Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Medical What determines the amount of force a human muscle can exert?

  1. Dec 5, 2008 #1
    For any given human muscle (the bicep for example), are there any other factors that determine the amount of force it can exert besides the amount of muscle and the "type" (red vs white, or slow-twitch vs fast-twitch)? Say, if you had a person who had .5 kg of muscle in his bicept that was 60% fast twitch and 40% slow twitch (totally pulled these numbers out of my *** btw), would that alone be enough info to determine that this persons bicept can exert X newtons of force or are there other factors that would need to be considered? TIA
  2. jcsd
  3. Dec 5, 2008 #2


    User Avatar
    Gold Member

    I'm not sure if you mean what can be exerted by the muscle itself, or by the arm that it empowers. If the latter, the attachment points to the bones (thus leverage) are important. Also the length of the bones.
  4. Dec 5, 2008 #3


    Staff: Mentor

    The cross-section of the muscle is more important than the volume for determining strength for determining the tension.
  5. Dec 5, 2008 #4


    User Avatar
    Science Advisor

    This is something that I have been wondering about for some time. Bodybuilders who pump up their muscles to show them off are not as strong as weightlifters who work exclusively to develope strength. I have always assumed that this was because of differing densities in the muscle tissues.
    What do you mean by cross-section? Do you mean the size of the cross-section, or some other aspect of it?
  6. Dec 6, 2008 #5
    A big part of that has to do with the type of muscle hypertrophy.

    Myofibrillar hypertrophy is due to an increase in the cross sectional area of the myofibrils. This will increase the tensile strength and force generating capability of the muscle and causes an increase in muscle size coupled with increased strength.

    Sarcoplasmic hypertrophy is an increase in the size of the sarcoplasm (muscle cytoplasm). This allows the muscle to store more ATP and glycogen. This causes an increase in muscle size coupled with increased resistance to muscle fatigue.

    It is just about impossible to achieve one at the complete exclusion of the other. However, powerlifters tend to favor myofibrillar hypertrophy and bodybuilders tend to favor sarcoplasmic hypertrophy.

    Powerlifters also tend to have more neuromuscular strength. I understand that they can recruit more motor neurons.
  7. Dec 6, 2008 #6


    Staff: Mentor

    Sorry, I should have said "cross sectional area". To a good first approximation the maximum tension of a muscle is proportional to its cross-sectional area. This is related to the square-cube law and explains why insects can lift hundreds of times their body weight.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook