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Pivots and rotational velocity

  1. May 30, 2006 #1
    I'm trying to work out the science of a simplified model of the human body, and I would appreciate your help on some of the basic formulae.

    If I have a bar (representing the shoulders), which has a central pivot point, connected by a unrestricted hinge to a rod (representing the upper arm, connected by another hinge that only has 180 degrees of movement (representing the forearm and the elbow), connected by another hinged joint to a lump representing the fist, what formulae can I use to calculate the effects of:

    twisting the "shoulder"
    extending the "forearm"

    My ultimate goal is to calculate the optimum way to deliver force to the fist in a whipping motion.

    How much more complicated does it make it, if I allow the "shoulder" to have rotation around the x axis (simulating a shoulder roll) as well as around the y axis?

    Many, many thanks in advance!
  2. jcsd
  3. May 30, 2006 #2


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    I think that this depends an awful lot upon what sort of accuracy you want. You must know, from your expert knowledge of anatomy (which I've been led to believe is a core element of martial arts), that the human body can't be that easily modelled. My interest in designing prosthetics a couple of decades ago taught me that there's far more involved than simple leverage and rotation. There's a site somewhere, which I must have been led to from here (since I don't net-surf), that apparently is offering the ultimate fighting technique based upon physics. From what I saw of it, it just might have all of the information that you want. Unfortunately, it'll take me quite a while to find it again. When I do, I'll send you the address.
  4. May 31, 2006 #3
    Oh I think just a very simplistic level of accuracy will be more than adequate for exploring the principles in the grossest sense.

    I'm really looking for a basic understanding about the transmission of force down the various joints.

    I've heard about various styles that are created around a detailed scientific model. I've also heard that they tend to lack power. Much as we try to model the human body, there seems to be that something extra in expert martial ats that that cannot be explained by maths alone...

    That said, I'd really appreciate your link when you find it. Thanks.
  5. May 31, 2006 #4


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    Whipping the fist is not likely to be a very effective method of fighting.

    Everyone who hits hard does so using the entire body, and especially the legs and hips.

    From an energy perspective it should be relatively easy to predict the power of a strike by looking at how much muscle is used.

    This suggests that the hardest possible strike is likely to be something strange, dangerous, and really insane like be starting standing square in a semi-crouch, and then exploding upwards with both legs, the back, and the neck to strike something using the back of the head.

    The closest practical approximations would probably be an uppercut of some variety

    For the purposes of fighting there is a conflict between things that allow striking harder (eg. like squareing up) and things that provide reach or defense (eg. using a lead foot).
    Last edited: May 31, 2006
  6. May 31, 2006 #5


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    Hey, matb, I found it. I forgot that it was a commercial site, but here it is anyhow. http://www.turtlepress.com/Fighting_Science_p/fs.htm
    In addition, a quick Google of 'physics of martial arts' turned up a lot of hits. Some of them might be more useful.
  7. May 31, 2006 #6


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    Oh dear lord. A woman who has no experience in biomechanics writing a book on the subject. Matb, this is a very involved area and these conversations always pop up amongst people in martial arts. If you look at a reference on something in this area, make sure the author has some sort of verified credentials. If they don't, they are usually going off of experience and seat of their pants explainations.

    The fact is is that there is no easy way to get a good handle on biomechanics like this because they are so involved. In case you don't believe me, take a look through some real papers on subjects that are related:


    What styles are you referring? Also, DO NOT get caught up in the mysticism of martial arts. That is the area of most charlatains and people who want you to believe they are something special when they are not. Just because something is difficult to explain or describe accurately does not mean it is mystical.
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