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Power required for muscles to hold object up

  1. Oct 10, 2009 #1

    Pythagorean

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    Is there a simple theory for this in terms of mechanics?

    I'm not quite sure how to frame this. I guess you could look at it as a piston being held up by a pressurized chamber that has a constantly open release valve on it, but also an input valve that you have to keep supplying (to equal the release valves volume exhausted).

    Do I have to go to the biology subforum now to find out if the bond holding my muscles together has to be supplied with energy (ATP, I presume) or the bonds would break and my arms would drop, much like if we stopped supplying the the pressurized chamber above?
     
  2. jcsd
  3. Oct 10, 2009 #2
    I'm not quite sure what you are asking.

    It takes perhaps 2500 calories daily of energy to power a typical human body....that includes exercise (work, as in force times distance) but the body also requires energy to maintain, repair and operate life functions...somebody must have typical data for such life maintenance functions..digestion, blood circulation, breathing, etc...

    The issue you may be addressing is if one holds up, say, a one lb object the person will use more energy (calories) than if they were not holding such a weight. That's an incremental increase in energy and likely sports medicene or a related field would have observational data on such efforts over and above life functions.
     
  4. Oct 10, 2009 #3

    Pythagorean

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    Well, I posted this in the physics forum with the first paragraph in mind, but then kind of answered my question and had a second question in mind (second paragraph).

    I'm more interested in the mechanism, not the numbers.

    Like, if I'm holding a weight up, I'm obviously burning energy the whole time to do it, even though there's no motion. So what happens here? Are the bonds between the muscle cells temporary and must be supplied energy to keep bonded so that the muscle stays contracted?
     
  5. Oct 11, 2009 #4

    Andy Resnick

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    Muscle contraction occurs via myosin and actin. Briefly, myosin hydrolyzes ATP in order to 'walk' along an actin filament.

    Reality is a bit more complicated and this website is excellent:

    http://people.eku.edu/ritchisong/301notes3.htm

    You are asking about the physiology of an 'isometric' contraction

    http://muscle.ucsd.edu/musIntro/contractions.shtml

    None of the websites mentioned if isometric contractions are similar to stalling the myosin motor, but I think that's what happens:

    http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1366860
     
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