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Thread: How Biomechanists Define Movements

  1. #1
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    How Biomechanists Define Movements

    Kelvin asked me to post the following - Jeff



    Universally Accepted Scientific Terms and Definitions



    Let’s start with the simple definitions that everyone should know. You can read Dr. Rob Neal’s paper to get an idea of how biomechanists measure and define the terms.

    http://www.golfbiodynamics.com/admin...-2008_rev1.pdf

    Here’s part of a paragraph from page 4 detailing the standardized process by which biomechanists define the movements. Pay special attention to the highlighted sentence in bold:

    The kinematic variables derived from biomechanical analysis included the peak segmental angular velocities and their times of occurrence as well as the timing lags between these peaks. Angular velocities were calculated and are reported with respect to the local coordinate systems embedded in the segments. In these coordinate systems, the velocities represent the rates of flexion/extension (around the x-axis), tilting/lateral bending or radial-ulna deviation (around the y-axis) and axial rotation (around the z-axis or long axis of the segment).

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    Flexion and extension of the wrists affect the x-axis and therefore control the loft. Left wrist flexion decreases loft while left wrist extension increases loft.

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    Obviously, there is more going on than just left wrist flexion vs. left wrist extension but for the sake of simplicity let’s just look at flexion or extension. Left wrist flexion decreases effective loft whereas left wrist extension increases loft.


    Radial/Ulnar Deviation


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    Radial and Ulnar deviation occur in both wrists at the same time.

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    These movements occur in the y-axis and affect the shaft angle or plane when viewed from the target line. Above Christy is demonstrating ulnar deviation.

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    Here she is demonstrating radial deviation.


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    The difficulty with the golf swing is knowing which angle the movement is occurring in. The loss of lag at this point is due to early ulnar devation.


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    Sergio is increasing radial devation.

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    At from just prior to impact till impact, Watney shows movement toward ulnar deviation.


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    Dean Wilson shows the opposite movement toward radial deviation.


    Supination/Pronation


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    Supination and Pronation affect the z-axis or the axial rotation of the shaft. As long as there is rotation in the ulna and radial bone, there is going to be either supination or pronation occurring. From the scientific world, these are the only movements that cause axial rotation of the shaft. Left wrist supination closes the clubface while left wrist pronation opens it.


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    Here’s Gary Woodland showing left forearm supination. Notice the change in position of the logo of the glove and radial bone of left forearm. He also shows left wrist flexion.


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    Also, these two pictures of Tapio show a movement of left forearm supination although he calls it only palmar flexion and ulnar deviation, there’s more going on than he thinks. A simple cursory look at the left forearm and you can see rotation of the left ulna. The dots show this rotation or supination.


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    Qualitative Biomechanical Analysis

    Perhaps the most difficult part of qualitative biomechanical analysis for some to grasp is that one must sense the relative changes in position of a joint over time. This takes expert skill and knowledge. Quantitative biomechanical analysis has made this simpler and quantifiable as in Dr. Neal’s article shown at the beginning of this article. They just put a sensor on the left wrist and measure the x, y, z coordinate changes from one frame to the next and can calculate the amount of movement in the three planes of motion. The bottom line is while one can’t quantify movement using qualitative analysis, the data from quantitative analysis can be used to verify the movements.


    Relative movements


    In trying to understand movements, one must consider not only what position the joint is in at any instant but also how and where it is moving. So let’s take the simplest example and start to unravel this for everyone.


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    Say we’re looking at a basketball player doing a vertical jump. He flexes or bends his knees before jumping up. So at the very end of his movement to maximum flexion of his knees, he begins to extend his knees to jump. Thus, the athlete is in the process of extending his knees yet, if we didn’t know the movement was occurring, and simply looked at a still photo of his position, one would say his knees are in flexion. However, relative movement shows that he is extending. So which is it? Are we trying to define a position or a relative movement?

    For the most part, relative movement or motion analysis is more important to understand than the position at a single instant. Muscles move the limbs and joints and neural input is required to move muscles. Therefore, the brain needs to know how to fire the signals to learn a movement path. Thus the term I have been using all along is “movement toward” extension or, in the case of Hogan’s transition, supination. The muscles used in supination are already firing if the movement is toward supination. This is no different than the basketball player’s quadriceps, glutes and hamstrings all firing to extend the legs and hips to jump from the very outset of the movement. This is the key to understanding and learning.


    All or Nothing

    This brings up an important point; there are many grey areas when examining wrist and forearm movements. Just as shoulders can accelerate, decelerate and accelerate again, the movements of the wrist are just as dynamic. Just because there’s only a slight movement toward supination that never reaches the end of range of motion does not mean it does not exist. Hogan displays many movements of his left wrist and forearm that change often and rapidly. He may have extended his left wrist at the top of the backswing but flattened it slightly using flexion in transition. Also, since we can see axial rotation of the clubface, it means that supination occurred along with the flexion.

    4D system is lacking in some areas

    Truth be told, no system is perfect. The 4dswing system is better at measuring the hip/leg and shoulder movements more accurately than others. But the 4D system does not track the 6 DOF (degrees of freedom) movements of the hands.

    http://www.amm3d.com/Portals/0/artic...FullReport.pdf

    Page 72 shows graphs of the 6 degrees of freedom movements recorded by TPI 3D. If you can read graphs you’ll see that the movements are dynamic and always changing. The AMM3D/TPI3D system measures the x, y, and z coordinates of the left hand/wrist/forearm and can dissect the movements.

    Small movements like measuring lateral bend are difficult to measure using the 4D system. Small fast movements of the forearms/wrist/hands are even more difficult to measure without sensors. Could this be the reason for misinterpreting the movements?
    The hands/wrist/forearms work together to create a 360 degrees of freedom movement. In the golf swing, it is rare for movements to be only in one plane of movement. Typically they are occurring in two or all three different planes of movement concurrently and this concept seems to elude many people. Thus one must be very careful in trying to do this tedious work or risk making errors.


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    While thinking you are demonstrating only left wrist flexion, you are axially rotating the shaft. Therefore there is left forearm supination and right forearm pronation.

    As Ronald Reagan once said, “Trust but verify.”

  2. #2
    TeeAce Guest
    Quote Originally Posted by Jeff Martin View Post
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    While thinking you are demonstrating only left wrist flexion, you are axially rotating the shaft. Therefore there is left forearm supination and right forearm pronation.

    As Ronald Reagan once said, “Trust but verify.”
    Lot of right stuff there and about 4Dswing system I can tell later how I recognize some movements that are not measured from hands themselves. They all can be quite accurate seen as the relation of the club head.

    But about that photo, I know 100% sure that there is nothing else than PF in that move. It's 100% from dorsiflexion to PF and no roll at all and as far we are more or less perpendicular to the shaft by grip, it will then also rotate the shaft and close the face. So the action is pure PF and my ulna and radial are pointing exactly to the same direction in both images. No pronation, no supination.

  3. #3
    Jeff Mann Guest
    Jeffy wrote-: "While thinking you are demonstrating only left wrist flexion, you are axially rotating the shaft. Therefore there is left forearm supination and right forearm pronation."

    I agree with Tapio - there is no left forearm supination/ right forearm pronation in that demonstrated action.

    Where is there any visual evidence of the right forearm pronating in those two images?

    Jeff.

  4. #4
    TeeAce Guest
    I like the way here that we have to have evidence, and here is mine



    I hope the difference between those two movements are clear now

  5. #5
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    Quote Originally Posted by Jeff Mann View Post
    Jeffy wrote-: "While thinking you are demonstrating only left wrist flexion, you are axially rotating the shaft. Therefore there is left forearm supination and right forearm pronation."

    I agree with Tapio - there is no left forearm supination/ right forearm pronation in that demonstrated action.

    Where is there any visual evidence of the right forearm pronating in those two images?

    Jeff.
    First, Kelvin wrote it; I posted it for him.

    Second, you can't really see the right forearm, so you might as well ask "what visual evidence is there Tapio's legs don't end at the knees?"

    That said, there is indirect evidence because the clubface has closed in Tapio's demonstration, which means the forearms have rotated counter-clockwise. If Tapio had truly performed left wrist palmar flexion in isolation, the clubface would have simply delofted, as you demonstrate in this video:

    http://www.ustream.tv/recorded/20065072


    Jeff

  6. #6
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    I see a rotation of the shaft in those pics of Tapio, if it was pure P.F. the shaft would lay back without rotation. It's so simple I can't believe this! Just take the club to just below shoulder height in front and do P.F./bowing and without moving anything else in the wrists take the club to the top you will see the shaft layed back without the face rotated like Tapio did in those pics.

    Tapio you are twisting the face , anyone can see that is not pure P.F. it's a combination of P.F. and rolling the grip in your hand, Why would going from pure extention to flexion rotate the face like you show if there is no twisting/supinating/rolling?

    From a cupped lead wrist lay the shaft back and voila a bowed lead wrist with no twisting thus no affecting the face angle i.e open or closed just delofted. Then you can supinate or whatever your little heart desires.

  7. #7
    Jeff Mann Guest
    Footwedge,

    You wrote-: "I see a rotation of the shaft in those pics of Tapio, if it was pure P.F. the shaft would lay back without rotation.

    The shaft cannot lay back because of the presence of the RFFW and right palm which abuts the aft side of the grip. They prevent the club from being angularly displaced - and the club gets torqued by the fingers if he palmar flexes his left wrist when his left wrist is maximally radially deviated.

    Jeff.

  8. #8
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    Quote Originally Posted by Jeff Mann View Post
    Footwedge,

    You wrote-: "I see a rotation of the shaft in those pics of Tapio, if it was pure P.F. the shaft would lay back without rotation.

    The shaft cannot lay back because of the presence of the RFFW and right palm which abuts the aft side of the grip. They prevent the club from being angularly displaced - and the club gets torqued by the fingers if he palmar flexes his left wrist when his left wrist is maximally radially deviated.

    Jeff.

    Not if the lead wrist is in extension and the trail wrist is in flexion.

  9. #9
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    @ Tapio, In the video when you showed supination you were actually doing it with your wrist in extension.

  10. #10
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    Quote Originally Posted by Jeff Mann View Post
    Jeffy,

    You wrote-: "Second, you can't really see the right forearm, so you might as well ask "what visual evidence is there Tapio's legs don't end at the knees?"

    I disagree - I can clearly see his right forearm.

    You wrote-: "That said, there is indirect evidence because the clubface has closed in Tapio's demonstration, which means the forearms have rotated counter-clockwise."

    That is based on an "a priori" premise that only a forearm rotary motion can close the clubface. That's not true! Tapio is torquing the clubshaft around its longitudinal axis with his fingers - when he palmar flexes his left wrist.

    You also wrote-: "If Tapio had truly performed left wrist palmar flexion in isolation, the clubface would have simply delofted, as you demonstrate in this video:

    http://www.ustream.tv/recorded/20065072"

    There is a major difference between my demonstration and Tapio's demonstration. Tapio has his left wrist radially deviated, and the clubshaft is at a 90 degree angle relative to the left arm. In my demonstration, I have my left wrist neutral (significantly ulnar-deviated relative to Tapio's demonstration) and the clubshaft is nearly in a straight line relationship with the left forearm (other than the amount reflecting the accumulator #3 angle). Under those conditions, left wrist palmar flexion would cause the clubshaft to be displaced angularly (relative to the left arm) with no torquing of the clubshaft around its longitudinal axis.

    Jeff.

    OK. No "black is white" bullshit here or opinions about what Tapio is doing with his fingers that you can't even see. Cut it out or we'll have to say goodbye.


    Jeff

  11. #11
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    Quote Originally Posted by footwedge View Post
    I see a rotation of the shaft in those pics of Tapio, if it was pure P.F. the shaft would lay back without rotation. It's so simple I can't believe this! Just take the club to just below shoulder height in front and do P.F./bowing and without moving anything else in the wrists take the club to the top you will see the shaft layed back without the face rotated like Tapio did in those pics.

    Tapio you are twisting the face , anyone can see that is not pure P.F. it's a combination of P.F. and rolling the grip in your hand, Why would going from pure extention to flexion rotate the face like you show if there is no twisting/supinating/rolling?

    From a cupped lead wrist lay the shaft back and voila a bowed lead wrist with no twisting thus no affecting the face angle i.e open or closed just delofted. Then you can supinate or whatever your little heart desires.
    Do you mean like this?

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    Jeff

  12. #12
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    Quote Originally Posted by Jeff Mann View Post
    Footwedge,

    You wrote-: "I see a rotation of the shaft in those pics of Tapio, if it was pure P.F. the shaft would lay back without rotation.

    The shaft cannot lay back because of the presence of the RFFW and right palm which abuts the aft side of the grip. They prevent the club from being angularly displaced - and the club gets torqued by the fingers if he palmar flexes his left wrist when his left wrist is maximally radially deviated.

    Jeff.
    That's if you think everyone does things your way.

  13. #13
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    Quote Originally Posted by Jeff Martin View Post
    Do you mean like this?

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    Jeff

    No not quite, keep the clubshaft up just below shoulder height with a cupped lead wrist and then just lay the shaft back till the trail wrist bends back, it's only a wrist movement.

  14. #14
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    Quote Originally Posted by footwedge View Post
    No not quite, keep the clubshaft up just below shoulder height with a cupped lead wrist and then just lay the shaft back till the trail wrist bends back, it's only a wrist movement.
    I thought I was only making a wrist movement...


    Jeff

  15. #15
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    Quote Originally Posted by Jeff Martin View Post
    I thought I was only making a wrist movement...


    Jeff


    You might be but the shaft will be up higher and in a steeper position more like Fred Couples.

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