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Surprising Findings From the World of Biomechanical Analysis!

I am going to attempt a summary of 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.” I am hoping to offer something brief, easily understood, and practical. If you want experimental details, or are looking for something more erudite, please read the paper : )

In this study ten skilled and seven unskilled players were taped throwing forehands as far as they could. The movements of their shoulders, arms, 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. Can you guess the cause of this difference? Were the skilled players able to put more force into the disc and release it at a higher velocity? Could they put more spin on it? Or was it a combination of velocity and spin rate? Some other factor like releasing the disc with inside-out angle?

One of the surprising results (to me anyway) of this study is that the velocity of the disc at release was the same for skilled and unskilled throwers. All of the test subjects were physically active Japanese males between around the age of twenty-five. It’s probably fair to say they can all throw a baseball (a standard projectile) reasonably well. Somewhat surprisingly, prior studies by this research group show that throwing a baseball overhand and throwing a forehand are biomechanically similar. This just highlights what we already know- that throwing a disc is different than throwing a standard projectile. Still I would not have expected the initial velocity for both groups to be totally the same.

There were only two factors about the disc at release that differed significantly between the two groups. The first factor was the spin rate. The average spin rate (in rounds per second) for the skilled throwers (12.9 rps) was 3.2 rps more than the average spin rate for unskilled throwers (9.7rps).

The second factor was the angle of attack. A slightly positive angle of attack generates more lift for the disc. Having zero angle of attack generates the least amount of drag. (Explanation of angle of attack: Angle of attack is the angle between the plane of the disc and the vector of velocity. So, if you lay a disc flat on a table and slide it across the table, the disc plane and the velocity vector are parallel. Angle of attack equals zero. But if you place a book under the front rim of the disc and slide it forward, there will be a positive angle of attack.) The angle of attack for the trials of the skilled thowers averaged 0.2 degrees and varied from -1.1 to +1.3 degrees. The angle of attack for unskilled players averaged 1.0 degrees and varied from -2.6 to 4.6 degrees. It would appear that having less drag on the disc at release is important so that drag is minimized and velocity is maintained.

So, which one of these two factors, spin rate or angle of attack, is most important to master in order to gain the most distance on your throws? …the answer is… I have no idea. (I was the one surprised by the velocity thing, remember?) Anyway, let’s be practical. The maximum variation in attack angle in this study was 7.2 degrees. If you are throwing a disc at any velocity, do you think you will know when your angle of attack is off by 5 degrees? Good luck! In truth, you will figure out how to do the angle of attack correctly with practice. You will be seeking the minimal amount of drag approaching your release point and your body will learn how to do this for you. I cannot imagine that this is something you can work on at the level of cognition unless your angles of attack are very far off. If you can throw an air bounce backhand, what you are seeking is the absence of how that feels. An air bounce purposefully has a large difference between the velocity vector and the plane of the disc. It slows down because of the increase in drag, and it lifts (the bounce part) because of the increase in lift generated by the larger positive angle of attack. As a word of caution, can be difficult for players to know when they are throwing air bounce. Because you do NOT want air bounce on most of your throws, I would recommend learning to throw an air bounce only after you have a certain competency with your regular backhand. If you become competent at creating a throw with extra drag (the air bounce) first, I believe your body will have a more difficult time feeling its way toward the optimal minimal drag creating angle.

All that is to say, that deliberately working on increasing your spin on the disc may be the easier way to go. And how do we generate spin on the disc? And how do we help new players get the whole spin thing? In my next installment I’ll discuss more surprising findings! Sorry to keep you in suspense.

Or you can just read the paper yourself:

Sasakawa, K. and Sakurai, S. (2008). Biomechanical analysis of the sidearm throwing motion for distance of a flying disc: A comparison of skilled and unskilled Ultimate players. Sports Biomechanics, 7(3), 311-321.

See you on the field!
Melissa Witmer

8 thoughts on “Surprising Findings From the World of Biomechanical Analysis!”

  1. Very interesting, I wouldn't have guessed that unskilled players would be throwing at the same starting velocity either. The spin of the disc is also a factor that I would have thought to be bigger.

    The angle being something that your body learns is an interesting result of your study. I always tell people to keep their release as level as possible, so that seems the right way to tell them. Of course, this is hard for people to 'feel' immediately, which is perfectly shown by your study because the differences are so small there.

    Great study, and I'm looking forward to the next one!

  2. Thanks Jesse!

    I just want to clarify a minor detail… The idea that the angle is something that your body learns is just my opinion, not necessarily a conclusion of the researchers in the study. It's hard to say from the study what exactly the unskilled throwers were doing. They give an average and a standard deviation for the seven trials. Some of them very well may have been throwing at the correct release angle. Also, all of the measurements for skilled throwers had smaller deviations than for the unskilled group.

    But yes, the research does show that the skilled players ten trials had a much smaller deviation and they appear to be converging on zero angle. So, instructing palyers to keep it level is definitely the way to go.

    Thanks for your input and thanks for reading!

  3. You’re exactly right about the airbounce. I learned to throw an airbounce backhand before I had fully mastered a regular backhand. When I started playing more and trying longer backhand hucks, those throws were absolutely terrible. The airbounce qualities of lift and float were extraordinarily pronounced in longer throws. It took several weeks to correct that. As a result, I flat out refuse to teach the airbounce throw to newer players, no matter how cool they think it looks.

    1.  @pkenworthy I’ve been dealing with this ever since I learned how to throw it. Watching new players to the sport loving the air bounce because they thought it looked cool. It’s actually a really simple fix – just roll your wrist forward which forces the disc to flatten out and it will naturally help someone throw the disc on a more even plane. I struggled for a whole summer trying to unlearn the air bounce but it’s a good accessory throw to have – and useful in other disc sports (like freestyle)

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