step1doc
Forum Newbie
Topics: 6
Posts: 37
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hi friends,
i was wondering if someone could please explain the concept of isometric contraction[example in skeletal muscle]?how can the muscle length remain the same during isometric contraction even though there is sliding of actin and myosin filaments?wouldn't sliding cause muscle shortening due to shortening of the sarcomere? ?
anybody who can throw more light on this issue?any help is appreciated.thanx.
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| kmp
Forum Elite
Topics: 38
Posts: 311
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Isometric contraction there is generation of force with out shortening.
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| step1doc
Forum Newbie
Topics: 6
Posts: 37
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hi kmp,
thanx a lot for the response.how can there be no shortening even though there is sliding of actin and myosin filaments and shorteneing of sarcomere?will appreciate any help.thanx for u'r time.
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| renin
Forum Newbie
Topics: 12
Posts: 16
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c i feel dis.
the cross bridge cycling cud do 2 things.
1. active tension development
2. active shortening
in isometric contraction ... when d afterload can't be reached ... d muscle doesn't shorten ... so only d (1) happens. not d (2)
correct me if i am wrong
renin
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I agree with Renin.
Isometric contraction is an experimental condition where muscle length is fixed so muscle can not shorten, all it can do is to generate active tennsion, even when there is crossbridges cycling.
Pls correct me if I am wrong.
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| mani
Forum Guru
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explainations given above are correct but questions remains that how it to posssible to have without shortening? i think it happens so due to stretching of non contractile components like connective tissue
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| vrach
Forum Junior
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When the afterload is very large, the muscle is contracting, i.e cross-bridges are cycling, but the force (active tension) being generated is insufficient to overcome the afterload. So the sarcomere will not shorten.
A simple way I tried to overcome this dilemma is, imagine a person runnig on a tread mill. They won't be able to move forward unless they can run faster than the tread mill. Same thing applies to someone trieng to move a brick wall. They are doing work, generating force and tension, but can nerver move the wall (analogous to shortening of the muscle). Hope I haven't confused you further!!!
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| dinka kartinka
Forum Newbie
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what happens is, if there is overlap between actin and myosin fibers, it is possible to have an isometric contraction. During the isometric contraction you have bridging of actin and myosin fibers, and cycling of the cross-bridges, which is maintained by ATP. This is what contracting muscle is, it doesn't necessarily have to shorten.
I'm not sure if this is what you are looking for... I hope it was clear. 
dinka
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| mildus
Forum Guru
Topics: 19
Posts: 614
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I think that sarcomere shortens but elastic components stretch. (Muscle has both contractile and non-contractile components. Non-contractile components can be: parallel and serial.) They stretch, sarcomere shortens and neto length remains the same.
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| ssrpk
Forum Fanatic
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well this elastic stretch may occur in vitro but cannot occur in vivo [simulate isometric ontraction in vivo -try to lift 1000lbs signle handed] ;only active tension develops ........ but is not sufficient to overcome afterload ...... however if it were to lift the load ,active tension will develop untill and unless it equalizes the afterload ,thenafter any extra energy tht the muscle can spend will be utilized not generaTE active tension but for active shortening!
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| melcon
Forum Newbie
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hi,
in an isometric contraction, there is no shortening of the sarcomere, even though there is crossbridge cycling. true isometric contractions can't occur in the intact body, due to the elastic components, which would allow for a degree of stretch during contraction.
think of it in this way - a 10 year old girl tries to lift a 400kg desk. (not gonna happen!) her arm is straight, and her bicep muscle is undergoing crossbridge cycling like crazy, but the muscle is not shortening at all. the force needed for her to lift that 400kg desk is far greater than the force that her tiny little bicep muscle can produce.
hope that helps!
mel
Edited by melcon on 08/21/05 - 12:54 AM
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