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More Surprising Findings from the World of Biomechanical Analysis!

This is part II of the summary I began last week (located here). Today’s discussion has important implications for how we instruct new players in learning to a forehand.

In case you’re just joining us, I’m reviewing an article published in Sports Biomechanics called “Biomechanical analysis of the sidearm throwing motion for distance of a flying disc: a comparison of skilled and unskilled players.” (Being a scientist, I should make it clear that my analysis of the work reported is very similar to, but not exactly the same as the conclusions arrived at by the authors of the paper. So this is not a direct summary of the paper.)

In this study ten skilled and seven unskilled players were taped throwing forehands as far as they could. The angles of the shoulder, elbow, and wrist were analyzed. The initial velocity of the discs, spin rate of the discs, all angles of the disc, and distance of the throws were measured. The skilled groups produced throws around 50 meters while the unskilled group produced throws around 30 meters.

The main point of last week was that of all the things measured about the disc, the only things that differed were the angle of attack of the disc at release, and the spin rate of the disc at release. The velocity and everything else about the disc were essentially the same for both groups.

Last week I briefly discussed the angle of attack of the disc. This week I am going to talk about the spin rate of the disc. Specifically what were the more experienced players doing differently to produce the greater spin rate?
You will not be surprised to hear that it is, in fact, all in the wrist. You may be surprised to find out what the wrist is actually doing.

First we have to use words to describe some human motion. If you can hang through these next three paragraphs, you’ll understand the rest okay. Put your hand out as if you were going to shake someone else’s hand. Now freeze your elbow and pretend you are shaking their hand using just your wrist. When your pinky is going toward the floor, that’s called “ulnar deviation” and that’s what you do as you’re about to release a forehand. When your thumb is moving up that’s called “radial deviation” and that’s what you do prior to ulnar deviation when throwing a forehand. We’ll call all of this the “hand shaking” motion for short.

Now put your hand out as if you were holding a pie. Freeze your elbow and pretend you are flipping the pie into your own face. Yum! What your wrist is doing is palmar flexion. When you are throwing a forehand, do you think you are doing more hand shaking or more pie flipping? How would you expect the skilled vs. unskilled players to differ in their hand shaking vs. pie flipping motions?

Last one: you are holding the pie again. This means your forearm is in the supinated position. Now turn your hand over to drop the pie directly on the ground. You are pronating your forearm.

What is most surprising about the motion analysis is that there was rapid pronation occurring in the forearms of the skilled throwers just before release of the disc. The magnitude of pronation was small (about 6 degrees) but it’s effect is large. The unskilled throwers were actually in the act of rapidly supinating their forearms at the time of release. So there are diametrically opposed difference in motion between the skilled and unskilled throwers. This motion is occurring about 0.016 seconds before the release of the disc.

So what? This slight pronation of the forearm allows the palmar flexion (pie flipping) motion to add forward velocity to the disc. (without pronation, the pie flipping motion would put the pie/disc in your face). The pie flipping motion is definitely important in imparting spin to the disc. Skilled players moved 22 degrees of pie flipping vs. only 13 degrees of hand shaking. Unskilled players actually used 41 degrees of pie flipping motion but the forearm wasn’t oriented correctly. (They used 11 degrees of hand shaking.)

What does this mean for your practice and for your instruction? Well, these skilled players had played 2-4 years. I’d say chances are if you are an intermediate level thrower, your wrist has already figured it out. But there may be some implications for how we teach others.

Theory 1: A traditional way of teaching new players is to tell them to put their forearms in the supinated position and keep them there. From this position, the “flick” of the disc is generated only by the hand shaking motion. But we really want them to learn to use the pie flipping motion as well. That is where the speed (and spin generation) of the flick really comes from. Perhaps less instruction is better and players should just be told to start with the forearm in the supinated position and keep the disc in the same plane as they throw. Or, it may be useful to use an actual baseball in explanation because a baseball cannot be thrown sidearm without pronating the forearm.

Theory 2: The problems for unskilled throwers may be beginning a whole 0.1 seconds before releasing the disc. The wrist motions described were the most divergent motions between the skilled and unskilled groups but there were differences in shoulder motion as well. Fortunately, one of these problems is an easy fix. If you stand with your hands hanging by your side and then with your elbows and wrists frozen, raise your arms- that is called abduction. The angle created by the line of the elbow and the line of the torso were measured for both groups. For skilled players this angle remained constant throughout the throwing motion at very nearly 60 degrees. For the unskilled throwers, this angle fluctuated by about twenty degrees throughout the throwing motion. The pattern was large to small to large angle in a kind of swoopy motion. This motion at the shoulder joint is what allows for easy supinating of the forearms as the disc is realeased. But remember this is the opposite of the motion we want! So, eliminate the swoop, eliminate the supination, increase the effectiveness of pie flipping in spin generation. This, I think, is the better of the two theories.

Please try these out on all your friends and let me know what works!

I hope that this article summary has been helpful. At the very least, I hope that you now have a better understanding of what is actually occurring (or should be) while you are throwing your forehands. I hope that you also have gained an appreciation for the utility of biomechanical analysis.

As I find more articles or as more are published, I’ll be attempting to translate them from kinesio-speak to English right here!

See you on the field!
Melissa Witmer

6 thoughts on “More Surprising Findings from the World of Biomechanical Analysis!”

  1. Hey Melissa, great follow up on your previous research. From your story I would deduce that for the hand motion it would be best to not teach it, since people will learn automatically. It is such a tiny difference time-wise that it would be hard to explain anyway, since you can't really show someone or see them doing it wrong (if I envision it correctly).

    As for the swoop, that is one to focus on. It is something I did when I was just starting because I was used to tennis motions. I see many junior players doing this in their throws. Usually I will told my hands out and let them keep the disc above it throughout the throw to make them see what they are doing.

    Thanks for sharing your findings and keep up the good work!

  2. Thanks Jesse,
    I like the idea of using props (or your hands) to guide the thrower's motion and provide instant feedback. You'll see from my next post (coming soon!) that you've got the right idea as far as teaching strategy. It is better to have the players focus on something external (like avoiding your hands) rather than internal (like trying to control their own swoop. : )

  3. Something I've been thinking of for a while (and discussed with you Melissa last week) was how golf pros teach golfers using a swing motion program that helps analyze their swing in real time. I've thought it would be something cool to use for teaching people to throw as well because you could much more easily breakdown the throw and teach people the mechanics of the throw.

  4. I just found this post and am floored that there’s been actual research into forehand motion. Until now it had never occurred to me that palmer flexion might be a legitimate or good way to put spin on a forehand.

    Is there similar research for the backhand?

  5. Ben,
    Yea this lab had quite an impressive experimental setup. Really nice graphs of all of the joint angles over time and everything. After reading this paper I actually taught myself to throw a very nice high release forehand by changing my grip slightly to allow more palmer flexion to occur. It’s not quite game ready and not a throw I’d recommend spending a lot of time on, but it is definitely interesting that I got an almost immediately usable new throw after reading this paper.

    Unfortunately, I have not seen similar research for the backhand.

    Thanks for reading!

  6. Hey Melissa!

    I understand the most of the explications on this page, but I didn’t understand what’s wrong with the hands shaking? I mean, this is really how beginners throw I remarked that one coaching cue I constantly heard about is “use your wrist when you flick the disc” or something like that.

    And… You mean that we need to use the flipping the pie… I don’t really understand well how to transfer it to a throwing mechanics… I mean… By your explanation I refer myself to the flick throw mechanics Rowan McDonnell show in one of his video. He take the disc, do an abduction with his forearm (at this moment, the disc is up ready to throw like an archer who is ready to shoot, and the forearm face down in a ~45 degrees), so his wrist is in a pronation position (the pie is going down) and when he throw he place his wrist in a supination to proantion position. I tried to figure out the entire throwing mechanics.

    He explain here how to do this at home (to practice the motion) :

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