counter-movements to heighten performance. For example, a jump from a squatting position wont get you as high as a jump from a standing position where you first move into a squat and then smoothly transition to the jump. The muscle contraction to decelerate the squat means that the muscles are generating maximal force as soon as the takeoff begins, rather than developing force in the first part of the takeoff. This allows the individual to produce a higher total impulse (force/time integral). Another often cited effect of pre-load is the ability to store elastic energy in tendons. [Alexander R.M 1984 Elastic energy stores in running vertebrates Am. Zool 24 85–94.]

Where do you get the idea that the slow fiber energy source is triglycerides? Don't all 3 types rely on glucose? All the fiber types break down glucose by glycolysis. This is the conversion of glucose to Pyruvate with the creation of ATP. Slow fibers then break down the pyruvate to CO2 and water using the oxidative metabolism which is much less effective in fast fibers. (Slow fibers have more mitochondria which support aerobic metabolism). Fat metabolism usually kicks in later in the process as shown by respiratory exchange ratio. [Bente Kiens. Skeletal Muscle Lipid Metabolism in Exercise and Insulin Resistance. Physiol. Rev. 86: 205-243, 2006.]

You may like to use the article by Hoh as a basis for fiber types. He discusses 4 limb muscle types plus other jaw muscle types. [Joseph F. Y. Hoh. `Superfast' or masticatory myosin and the evolution of jaw-closing muscles of vertebrates. The Journal of Experimental Biology 205, 2203-2210 (2002)]. It should also be noted that 'slow' and 'fast' muscle fibers develop at different times in the embryo. [MICHAEL T. CROW The Determinants of Muscle Fiber Type During Embryonic Development. AMER. ZOOL., 27:1043-1053 (1987)]. It is very well established that the innervation of muscles plays a significant role in determining the myosin expression in muscle fibers. There seems to be confusion between fiber types and Myosin types. The Wikipedia Myosin page lists 18 types, but there are really only 3 fiber types. Slow oxidative (1), fast oxidative glycolytic (IIa) and fast glycolytic (IIb). Human myosin types are: Embryonic; Neonatal; cardiac alpha; cardiac beta or slow type I (as expressed in skeletal muscle); fast type IIa; fast type IIx/IId; fast type IIb; Extraocular; and mandibular or masticatory (m-MHC). A single muscle fiber may have more than one myosin type. The myosin type mix can be altered with exercise, pathology, hormones. [Kenneth M. Baldwin, and Fadia Haddad. Plasticity in Skeletal, Cardiac, and Smooth Muscle: Invited Review: Effects of different activity and inactivity paradigms on myosin heavy chain gene expression in striated muscle. J Appl Physiol 90: 345-357.]

A report of muscle fiber length in various human muscles can be found in [Samuel R. Ward, Carolyn M. Eng, Laura H. Smallwood, and Richard L. Lieber. Are Current Measurements of Lower Extremity Muscle Architecture Accurate? Clin Orthop Relat Res. 2009 April; 467(4): 1074–1082.]

Remember, the article explains a muscle fiber isn't strictly a single cell. Muscle germ cells are myoblasts which fuse together during development to form multinucleate myotubes. There is a Wiki (stub)article on myogenesis. The myotubes eventually become muscle fibers which current dogma assume stretch from aponeurosis/tendon of origin to aponeurosis/tendon of insertion. In some cases muscle fibers may terminate directly on bone or a septum. There are some exceptions to this, such as the sartorius muscle where muscle fibers are arranged in series [G.E. LOEB, C.A. PRATT, C.M. CHANAUD AND F.J.R. RICHMOND Distribution and Innervation of Short, lnterdigitated Muscle Fibers in Parallel-Fibered Muscles of the Cat Hindlimb. JOURNAL OF MORPHOLOGY 191:l-15 (1987)] The aponeuroses are flat, tendinous sheets which lie over the belly of the muscle and are attached to the tendons. There is a Wiki article on aponeuroses. Most muscle fibers are oriented at an angle to the load axis of the muscle and thus pull at an angle to the load axis. The angle the fibers make with the aponeuroses is called the pennation angle. Because of this structural feature, some long muscles have muscle fibers which are very much shorter than the muscle. (e.g., soleus, between 20 & 30 cm long has fibers ~4.5 cm long.) The advantage with this arrangement is that it allows many more fibers to be packed in parallel, thus increasing the physiological cross sectional area.

The description of the mechanical consequences of pennation angle in the article is a little misleading. The shorter length change is due to the muscle fibers being shorter in pennate muscles. In fact, the strange mechanics of the pennate muscle allows the tendon/aponeurosis to move a greater distance than the fiber shortens. This is known as the 'architectural gear ratio' [Emanuel Azizi,* Elizabeth L. Brainerd, and Thomas J. Roberts. Variable gearing in pennate muscles. Proc Natl Acad Sci U S A. 2008 February 5; 105(5): 1745–1750.] and is pennation angle dependent.

Fascicles are merely bundles of muscle fibers enclosed within a perimysial sheath. There are Wiki articles on fascicles and perimysium. The distribution of fiber types within a fascicle is considered to be random. [Sue C. Bodine, Alan Garfinkel, Roland R. Roy, and V. Reggie Edgerton. Spatial Distribution of Motor Unit Fibers in the Cat Soleus and Tibialis Anterior Muscles: Local Interactions. The Journal of Neuroscience, June 1968. 8(6): 2142-2152.] There are regional differences in the numbers of particular fiber types within a muscle. As there are species difference in muscle fiber type distribution. For example, cat soleus is almost 100% slow fibers whereas human muscle is closer to 50/50 fast and slow. The deep portions of Tibialis Anterior muscle in several species tend to have more slow fibers than the superficial regions. This paper is a recent one describing some of the regional differences and refers to other, older papers. [Raja Dahmanea, Srdjan Djordjevičb, Bostjan Šimuničb and Vojko Valenčičb. Spatial fiber type distribution in normal human muscle: Histochemical and tensiomyographical evaluation. Journal of Biomechanics Volume 38, 2005, Pages 2451-2459.]

Another in-depth article is R. I. CLOSE. Dynamic Properties of Mammalian Skeletal Muscles. PHYSIOLOGICAL REVIEWS Vol. 52:129-197, January 1972. Of relevance to one question above, page 166 of the article discusses the speed of contraction of muscles in different animals. It shows that there is a trend for larger animals to have slower muscles. Yet molecular biology suggests they all have similar mixes of the myosins!

There should also be a least a mention of muscle spindles and Gogi Tendon organs which also have their own Wiki pages. Which reminds me of another potential topic for the introduction which should enumerate the various functions of skeletal muscle: Cardiovascular (skeletal muscle pump - see Wiki page); Thermogenesis (Wiki aricles on Thermogenesis and thermoregulation; Protection (abdominal muscles protect delicate abdominal organs. Major nerves and blood vessels usually buried under muscles - Wiki article on Muscular Defense); Movement; Sensory (propriocepion by muscle spindles and tendon organs - Wiki has a page on proprioception); You could also add that muscles contribute to several other important functions of organisms by virtue of their integration into other systems. Muscles orient the eyes and the pinnae of the ears in many animals. Muscles assist communication (muscles of the larynx for vocalization and facial muscles controlling facial expression); Feeding (mastication and swallowing) QuietJohn (talk) 22:34, 24 May 2010 (UTC)

I don't really have time to learn the Wiki layout and formatting, but if someone wants to partner with me I'll try to help with content. It might be useful to first determine exactly how comprehensive the article should be, with some notion of who the intended audience may be. QuietJohn (talk) 04:00, 22 May 2010 (UTC)

Table: Type 2b vs Type 2x[edit]

While I agree with Mokele extending IIb to animals, I think the table may need some correction. What was written for 2b actually was originally meant for 2x. Therefore the 2b column needs checking and correcting by somebody who is familiar with type IIb in animals.--Gciriani (talk) 18:53, 7 June 2011 (UTC)

I was thinking about this after your edit, and I'm not actually sure what to do. From what I understand of the more molecular aspect of the field, it's kind of a mess right now, both in terms of how many isoforms there are as well as their functional implications. For instance, not only can you have multiple isoforms per motor unit, you can even have multiple isoforms along the length of a single myofibril. I cringe to think of what'll come out of some of tetraploid and octoploid anurans.
Anyhow, I'm very "organism-centric", so from that POV, the typical SO/FOG/FG breakdown still works pretty well in the gross sense of what the fibers metabolize, how they react to fatigue, how fast they are, etc., with the caveat that the isoforms in any of the categories can vary between species and there's a *lot* of isoforms.
For added oddness, there' yet another isoform that doesn't fall into any of the above categories - masticatory myosin (sometimes called "superfast" myosin), which has much greater force than other isoforms (best estimate is ~2x) but with a much higher cost in terms of ATP per contraction. So far, it's only ever been found in jaw-closing muscles, but last review showed it present in many mammals, some birds, turtles, and sharks (sampling is pretty poor, though, especially of "lower" species). Mokele (talk) 19:36, 7 June 2011 (UTC)

Too specialized, lacking generality and basics[edit]

The page asks for experts in molecular biology yet doesn't have muscle basics like embryology (somatic and branchiomeric), innervation, physiology (twitch / tetanus, length-tension, force-velocity, rate coding, spatial and temporal summation, motor units and recruitment), sense organs, a basic introduction to the trophic influence of nerve and exercise, denervation.

Should this page be a Wiki Portal to other pages with the more detailed content like fiber typing and molecular biology? Muscle contraction, Motor neuron, Motor pool, Motor unit recruitment, Endomysium, Perimysium, Epimysium, Myosin, Actin, Troponin, Titin, Dystrophin, Sarcomere, Costamere, Architectural gear ratio, Myocyte, Myofibril, Muscle fascicle, Striated muscle tissue, Muscle contraction, Sarcomere, Muscle fatigue, Pennate muscle and others already exist and duplicate information and images on this page. Maybe the molecular biology and fiber typing contributors should consider adding the complex details to those other pages? Is there a way to come up with all pages referring to muscle? There are also many entries for individual muscles Soleus, Gastrocnemius, Tongue, Biceps, etc. It seems to me that this page should provide an overview of striated muscle with basic explanations and direct readers to other pages for more detail. Twitch isn't defined, or even mentioned in the Cellular Physiology and Contraction section, yet is used to discuss fiber types (which precedes the Contraction section).

Wasn't 'masticatory' myosin lost in humans? Sometimes cited as a factor in the evolution of humans.

In 25 years of research in muscle physiology, in several countries, I've never heard a 'muscle fiber' referred to as a 'muscle cell' and I certainly wouldn't characterize the use of 'muscle fiber' as colloquial' as suggested in the second paragraph of the introduction.QuietJohn (talk) 09:20, 17 April 2014 (UTC)

You've raised a lot of issues, QuietJohn. I've left a message on your talk page. I completely support simplifying our Anatomy articles and would love to work with you on this. --LT910001 (talk) 10:49, 17 April 2014 (UTC)
    • ^ Close RI. Dynamic properties of mammalian skeletal muscles. Physiol Rev. 1972 Jan;52(1):129–197.
    • ^ Guillermo H. Graziottia, Clara M. Ríosa, and José-Luis L. Rivero. Evidence for Three Fast Myosin Heavy Chain Isoforms in Type II Skeletal Muscle Fibers in the Adult Llama (Lama glama). Journal of Histochemistry and Cytochemistry, Vol. 49, 1033-1044, July 2001.