Talk:Muscle contraction

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[edit] 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

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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.[citation needed]

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)

[edit] 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)

[edit] 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)

[edit] Diagram

I've asked at commons:Commons:Graphic Lab School/Images to improve#Translation German-->English for the current diagram to be translated. If you can help, please do. There are some problems with the image right now, so I'm putting it here. As it changes, keep an eye out for a point when it's ready for showtime, and stick it in there in place of the German version. Thanks! – Mike.lifeguard | @en.wb 14:01, 17 December 2007 (UTC)