Talk:Muscle contraction/Archive 1

Archive 1

Archive 2

Muscle contraction

I just took my final in Anatomy and Physiology I. We had to answer a ten point question on muscle contraction, including action potentials, events at the neuromuscular junction, and the sliding filament theory. This article sums up nicely what we had to learn for the test. I planned on adding my own information to this page, but once I read through it I realized no editing was needed. Good stuff! Reynoldsrapture 22:26, July 29, 2005 (UTC)

Good work. Isotonic, isometric, concentric, eccentric contraction should also be explained. --Eleassar my talk 15:04, 26 August 2005 (UTC

Last paragraph

I think the last paragraph is slightly misleading as it explains that calcium ions leave troponin after explaining smooth muscle contraction. Since there is no troponin in smooth muscle, I think this paragraph should be placed under the heading of "Skeletal muscle contraction". —Preceding unsigned comment added by 138.253.176.26 (talk • contribs) 11:51, 8 November 2005 (UTC)

Reflex

I just quickly added that a reflex isn't always unexpected. Locmotion, eating, breathing etc.. all have a reflex aspect to them. I am not a writer though, so if someone can say it more elequently I would appreciate it. I also changed a few thing about action potentials. Please make more clear if possible. Thanks. -Ryan —Preceding unsigned comment added by 70.230.117.247 (talk • contribs) 03:23-03:32, 25 January 2006 2005 (UTC)

Twitch

I have to complain about this page. "Twitching" or "twitch" redirect here but there's nothing on this page about twitching. This is unacceptable as many people use Wikipedia as a source of medical information. --Ensrifraff 06:33, 25 July 2006 (UTC)

Try the first sentence: A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle cell (called a muscle fiber) shortens. Raul654 06:47, 25 July 2006 (UTC)

That's a good clinical definition but if the word "twitching" is set to redirect here then this page would need a more comprehensive description of twitching. I must re-iterate that many people use Wikipedia for medical information and twitching is often a sign of more serious problems. --Ensrifraff 09:16, 25 July 2006 (UTC)

Need More and Corrections

I would be nice to discriminate between cardiac and skeletal muscle (Slow and Fast fibres), and mention the elastic protein titin in the organization (differences in titin are responsible for differences in stiffnes of cardiac and skeletal muscle). Difference in protein isoforms of myosin and actin, etc. Also a section on nonmuscle contraction apparatus and invertebrate striated muscle contraction is warranted. Maybe the flight muscles of flies would be good. GetAgrippa 17:24, 5 October 2006 (UTC)

There is an article on neuromuscular junction that should be incorporated into article. Further, the list of contraction is in need of correction. The last part about contraction is relevant, but the action potential I would assume has an article. There is a lot of neuroanatomy that could be included (distinct spinal cord pathways)if one is going to mention the brain to muscle need better description. Part is confusing. I would recommend just going from motor neuron to muscle and reference neuromuscular junction article and action potential article. Types of contractions like eccentric, concentric, and types of muscle fibers, oxidative metabolism , contractile protein isoforms, etc. should be mentioned. A better description of calcium metabolism is warranted or is there an article?

"The calcium causes the neurotransmitter, acetylcholine vesicles in the axon to fuse with the membrane, releasing the acetylcholine into the synapse between the axon and the motor end plate of the muscle fibre through the T tube system." This doesn't make sense and poorly worded. GetAgrippa 19:15, 10 October 2006 (UTC)

Perhaps a section on costameres and how the force is transduced from actin and myosin to sarcolemma to tendons, and how a muscle can generate isometric and isotonic force and how does it do it. GetAgrippa 23:32, 11 October 2006 (UTC)

ATP hydrolysis

This article makes it seem as though 2 molecules of ATP are required for one full cycle. This is not the case. Also, the power stroke of the myosin/actin complex is not a result of hydrolysis of an ATP molecule by the myosin ATPase but rather the release of ADP from the myosin/actin complex. The steps are as follows: Conditions at beginning of cycle: 1 ATP molecule present and the myosin head is complexed with the actin molecule. Step 1: ATP binds to the ATPase site of the myosin head causing the myosin/actin complex to fall apart. Step 2: ATP is hydrolyzed and the myosin filament takes on the "cocked" position. The inorganic phosphate is released but the ADP molecule remains attached to the myosin head as the myosin binds to an actin protomer closer to the z line than the previous myosin-binding site (majority of molecules during a concentric contraction). Step 3: The ADP molecule is released and the energy from the release causes the power stroke, moving the myosin and actin filaments past eachother. Step 4: The myosin head remains complexed with the actin molecule until another ATP molecule binds to the myosin head and frees it from the actin myosin-binding site. 128.104.105.100 19:34, 21 September 2006 (UTC)

Illustrations

It would be nice to have some illustrations of the contractile apparatus and contraction. Demonstrate the movement of tropomyosin to open active actin sites for myosin interaction, calcium release from SR, Myosin cross-bridge and the 10 nanometer ratchet along actin,etc.A picture is worth a thousand words and there are a huge number of illustrations available. GetAgrippa 17:14, 5 October 2006 (UTC)

Thank you WLU for adding the sarcomere illustration. Excellent addition.GetAgrippa 17:37, 16 December 2006 (UTC)

Smooth muscle

I rewrote the smooth muscle section. I can provide references, but most is considered fairly common knowledge. I wrote it quickly so it may need some editing. GetAgrippa 17:24, 5 October 2006 (UTC)

Smooth muscle does not contain either troponin or tropomyosin. I can rewrite the smooth muscle mechanism if no one else wants to do it. SteveD 12th November 2008. 09:58 pm. —Preceding unsigned comment added by 58.106.16.245 (talk) 10:59, 12 November 2008 (UTC)

New Sections?

This page is getting quite full and has a lot of great information. I remember seeing this page a few years ago and it didn't have 1/8 of the stuff. The writeups on striated and smooth muscle have so much info, I wonder if they should be their own page. A highschool student wanting to know the difference may be overwhelmed with the level of explanation which is at or above the graduate level. I wonder if we should have a briefer explanation highlighting the differences (ryanodine recepter types, striation, mechanism: ca2* vs MLCK) and have the very detailed stuff on their own page.

Also, there is no section for cardiac. I wonder if the "skeletal" part should be labled striated and anything prior to calcium release in the SR stay there. Above that, or below, have the differences in the induction of contraction in both skeletal and cardiac since that is the main differences. Just a few ideas. I wouldn't mind helping if others agree. Rjkd12 15:06, 1 December 2006 (UTC)

I like adding the Cardiac section differences in histology, contractile protein isoforms, titin isoforms, contractile properties and physiology, etc. GetAgrippa 22:48, 23 February 2007 (UTC)

References

I re-added the Brooks reference at the bottom - when I wrote the eccentric and concentric muscle contractions sections I used Brooks as my basic guide. It's a textbook of exercise physiology so it does provide information relevant to the entire article. It's not tied to specific sections or statements because it was used generally throughout.

I had thought I read somewhere that this was allowed (i.e. not everything has to be a numerated foot-note), but can't find it with a quick search. If anyone wants to take it out again I won't re-add unless I can find the relevant policy. WLU 20:54, 23 February 2007 (UTC)

For short articles, it's not a big deal, but for long articles, having a book listed at in the references section without tying it to any specific assertion can give a false sense of security to the reader, and make it harder to maintain the articles in the long run. (For example, certain sections of the article will probably need to be split out at some point into new articles. If the references aren't tied to the text, we won't where the reference should be listed.) It is true that this didn't use to be such a big deal, but since Wikipedia:External peer review/Nature December 2005/Errors, there seems to be a much greater emphasis on explaining where our facts come from, especially in the sciences. If you want the reference in, I won't take it out, but I think it would make the article much stronger if we could tie actual page numbers to actual statements in the wikipedia article. Do you still have the book? --Arcadian 00:14, 24 February 2007 (UTC)

I do and I still use it, it's a good book. It'd be a lot of work to go through for points and match up. I'll try reading through and if anything I remember came specifically from the book I'll try throwing in a reference. It may take me a while though. If there's anything you see as needing a reference, point it out and I'll try to find it. Right now I'm playing catch-up on my watchlist but I'll try to get to it in the future. WLU 19:52, 24 February 2007 (UTC)

Eccentric

"the muscle lengthens as it contracts." Does this make sense? Could it be explained better? Xxanthippe 10:46, 18 April 2007 (UTC)

It's the exact definition of a muscle contraction - the joint opens and the muscle lengthens despite the action of the contractile proteins. Muscle contraction is the statement used to describe the contractile proteins working. I suppose you could replace "contracts" with some reference to the muscle trying to shorten. It seems counterintuitive, but the meaning of 'contract' in the sentence is a specialized scientific/physiological one rather than the general 'becomes smaller' meaning. WLU 12:35, 18 April 2007 (UTC)

The standard linguistic meaning of contract is "gets shorter" i.e. reduces in length. Is standard linguistic usage more appropriate to an encyclopedia than counterintuitive medical terminology? Is it the case that Concentric Contraction means that the muscle contracts while under the influence of the load (the applied force) and Eccentric Contraction mean the muscle expands while under the load? Xxanthippe 11:51, 19 April 2007 (UTC)

Since this is an article about muscles, using terminology specific to muscle may be appropriate. I'll try a clearer definition.

Muscular contraction as a whole is not about the muscle shortening or lengthening, it is about the acto-myo fibers working. The two types of contractions refer to whether the muscle lengthens or shortens while working. In each case there are filaments sliding across each other, trying to shorten the muscle, it is a matter of if they are successful or not. WLU 14:43, 19 April 2007 (UTC)

I edited some of the eccentric stuff. Eccentric work isn't "not normal" or strange any more than concentric work. Muscles don't "normally" close a joint either, so eccentric work doesn't normally open one. Muscles aren't "supposed" to contract concentrically. Also, nobody knows what happens to the myosin heads during eccentric work. What they do during concentric work isn't well known either. Now there is the latch theory where the myosin head rotates at the myosin-actin interface instead of near the "hinge" region. By rotating at the myosin-actin interface it extends an extensible region in the neck (like a spring) and then contraction occurs when the spring pulls the head in. Rjkd12 18:24, 18 May 2007 (UTC)

For an eccentric contraction to occur, the force acting on the muscle must be greater than the force the muscle is producing. I'm not saying its more than the maximal force the muscle can produce, just more than its producing at that point. I agree "contraction" may not be the correct word. To contract means to shorten, and the muscle isn't shortening. I think "activated" is a better word because lengthening during activation is much different than lengthening while the muscle is relaxed. But, we should still use the term "contraction" because its still an "eccentric contraction." Remember, there are three types of contraction, eccentric, concentric, and isometric. Its an archaic term.Rjkd12 14:50, 22 May 2007 (UTC)

I was looking through my textbook for some references, and I believe I hit up against a specific statement that addresses the contract/shorten problem, i.e. that even though it implies shortening, in this context it's not necessarily shortening. I can try to provide the exact use if desired, it might help clarify the page. WLU 17:51, 23 May 2007 (UTC)

RJ, I plagiarized a chunk of your paragraph while editing the main page 'cause you said it better than anything I could come up with. Thanks! WLU 18:16, 23 May 2007 (UTC)

I object to a couple of changes that were made to my edit of May 22. First of all, I think we should use the phrase "so-called 'eccentric contraction'", since in the normal sense of the word it is not a contraction. Secondly, whether a muscle gets longer or shorter does not depend on whether the force applied is greater or less than the force generated by the muscle. Think about Newton's laws. The difference between these two forces determines the acceleration, not the velocity. It is only necessary for the applied force to be greater briefly in order to start a muscle elongation. After that, the applied force may be less. Think of someone moving a dumb-bell in a sine-wave function of time. During the bottom half of the "eccentric contraction", the muscle is exerting more force than the weight. Also, in the top half of the "concentric contraction", the muscle is applying less force than the weight. EricK 19:01, 17 September 2007 (UTC)

The term 'eccentric contraction' is the scientifically appropriate one - to use another term or attempt to justify it is to engage in original research. It is a contraction in the muscular sense that the contractile proteins are cycling, though not in the geometric sense of shrinking or shortening. I'm guessing that the term 'contracting' was used when the sole type of contraction identified was the shortening of a joint/muscle; it may be an archaic or inaccurate use in its original sense, but it's what is used in science today.

The length of a muscle absolutely depends on the forces generated - gravity or some other pull opposes the contraction of the muscle, and the muscle lengthens. The force may be below the total potential force output of the muscle, but it is still exceeding the current force output - otherwise the contraction would be isometric or concentric. It's possible I'm not understanding your comments, but right now I don't see what you would like to see adjusted on the main page based on your comments; could you suggest a wording which is more acceptable or better than what is currently on the page? Thanks, WLU 20:44, 17 September 2007 (UTC)

Well! I didn't realize I was an original researcher! And just because I think we should use the expression "so-called" in front of the term "eccentric contraction", which is neither eccentric nor a contraction! Now, THAT's original!

Seriously, the expression "so-called" is used to "imply a purported or dubious designation" (Am. Her. dictionary), which you yourself admit that it is. The term is "scientifically conventional", but not very "scientifically appropriate". Look, the issue of whether to put in the term "so-called" is a question of making the article less confusing, but it doesn't have to do with the accuracy of the article, as does my point about the forces.

I don't know how to explain the point about the forces without repeating what I have already said. Obviously there has to be a force that starts the motion. But after the arm (say) is in motion, you can stop the force, and the arm will continue to move by inertia opposite to the force applied by the muscle. However, since the forces are now out of balance, there will be an acceleration in the direction in which the muscle is pulling. Eventually this will turn the motion into a normal, "concentric" contraction.

To put it mathematically, the length of a muscle depends on the integral over time of its velocity of elongation, and the velocity of elongation depends on the integral over time of the difference in applied and exerted forces. Your way of looking at it is the Aristotelian view of motion, which was later found by Newton to be wrong.

This all has nothing to do with whether the muscle is exerting its maximal force or not.

Here is the wording I would put for the first paragraph of the section:

A so-called "eccentric contraction" is when the muscle is actually elongating (contrary to the normal sense of the word "contraction") while exerting a force opposing the elongation. This elongation is initiated by some external force (or by an opposing muscle).

EricK 15:32, 19 September 2007 (UTC)

Eccentric contraction isn't a purported or dubious term, it's a term that has a specific scientific meaning. To me, placing 'so called' seems like a weaselword-ish criticism of the term, hence my objection - the term isn't inaccurate in this context. There are other places where specialist terminology seems counter to the modern meanings of the word (In camera) and I don't see a need to point it out each time. Also, the issue is somewhat addressed in the lead. Did you want to take this to a WP:3O? Since my education was in kinesiology, the term seems natural to me so my objectivity might be somewhat suspect. Further, to add a block of text about the appropriateness of the term really does seem like OR to me, though it'd be fine to cite a discussion of the origins of the term somewhere. Other areas seem to have somewhat related issues. [1]

The problem with your above suggestion for the first paragraph is that the page is discussing muscular contraction, not another kind of contraction. Other uses of the term seem irrelevant to the page.

For the forces discussion, I'd rather move it to a new sub-heading; discussing both at the same time is hard on the formatting. I'll quote your comment and reply in a new section. WLU 16:32, 19 September 2007 (UTC)

Eccentric contraction and forces

From above section

Whether a muscle gets longer or shorter does not depend on whether the force applied is greater or less than the force generated by the muscle. Think about Newton's laws. The difference between these two forces determines the acceleration, not the velocity. It is only necessary for the applied force to be greater briefly in order to start a muscle elongation. After that, the applied force may be less. Think of someone moving a dumb-bell in a sine-wave function of time. During the bottom half of the "eccentric contraction", the muscle is exerting more force than the weight. Also, in the top half of the "concentric contraction", the muscle is applying less force than the weight. (19:01, 17 September 2007)

I don't know how to explain the point about the forces without repeating what I have already said. Obviously there has to be a force that starts the motion. But after the arm (say) is in motion, you can stop the force, and the arm will continue to move by inertia opposite to the force applied by the muscle. However, since the forces are now out of balance, there will be an acceleration in the direction in which the muscle is pulling. Eventually this will turn the motion into a normal, "concentric" contraction.

To put it mathematically, the length of a muscle depends on the integral over time of its velocity of elongation, and the velocity of elongation depends on the integral over time of the difference in applied and exerted forces. Your way of looking at it is the Aristotelian view of motion, which was later found by Newton to be wrong.

This all has nothing to do with whether the muscle is exerting its maximal force or not. User:Eric Kvaalen

An eccentric contraction only occurs when the force generated by the muscle is less than the opposing forces on the muscle/joints/bones. This can occur voluntarily (as when doing a negative while lifting weights), unconsciously (when making a movement smooth rather than jerky; I believe the cerebellum does this) or involuntarily (when you are handed something too heavy for you to hold). I'm not sure of the advantage of phrasing things in terms of sine waves and I still don't really see your point. The rest of what you've said I still don't understand, but I'm going to address the points I can from one particular paragraph I do get:

Obviously there has to be a force that starts the motion.

Regarding the human body (or other entity with muscles), the force can be generated by a muscle or from an imposed load or other force.

But after the arm (say) is in motion, you can stop the force, and the arm will continue to move by inertia opposite to the force applied by the muscle.

An arm will be in motion because a muscle is contracting, or because something else is causing it to move (gravity, inertia of an object, someone pulling on your arm). If the movement is caused by your own muscles, you can consciously stop contracting it. If it's caused by an external force, the only way you can really stop it is by dropping or escaping from a grip.

However, since the forces are now out of balance, there will be an acceleration in the direction in which the muscle is pulling. Eventually this will turn the motion into a normal, "concentric" contraction.

This would only occur if the muscle were undergoing an eccentric contraction and the load were suddenly removed, or the force output of the muscle increased. I still don't understand the implications for the page, though I'm trying.

It occurs to me that you may be thinking of eccentric contractions in terms of directions, motions or exercises, like a bicep curl is always a concentric motion and a tricep extension is an eccentric one. The classification of eccentric or concentric is based solely on if the contractile proteins are working while bringing the z-disks together (concentric), or while the z-disks are being pulled apart (eccentric). When a bicep curl bends the elbow, it is a concentric motion for the bicep and an eccentric one for the tricep. When a tricep extension straightens the elbow, it is concentric for the tricep and eccentric for the bicep. During any voluntary movement, at least one muscle is always lenghtened (eccentric) while at least one is shortened (concentric). During involuntary movements (such as a passive manipulation by another person), at least one muscle is lengthened, and the others are 'folded' or squished (as far as I know, there is no movement of the acto-myo fibers within the sarcomere). All skeletal muscle movements involve paired concentric and eccentric contractions. Eccentric and concentric are not based on comparisons to specific directions, orientations or even anatomical landmarks. The use of vectors, acceleration and velocity are pretty much irrelevant; the only way I see velocity and acceleration being involved is through a purely quantitative comparison of two different forces - if the force generated by the muscle grossly exceeds the load moved, it contracts concentrically but the change in joint position will occur much more quickly than if it is just slightly exceeds the load moved. Similarly, if the load placed on a muscle exceeds the force output of the muscle by a small margin, the muscle contracts eccentrically and the change in joint position will occur slowly; if it's a large margin, the muscle still contracts eccentrically buth the change in joint position will occur more quickly.

Contraction in this context is a biological term, not a geometric one. Any link between the different meanings is purely happenstance. That they're called contractile proteins and muscle contractions are is probably based on the early days of kinesiology and biology when they thought the muscles actually shrunk when shortening (they don't, the volume does not change). There's no actual contraction, except for the distance between tendon insertions during a concentric contraction. Contraction solely refers to the activity of the proteins within the muscle, not lengths, distances, volumes, areas or other geometric terms. I suppose it is pretty counterintuitive to someone not trained in it, but it really makes sense if you've got a kin background. All the indoctrination I faced in school might be why I'm having a hard time getting my mind around another possible meaning :) WLU 17:35, 19 September 2007 (UTC)

I tried writing to you by e-mail to avoid a long dialog on this talk page, but I got no answer.

I am not confused as to the meaning of "concentric contraction" and "eccentric contraction" as you suggest in your last two paragraphs. I do understand how the terms are used (even if I think that the terms are badly chosen).

Let me go back to what I said about Aristotle and Newton. Aristotle thought that for a motion to occur, there had to be a force pushing the object. (He thought, for example, that an arrow continues to fly because of air rushing in behind it and thereby pushing it forward!) Newton realized that this was not true--the force, or better yet the balance of forces, determines the acceleration, not the velocity.

So when you use your biceps to counter the weight of a dumbbell, the relationship between the force generated on your hand by your biceps and the weight of the dumbbell determines whether the dumbbell accelerates upwards or downwards or not at all. For instance, if you raise the dumbbell at a constant speed, the forces are EQUAL. If you lower the dumbbell at a constant speed, the forces are also equal!

Now, I realize that it may FEEL like you are exerting more force when you raise the weight than when you let it go down. But this is an illusion. It is true that you are consuming more fuel per unit time when you raise the weight at a given speed than when you lower it at the same speed. And I suppose your nerves have to fire faster. This means that you feel as if you're making more of an effort when you raise the weight--and you are making more of an effort. But the FORCE is the same--assmuming that the acceleration is zero.

I could go on with more cases, in which there is a non-zero acceleration (by the way, the acceleration can be in the same direction as the motion or in the opposite direction). But I hope this is enough and you will understand what I object to in the present article.

EricK 07:18, 27 September 2007 (UTC)

Eccentric redux

I composed a reply but haven't sent it, I'm waiting for time to re-read it.

Eccentric contraction may seem like a badly chosen term to you, but it is the term that is used and it is completely appropriate within the context of biomechanics and kinesiology. Wikipedia is not the place to pass judgement on the term linguistically because you feel it is inappropriate, though if you can find a citation discussing the origins of the term, it could definitely be added.

Note the new reference added from UCal (http://muscle.ucsd.edu/musintro/contractions.shtml), in particular,

As the load on the muscle increases, it finally reaches a point where the external force on the muscle is greater than the force that the muscle can generate. Thus even though the muscle may be fully activated, it is forced to lengthen due to the high external load. This is referred to as an eccentric contraction (please remember that contraction in this context does not necessarily imply shortening [emphasis added - note that the above does not discuss eccentric contractions during voluntary movements that are below the maximal force output of the muscles]).

When a muscle contracts, even if it is at a constant velocity, it is still doing work - in fact, work is greater at a slow constant velocity than an extremely fast one due to the constant overcoming of inertia and nature of the actin-myosin molecules. They're a billion tiny ratchets, each only does a very small amount of work before locking. Each movement requires the proteins to repeatedly release-grab-pull. Your discussion of Aristotle and Newton doesn't seem to apply here - first of all it's a biological system and not an object in space, second, all muscles and joints work through rotations, not pushes and pulls. The joint is a pivot, the bone a lever, the muscle generates force. The forces are circular, not linear.

Also, this line looks like OR, particularly given the Ucal website above that eccentric contractions are near-maximal contractions:

Even though the muscle is doing a negative amount of mechanical work, chemical energy (in fat, glucose or ATP) is nevertheless consumed, although at a lower rate than during a concentric contraction of the same force.

The muscle is still doing enormous amounts of work, it's a near-maximal contraction, all going towards putting a weight down slowly. Further, muscles do not consume fat or glucose, they consume ATP, which fat and glucose are converted into. That statement really needs a citation to be replaced in my mind. I could see that eccentric contractions require less energy since the A-M links are being torn apart rather than released by the energy molecules, but I'm not sure so I would rather see it cited than just placed on the page. If you want, we can bring this up at WP:MED or a WP:3O, I will never agree to the use of 'so-called' or any other wording that makes the term look like it is a misnomer (at least not without a reference). My undergrad degree was in Kinesiology, eccentric contraction was used all the time, never once prefaced with 'so-called' or referred to as erroneous. Also, the term should be bolded the same way concentric contraction is bolded, not placed in quotations. It is not an error, it is proper. I'm going to ask User:Arcadian (also User:Fyslee) what they think 'cause they're a doctor. I could be out of my element. WLU 13:42, 2 October 2007 (UTC)

Thank you for the reply, and for your e-mail.

Let's stop talking about whether "so-called eccentric contraction" is appropriate or not. I'm never going to convince you. That's not my main point, and I avoided using it in my latest edit, just for you! (I know that the term is used in the field of kinesiology, but it doesn't fit any of the definitions for "contraction" in my American Heritage Dictionary of the English Language!)

What I object to is the statement that the elongation is "due to an opposing force being greater than the force generated by the muscle". I don't accept your UCal reference as proof that you are right. It does not give an clear and fair representation of the facts. For instance, you point out yourself that their definition of an eccentric contraction is not inclusive enough!

When a muscle contracts in the ordinary sense of the word (what you people call a "concentric contraction") then it does work. But when it elongates (what you kinesiologists call an "eccentric contraction") then it does not do work! It expends energy, but the energy is just going into heat. Work, in physics, is equal to force times distance. For an "eccentric contraction", this is negative. I'm beginning to think that kinesiology schools don't include a class in physics! Newtonian physics do apply to muscles (or, if you rather, Einsteinian physics, but not Aristotelian physics!).

It doesn't matter whether the motion is rotatory or linear. You can replace "force" with "torque" and "distance" with "angle" if you like. The point is, if you place a heavy weight gently on a table, you are exerting more force than the load, and this causes an acceleration upwards--which means that you decelerate the object so that it doesn't hit the table with a bang. This is a perfect example of an "eccentric contraction" in which the muscles generate a stronger force than the applied force.

Concerning the amount of energy consumed, notice that I said "of the same force". Let me ask you. Do you consume more energy climbing up 10 flights of stairs, or going down 10 flights of stairs? Obviously, going up. Now, climbing stairs is (mostly) done with "concentric contractions", whereas going down stairs is done with "eccentric contractions". The amount of force is the same (unless you are accelerating, and accelerating at one rate when climbing and at another rate when going down).

As for whether muscles consume fat and glucose, yes they do. That is how they produce the ATP. The ATP is produced by your muscles, not in your liver or something.

If you want to involve other people, that's fine with me. I just hope they have some knowledge of physics and not just physique! (No offense intended!)

EricK 19:07, 13 October 2007 (UTC)

If you like, replace the word 'work' with something you feel is more appropriate, but the muscle is consuming energy and opposing the force on the muscle. The muscle is working to slow the opening of the joint. Were the muscle not contracting eccentrically, the load would drop with an acceleration due to gravity, or whatever determines the speed of an elastic object recoiling. The muscle helps control the speed. If a muscle is contracting eccentrically it is not sitting passively while the joint changes position. There may be less energy used than a concentric contraction (not necessarily true by the way, a maximal eccentric contraction consumes far, far more work than a contraction of say, 10% of your 1rm but comparing eccentric and concentric contractions of equal weights, yes the eccentric is probably less active) but the muscle is working and using up energy. Were a muscle not contracting eccentrically while a joint changed position, the movement would occur much more rapidly.

I don't understand what you're objecting to regards the statement "due to an opposing force being greater than the force generated by the muscle". If the external force is not greater than the force exerted by the muscle, why would the muscle lengthen? A joint with no forces acting upon it would not move at all. Perhaps it could use some wording tweaks to indicate that the force could be generated by an external load, spring (also a load?), air current etc. as well as an opposing muscle on the body.

A slowly lowered load is not accelerated as far as I understand the concept, it's downward acceleration is reduced by the muscle - without the eccentric contraction, it would accelerate due to gravity (or springs, elastics, whatever) at the full speed of acceleration due to gravity (springs, whatever). Again, eccentric contractions occur even if the load moved is less than the total force output of the muscle. It is not an all-or-nothing pheonomena, it's a range depending on the need of the body/person up to the maximum force output of the muscle.

My Canadian Oxford doesn't have Tension myositis syndrome (but a listing of pseudoscienctific entities would) or most recent common ancestor (but a textbook on evolutionary biology would) or Functional magnetic resonance imaging (but a textbook on medial scanning woud). Dictionaries are unreliable in some cases because they are of necessity limited in scope. WLU 18:47, 25 October 2007 (UTC)

I think we're goin' in circles. I will make one more attempt to explain the subject, but if you still don't accept my proposed change, then please get a third opinion or something.

First of all, I have never been talking about whether the load is less than the total possible force that the muscle can generate. I am talking about whether the "load" can be less than the actual force generated by the muscle.

You wrote "If the external force is not greater than the force exerted by the muscle, why would the muscle lengthen? A joint with no forces acting upon it would not move at all." Well, that's what people thought before Isaac Newton! Now we know that something can move even if there is no force applied to it. However, it cannot start to move unless there's a force applied to it. Newton realized that the balance of forces determines the acceleration, not the velocity. Let's say you are holding a book above a table and its velocity is zero. You then allow the book to push your hand down. While your hand is accelerating downwards, the muscle is exerting less force than the book. If there follows a period of time during which the book is moving down but with zero acceleration, then the muscle and the book are exerting equal forces. But then let's say you start to slow the book down so that when it touches the table it is moving very slowly. (Theoretically the velocity could hit zero at the same time as the book touches.) During this deceleration, the "acceleration" is upwards and your muscle is exerting more force than the book. And yet, your muscle is lengthening.

EricK 10:58, 30 October 2007 (UTC)

I understand the concept of velocity and acceleration. I just don't see them applying here. In a void an object would move with no forces acting on it, but muscle contractions in a void are such a minority I don't see the need to modify the page. Also, because of the structure of joints and the body there will always be forces at work. It's possible that my understanding is limited, or we're working with different vocabularies, and at this point I don't even know how you would like to see the page changed. Perhaps if you showed me a 'current versus desired' version I would understand your point better or at least re-phrase my objections.

I'm not talking about an object in a void. EricK (talk) 09:55, 17 November 2007 (UTC)

Unless the muscle relaxes completely (hence no eccentric contraction and acceleration is due to gravity), there is always a force on the book. If a load is less than the force generated by the muscle, the muscle shortens. If it's more, the muscle lengthens. When shortening, it accelerates up to a constant velocity, then deccelerates at the end of the movement. When lengthening, because the muscle is solely working to slow the change in joint angle, the results are unpredictable. The book would accelerate the joint motion, the muscle is just making it happen more slowly.

It is not necessarily true that "If a load is less than the force generated by the muscle, the muscle shortens. If it's more, the muscle lengthens. When shortening, it accelerates up to a constant velocity, then deccelerates at the end of the movement." EricK (talk) 09:55, 17 November 2007 (UTC)

In your example, at the deceleration phase, the muscle is exerting more force than before, but it's still less than the book's force on your hand. Were it equal, the book would stop moving completely; were it more, it would start moving up.

No, not true, except for the last phrase--it would eventually start moving up, after moving down. EricK (talk) 09:55, 17 November 2007 (UTC)

I'm uninterested in the effort of a third opinion, you can post this on WP:3O if you'd like. If you do so, think about what changes you would like to see on the page itself, and how to present this in a neutral manner. WLU 14:36, 30 October 2007 (UTC)

What I propose is to restore what I wrote on the 2nd of October:

An "eccentric contraction" is when the muscle is actually elongating (contrary to the common meaning of the word "contraction") while exerting a force opposing the elongation. This elongation is initiated by some external force (or by an opposing muscle).

rather than

During an eccentric contraction, the muscle elongates while under tension due to an opposing force being greater than the force generated by the muscle.

And then later, to restore the sentence,

Even though the muscle is doing a negative amount of mechanical work (work is being done on the muscle), chemical energy (in fat, glucose or ATP) is nevertheless consumed, although at a lower rate than during a concentric contraction of the same force."

If that is acceptable to you, then we won't have to go to a third opinion, which I also don't want to spend time doing.

EricK (talk) 09:55, 17 November 2007 (UTC)

<undent>That qualifier is the only difference I see between the compared sentences, and again I see no value added in adding a qualifier when the term in mainstream in exercise physiology and kinesiology. The term defined is 'eccentric contraction', which is different from simply 'eccentric'. For the amount of work, you would need a reference stating that there is a difference between the amount of energy consumed during an eccentric versus concentric contraction before it could be added. I'm not sure, and I believe the literature is equivocal on this matter. It's also somewhat dubious since at sub-maximal loads, I don't know if the myosin heads are released by force or ATP binding, and a maximal eccentric load is heavier than a maximum concentric load. Also, fat and glucose are not consumed, ATP are; fat & sugar are converted to ATP. These are the same concerns I had before, and the same responses. WLU (talk) 19:24, 26 November 2007 (UTC)

Third opinion

I had to do a good deal of research before I could properly evaluate the dispute here, but it appears to be in two parts:

• The addition of a qualifier explaining that "contraction" is used outside of it's normal meaning.
• The addition of a sentence explaining chemical energy is consumed even though the muscle is doing negative work.

To simplify matters a concentric contraction uses contract in it's truest form: the muscles are indeed getting shorter. An eccentric contraction departs from the norm in that it's really a negative contraction. In reading over both methods for explaining this, I tend to lean towards "During an eccentric contraction, the muscle elongates while under tension due to an opposing force being greater than the force generated by the muscle," as preferential. The qualifier seems to imply that contraction is improperly used. However, for us to make such a leap it must be verifiable. In other words, a reliable source must indicate that the usage of the word contract is improper, since that (seemingly) is what the qualifier indicates. One could easily read "eccentric" to imply "negative" in this context, which would imply a "negative contracting" or "expanding." That being said, it may be appropriate to add properly sourced information explaining why it's called an eccentric contraction in laymen terms, as I'm sure it's well documented.
The second issue is a little less complicated. For information to be included in Wikipedia it must be verifiable, which is a higher standard than simply true. Per the diffs, the suggested addition doesn't seem to be cited and is obviously somewhat controversial, as seen by the argument here in addition to what an average person might deem common sense. The claim that a negative workload requires positive energy to perform seems to violate logic, even though further study would explain why it does not, so inclusion must not only be verifiable but expanded to explain why it is the case. If a proper source can be found to verify the claim, I would certainly support its inclusion. Justin ^chat 08:11, 4 January 2008 (UTC)

Was an actual 3O request put in or is this a 'drive by' 'cause you saw the discussion? Either way I appreciate it. And for clarity, do you mean usage of the word contract is improper or usage of the word concentric contract is improper? WLU (talk) 18:10, 4 January 2008 (UTC)

There was a WP:3O request made, and that's how I found my way here. And to clarify, I meant that to qualify the word contraction is used improperly, we must first find a reliable source saying it's used improperly. My methodology for coming to this conclusion is that "eccentric contraction" might be literally translated as "bizarre shortening". As such, I simply don't see the necessity r implying the word is used incorrectly. Justin ^chat 18:50, 4 January 2008 (UTC)

OK, thanks for the clarification. If I read your 3O correctly, your opinion is to retain the current version. WLU (talk) 19:01, 4 January 2008 (UTC)

Eric here. I, naturally, am not satisfied with this third opinion. For reference, here is what I put at WP:3O:

1. Talk:Muscle contraction#Eccentric, continued in the sections "Eccentric contractions and forces" and "Eccentric redux". A long dispute concerning whether the opposing force in an "eccentric contraction" must necessarily be greater than the force exerted by the muscle (at all times, not just initially). Also on a comment to the effect that the term "eccentric contraction" is used in a sense contrary to the usual meanings of these terms, and also on a proposed sentence concerning whether less energy is consumed in "eccentric contractions" than in "concentric contractions" for the same amount of force. The proposed changes are summarized at the end of the discussion. 16:17, 2 January 2008 (UTC)

First of all, Justin didn't discuss at all the most important question, namely whether the opposing force has to be greater than that exerted by the muscle--in fact, his suggested wording continues this fallacy.

Secondly, I disagree that in order to add my proposed parenthesis "(contrary to the usual meaning of the word contraction)" we need to prove that this use is improper. By the way, as I understand him, Justin seems to be saying that since the phrase "eccentric contraction" sounds like it means "bizarre shortening", it's so obviously an unconventional usage that there's no need to say so! So he agrees with me that it's a strange usage. I think it would be helpful to point this out to the reader, to avoid confusion.

Thirdly, concerning energy use, Justin objects to a sentence saying that the work done is negative but energy is nonetheless consumed, because he find it illogical that this negative work could use a positive amount of energy. But that was not our dispute. Of course the amount of energy consumed (fuel burned) is positive--our bodies do not create high energy molecules (fuel) when we do an "eccentric contraction"! The dispute was over whether the amount of mechanical work was negative, and secondly whether the amount of fuel used is less than for the opposite concentric contraction. To support this I gave the example of the fact that you get much more out of breath if you climb 10 flights of stairs than if you go down 10 flights of stairs. I think it's ridiculous to insist that such a fact, known to everybody, needs to be backed up with a reference. The point is that this fact (which everybody knows) shows that less energy is used for an "eccentric contraction" than for the corresponding "concentric contraction". I'm sure one could find this in a book somewhere if one looked through many books in the library, but to me it's so obvious that I don't see why it needs a reference. It's simply logic.

I intend to bring this dispute up on WP:MED, as you also suggested.

EricK (talk) 16:24, 5 January 2008 (UTC)

1. What do you propose causes the muscle to lengthen if it's not an opposing force greater than the force of the muscle contracting?
2. If you can source your qualification, it's possible to be added. That you think it's a misnomer doesn't make it a misnomer, but a source would settle this dispute.
3. If you can source the statement about energy, you can put it in. The problem is, you think there's a need for another needless qualification, when others disagree. First just me, then a separate editor with no preconceptions.

I had already posted a comment at Talk:WP:MED 07/10/03 and got no response, but feel free to do so again. It's possible this isn't the appropriate wikiproject and that's why it got no attention.

If you're still not satisfied, consider a WP:RFC. WLU (talk) 17:26, 5 January 2008 (UTC)

If I respond to these, I would simply be repeating things I have already said. For example, there has to be an initial force greater than that exerted by the muscle, but not necessarily for the duration. EricK (talk) 07:23, 7 January 2008 (UTC)

WLU suggested requests for comment, and I would also consider mediation. I will point out that a great deal of the content disputes for this article could be resolved by providing citations for all areas where a disagreement exists. Justin ^chat 18:29, 5 January 2008 (UTC)

Note per WP:PROVEIT, the burden is on the individual who wishes to add information, not the individual who removes it - I agree that a reliable source supporting your points will resolve this completely ErikK, and enhance the page. WLU (talk) 18:46, 5 January 2008 (UTC)

In response to above - muscle generates force continuously through ongoing cycling of cross-bridges, it's not a piston. If the initial force was strong, but then immediately stopped, the muscle would stop moving, or more probably concentrically contract unless consciously stopped by the person. The contraction of muscles is very finely tuned, eccentric contractions only happen when a person wants them to (through consciously limiting the contraction of the muscle to allow lowering) or when the muscle's total force output is overwhelmed. Initial or ongoing doesn't matter, if the muscle's force output is less than weight or opposing force generated through any means, the muscle lengthens. WLU (talk) 16:34, 7 January 2008 (UTC)

Removed link

The following link from the EL section has disappeared. Anyone know why?

• {{McGrawHillAnimation|physiology|Action%20Potentials%20and%20Muscle%20Contraction}}

WLU 01:09, 22 May 2007 (UTC)

False Dichotomy

Please do not state that muscle contractions are either isotonic or isometric. This is a provably false dichotomy, as seen by many MANY experiments in vitro and in vivo. Strain trajectories of muscle are complex, as are force profiles over these trajectories. Please actually *read* the references added, as well as the work loop page. During a contraction, a muscle may be activated while still being lengthened by antagonists, then briefly pass through isometry before shortening at a variety as forces as the muscle traverses the force-length-velocity-activation profile. Indeed, by simply changing the phase of activation in a work loop trajectory, an organism can change a single muscle from a motor to a strut to a brake. Please do not rely on the oversimplifications of Freshman anatomy texts. If you want a textbook, use Lieber's book: http://www.amazon.com/Skeletal-Muscle-Structure-Function-Plasticity/dp/0781775930. HCA (talk) 18:44, 8 June 2015 (UTC)

I recently reverted two edits ([[2]], [[3]]) by HCA on the classification of muscle contractions as either isometric or isotonic, with the latter subdivided into eccentric and concentric. HCA asserts that this distinction is an oversimplification and instead stated there are four types of contractions. HCA listed six journal articles from the Journal of Experimental Biology (JEB) to support this statement. I have looked at the JEB references and they do not classify contractions as four distinct contractions. In fact, the articles do not even attempt to systematically define the different types of muscle contractions. To say that they do would be to commit original research (WP:OR). I don't dispute that the present categorizations are oversimplifications. But the information from Wikipedia should reflect the general consensus from mainstream (often secondary) sources and how the terms are normally used. The distinction between isometric and isotonic contractions based on force and length is very well established in many secondary sources (e.g., see the first five references in this article). I am happy to expand the text to discuss these oversimplications. But I can't agree to wholesale disregard of mainstream sources. danielkueh (talk) 18:49, 8 June 2015 (UTC)

First, do not engage in strawman arguements. I did not, here or elsewhere, state that there are N categorical types of muscle contraction (for any value of N). My point is the exact opposite, that actual contractions do not fit the "either-or" category of your source, which is provably true (see any of the papers I linked). Non-isometric contractions do NOT have to be isotonic - see the papers and the work loop page. Indeed, the claim that "Muscle contractions can be described as either isometric or isotonic" is so clearly unrealistic, I would like you to quote for me the entire paragraph of the text this came from, to ensure you or the author hasn't badly mis-interpreted something. Extraordinary claims require extraordinary evidence, and that claim is truly extraordinary. HCA (talk) 19:24, 8 June 2015 (UTC)

That is not a strawman argument. In fact, it is not even an argument. I merely described what your edits. So don't be ridiculous and learn to assume good faith (See WP:AGF). You want direct quotes, here they are:

• From Widmaier et al. (Vander's Human Physiology): p. 263:

"When a muscle develops tension but does not shorten (or lengthen), the contraction is said to be isometric (constant length). Such contractions occur when the muscle supports a load in a constant position or attempts to move an otherwise supported load that is greater than the tension developed by the muscle. A contraction in which the muscle changes length while the load on the muscle remains constant is isotonic (constant tension).

Depending on the relative magnitudes of muscle tension and the opposing load, isotonic contractions can be associated with either shortening or lengthening of a muscle. When tension exceeds the load, shortening occurs and it is referred to as concentric contraction. On the other hand, if an unsupported load is greater than the tension generated by crossbridges, the result is an eccentric contraction (lengthening contraction)."

• Here's another one by Loudon et al for Clinical Mechanics and Kinesiology, p. 51 [[4]]

"Isotonic exercise provides a contraction in which movement is performed and therefore change in muscle length occurs. There are two types of isotonic contractions: concentric and eccentric."

That is just one of the five to six references. You can look up the rest yourself. Also, I just took a quick look at Lieber's book, which you suggested. Interestingly enough, I searched for definitions of isometric and isotonic and here is what I found.

• p. 60, "The force-velocity relationship describes force generated by a muscle as a function of velocity under conditions of constant load (i.e., "isotonic conditions).
• p. 108, The force-velocity relationship describes isotonic behavior, muscle contraction velocity at constant load.
• p. 313, In the isometric contraction panel, muscle length was held constant while muscle was stimulated for ....
• p. 61, contractions that permit the muscle to shorten are known in "muscle lingo" as concentric contractions. The word "concentric" in this context does not make no sense, but it is traditionally used to describe shortening contractions of muscle.

Seems consistent with the present status of this article and with the other references. So I have listed my references and I have looked through yours. So unless you can provide a preponderance of secondary sources that explicitly state that isometric or isotonic contractions are not defined this way, then there's really nothing more to discuss. danielkueh (talk) 19:50, 8 June 2015 (UTC)

Please, please, read my actual words, not what you think I said. I never said isometric and isotonic aren't real. I said those are not the only two options, and that real muscle contractions are more complex. Read the Widmaier quote again. It correctly described both types, forgets about isovelocity (so much for quality of that text), but never once states that those are the ONLY two types. The Loudon quote simply says that if the muscle is contracting against a constant force, it can either shorten or lengthen, which does not say non-isotonic contractions don't exist. Neither do any of the other lines you quote from Lieber.

I am not suggesting these types aren't real. I am objecting to your WP:OR that they are the ONLY two categories, and I quoted from the page. Can you provide any source that states that there are only Isometric and isotonic, with absolutely no other type possible? Can you reconcile that with the references I gave empirically proving otherwise? HCA (talk) 20:02, 8 June 2015 (UTC)

@HCA, You claimed that "muscle contractions are either isotonic or isometric. This is a provably false dichotomy." Is that no what you said? The definitions and quotes above suggest otherwise. If you don't like the word "category." That is fine. But that term is not used in the present sentence in the article. The present sentence merely says you can describe contractions as either isometric or isotonic, with concentric and eccentric being subcategories of isotonic. This is essentially a paraphrase of the Widmaier reference as well as the Loudon reference. The sources are pretty clear, isometric is not isotonic. And if it is isotonic, it can be eccentric or concentric. There is no original research. I am not "analyzing" or "synthesizing" any information to "reach or imply a conclusion not stated by the sources (see WP:OR)." In fact, none of your sources directly contradicts what is written about isometric, isotonic, etc. in this article. You can throw as many JEB articles as you want, but as long as they don't define these terms (isometric, isotonic, etc) explicitly, they are irrelevant. danielkueh (talk) 20:18, 8 June 2015 (UTC)

I would like to invite other editors reading this discussion thread to comment. Please take a look at the descriptions of muscle contractions in the lead and in the main body of this article. If you can, please take a look at the supporting references. If not, just read the quotes above and let us know if you feel that the present text in this article is not supported by the references. Thanks. 20:28, 8 June 2015 (UTC)

Your paraphrasing is wrong, which is the source of the problem. That's what I'm trying to get through to you, and you keep missing. Muscles contractions can have a variety of strain trajectories, some very complex, in vivo. Muscle contractions can have a variety of force profiles, some very complex, in vivo. Now, pay very close attention to this part, because this is key. "Isometric" and "Isotonic" are special cases that are easy to understand/teach, easy to do experimentally, and allow you to quantify the fundamental properties of a muscle (you do a series of isometric contractions at different lengths to find the LT curve, a series of concentric isotonics at different forces to get the FV curve). The texts you quote have correctly defined those terms, and the special cases to which they refer, and use them to explain these curves. But those special cases are NOT the sum total of everything muscle can do or does. That is my point, and that is my problem with the current phrasing. The current phrasing wrongly states that in every single case, "Muscle contractions can be described as either isometric or isotonic". My point, for the third time, is that those are special cases, and in vivo movements are very diverse. My point is that NONE of your references support the exclusionary classification you have inserted. Yes, isometric and isotonic are real, yes we should talk about them, but they are NOT the sum total of all muscle contraction. HCA (talk) 20:31, 8 June 2015 (UTC)

@HCA, It's a bit difficult to respond to your comments because you seem to be presenting a moving target. I can only go by your two edits, which state:

"Muscle contractions can be characterized by the length change which occurs: muscles may [[#Eccentric contraction|lengthen]] (eccentric contraction), [[#Concentric contraction|shorten]](concentric contraction), or [[#Isometric contraction|remain the same length]](isometric contraction). If force remains the same during the contraction, it is termed "isotonic". However, in real-world, in-vivo contractions, muscles may stretch, shorten, and vary force all within the same contraction, so these categories are by necessity simplifications "

and:

Muscle contractions can be characterized by the length change which occurs: muscles may [[#Eccentric contraction|lengthen]] (eccentric contraction), [[#Concentric contraction|shorten]](concentric contraction), or [[#Isometric contraction|remain the same length]](isometric contraction). If force remains the same during the contraction, it is termed "isotonic", though muscles may vary force throughout contractions when used in vivo.

It is not clear to me what alternative you would like to see replace the current wording because your recent edits are not consistent with the sources in the way they categorize and describe these four contractions. You have already conceded that the sources are correct, so I am not sure what we're disputing about here.

If you feel that the present wording appears to imply that isometric and isotonic are the sum of all muscle contractions and would like to reword it so that it doesn't, then we can certainly discuss that. My question is what other contractions do you have in mind that you would like to include in addition to isometric and isotonic? I can suggest that we add isokinetic as a third higher level category. According to p. 50 of the Loudon reference, the authors state that "The major types of muscle contractions are isometric, isotonic, and isokinetic." So if you like, we can add isokinetic into the lead and text. I have no objections to that. danielkueh (talk) 21:01, 8 June 2015 (UTC)

In what way are my edits inconsistent with the definitions? "Isometric" = same length, "concentric" = shortening, "eccentric" = lengthening, "isotonic" = constant force, "isokinetic/isovelocity" = same speed. These aren't exclusive - an eccentric contraction can be either isotonic or isovelocity (but never both over substantial length changes, because the LT effects). To properly conceive of basic muscle physiology, you need a graph with 4 spatial dimensions - length, velocity, activation, and force, all orthogonal, and even *that* fails, because it does't include history-dependent effects like stretch-induced force-enhancement or shortening-induced deactivation.

What we need for the article is two things: 1) we cannot, and will not, imply that these categories are exclusive and that all muscle constractions fall within them, as that is flat-out wrong, and 2) we need to explicitly state that, although we will define these special cases, in-vivo contractions do not typically fit into these categories. The latter is the entire reason Josephson invented work loops, after all - the above cases were easy to do in the lab but not realistic.

In fact, I think you should familiarize yourself with the work loop article before further editing, and think carefully about how those work loops play out in terms of instantaneous muscle force, velocity, shortening/lengthening, etc. In a single work loop contraction, a muscle can be eccentric, then isometric, then concentric, and force and velocity are never constant. These actually describe in vivo cyclic muscle movement far more accurately than the special cases, especially if the strain trajectory and activity phasing are experimentally derived - they were originally used to study locust flight muscle, but have since proven good matches to many other cyclic locomotor muscles (quail pectoralis, carp axial muscle) and non-locomotor muscle (treefrog calling muscle).HCA (talk) 21:27, 8 June 2015 (UTC)

@HAC, I find your reply about your edits to be a little disingenuous given that you did not even not mention isovelocity in any of your edits. In fact, in one of your other edits, you even removed isotonic altogether. It's puzzling given that you agree with the sources in the way they defined isotonic contractions. Plus, I'm assuming you also agree with the sources when they described eccentric and concentric are variations of isotonic contractions. Yet, you changed the text to make it read like that there are four major levels of contractions: isotonic, isometric, concentric, and eccentric. Your organization implies that concentric and eccentric are not variations of isotonic contractions. And that is NOT consistent with the sources. Finally, none of your six JEB references directly support your edits. So yes, we are done discussing your previous edits as potential alternatives to the present text.

As for organizing and presenting information in this article, I can only reiterate that the present text in this article, like all other introductory biology/physiology/medical textbooks, merely aims to describe the different types of contractions that exist when you control for all other variables except for the ones you are interested in. Are these contractions idealized? Absolutely. Are they a little simplistic? Absolutely. Are some of the definitions potentially misnomers? Absolutely. Are they vertebrate-centric? Absolutely. Can we add qualifications? Absolutely. But please bear in mind that the "threshold for inclusion in Wikipedia is verifiability, not truth" (WP:VNT). This is not a peer-reviewed article written just for just Ph.D. level scientists. The information here is not meant to be cutting edge (see WP:NOTJARGON). According to WP:OR, "Wikipedia is a tertiary source." We have to try to FIRST introduce the topics in a way that is consistent with secondary sources. And ideally understandable to individuals with nothing more than a high school education. ONLY THEN, can we start adding qualifiers to explain or guard against oversimplistic descriptions. We can work on that. That is not an issue.

As for the specifics:

1. If you would like to add a sentence such as "in vivo contractions do not typically fit into these categories" or something to that effect, we can do that. But please provide at least two secondary sources, in the form of a review article, textbook, or monogram. Direct quotes would be nice too. It's not that I don't believe you, but I would like to see this article be well-sourced so that we can remove the annoying banner at the top of this page. And please format the references properly. If you are not sure how, then take a look at (WP:CT). That is the least you can do given that I have spent an excessive amount of time of quoting references for you and actually looking over at your references.
2. I will not agree to the use of the term "special case." The sources do not use that term or describe them as such. And neither should we. Remember, WP is a tertiary source. We can include other descriptive qualifiers that state muscle contractions in vivo are often complex and multifaceted or something to that effect. Just be sure to provide the sources, see #1.

Now, if you don't mind, I am off for dinner. danielkueh (talk) 22:30, 8 June 2015 (UTC)

@AHC, I have made some tweaks to the second lead paragraph. It is just temporary but I would like to know if you find to be more acceptable than the present paragraph:

"Muscle contractions can be described based on two variables: length and tension.[1] A muscle contraction is described as isometric if the muscle tension changes but the muscle length remains the same.[1][2][3][4] In contrast, a muscle contraction is isotonic if the muscle length changes but the muscle tension remains the same.[1][2][4][3] Furthermore, if the muscle length shortens, the contraction is concentric.[1][5] But if it lengthens, the contraction is eccentric. In natural movements that underlie locomotor activity, muscle contractions are multifaceted as they are able to produce changes in length and tension in a time-varying manner.[6] Thus, length and tension are unlikely to remain constant when the muscle is active during locomotor activity"

Again, this edit is not intended to be final. As you know, the entire article itself is still undergoing some changes. danielkueh (talk) 00:14, 9 June 2015 (UTC)

YES!!! That's *exactly* the sort of edit I was hoping for! My objection has *always* been to the excessively simplistic, either-or "isometric vs isotonic" situation that is not reflected by reality. I realize all the stuff about readability and such (seriously, you should have seen the intro in reptile before I took an axe to it), but at the same time, it can't be actually inaccurate.HCA (talk) 01:58, 9 June 2015 (UTC)

Ok, great. Wonderful. I am glad we came to a consensus! I will change it now and the main text as well. This article on a whole is still a bit of mess. I am trying to clean it up a bit. Any help would be appreciated. danielkueh (talk) 02:10, 9 June 2015 (UTC)

muscle contraction

what happens during the contraction phase that makes muscles contract? Do the muscles gain more vitamins, lose vitamins, etc. ??? HELP!!! — Preceding unsigned comment added by 162.222.253.2 (talk) 22:03, 22 April 2016 (UTC)

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