Tuesday, December 23, 2014

A Kinematic Chain is You

Ignore the caboodle. 
First, if you don't like the deep end of technique discussion - stop here. This one is going deep. I am shooting to keep it readable, but this is stuff that I've talked about with a number of folks over a few different places and I wanted to get this out there.

A kinematic chain is something that gets talked about quite a bit in sports like tennis and ball-golf, where quite frankly there's big money and coaches who put their lives into improving the form of the best players in the world.

A kinematic chain is simply put - rigid bodies connected by joints. We could get very technical here, but I want this to be readable - so I'm going to try to keep this friendly enough that I could understand it (which is to say that a dim witted caveman could understand it).

The degrees of freedom (mobility) of the chain impose constraints on the system. The easy way to think of that, is that our joints (knees, hips, shoulders, elbows) all have a certain amount of flexibility and that effects how we throw a disc. We can bend to a point, then we have to stop because it doesn't bend anymore!

The first thing that is important to cover is how our body (our kinematic chain) is connected to the ground. Pushing off the ground is the first element of any motion. If you were standing on a slick ice rink, it would be nearly impossible to drive a disc in any powerful way. We're typically connected via a better surface than ice, so we have to take advantage of that by being smart.

The way the feet connect to the ground is critical for two reasons: first, because it's going to drive the force of your shot and second, it's going to transfer the force through your knee, starting the chain reaction of force. If you are setting your feet on the ground in a bad way - you might be able to get good force, but you can't transfer any of it into your knee! You may be able to put all the force into the knee, but not be able to generate enough force to be useful. You can see, it's gotta happen right!

Pretty similar? The kinematic chain in action.


Tennis is almost all torsion and less lateral movement because they have much less time to react, but it's a very similar kinematic chain. Disc golf's backhand is much more a combination lateral shifting that terminates in rotation. Because we have the time and space to setup our chain, we can get some huge force going.

The back foot can transfer weight two common ways:

1. You can get up on the ball of your foot with the heel off the ground. I prefer this and it's like a boxer driving a punch. (Paul McBeth does this quite often)
2. You can plant the foot flatter, and rock through the instep like a pitcher coming off a mound. (Feldberg is doing that above)

In both cases, you want to see your back foot leaving the ground heel first, not toes first. If your toes are leaving the ground before your heel, then you're not going to get the best weight shift and torsion that you can.

A very common issue is having your back foot's toes pointed too far backwards which stops any real transfer of power from the foot into the knee. We call this getting horse stanced (like you're sitting on a horse with your feet spread wide) and while it's very balanced, it's terrible for initiating the uncoiling of the torsion you create.

Torsion is the product of twisting our upper body against our lower body in the back-swing. Creating and unloading torsion is a huge part of the power generation of both a forehand and a backhand.

There's a feature of our biology as humans that is a big part of the backhand. A back-swing can twist our upper body to a physical constraint. We only have so much freedom of movement before our hips stop our upper body from turning anymore.

When you hit that constraint, the spring of your upper body is fully loaded. This is why it's so important to time your back-swing so that you're not reaching back before you're ready to use that torsion. 

As soon as you are hitting the limit of your back-swing, you want it to reverse and start coming back the other way. Reach back too early and leave the upper body sitting for a bit,  and everything relaxes.  The last thing you want is your muscles decide to chill out for a bit instead of remaining taught and explosive! Think of all the other sport motions that utilize a constraint to bounce back from: Baseball hitters, baseball pitchers, football quarterbacks, hockey shots, tennis shots... the list is long. 

When it's timed right, you're coiling to the constraint of your mobility - then immediately uncoiling as the plant foot is pushing back against the weight of your forward momentum. That combo is so forceful that your arm's job becomes to simply hold onto the disc, bringing it through the elbow extension.

It's something I reiterate all the time: there's no throwing the disc hard*. Throwing it hard implies that you're using arm muscle to try to force the disc forward. Once you've felt the power of torsion and a solid plant, there's a couple things that you notice: it's almost effortless and the disc will feel like it's violently ejecting from your hand.

The motion is going to happen so fast, that any idea of putting any real force into the extension of the forearm is pretty absurd.

* I definitely hesitate to get into the following, because it's hard to know what forces are truly greater - but it does seem like a powerful uncorking of the back swing is more powerful than the force of the brace. I know a number of guys who are throwing some big distance from the one-step and it's clear that the power is all rotation. I'm not saying that you don't need to brace, I'm saying that for distance over accuracy you can amplify the torsion by increasing the depth of the back swing and delaying it a bit so that the action has to happen faster. So you can probably get away with saying "uncork hard".

And since we're talking about crazy stuff, let's look at the following graph: (original thread here)


What it shows is that as the disc speed out of your hand increases - the RPMs of the disc itself DECREASES at a pretty specific speed. As you start really getting big hand speed (55mph+) things change a bit around the wrist and the ejection of the disc. I have had many conversations about this with people, but it was always conjecture. This was the first time I saw actual data on where the physical action of a throw changes. Higher speed distance shots, it appears to me, are more influenced by hand speed than the levering action of the disc out of the hit.

So most likely there's a good chunk of distance that is frustratingly, a wash. You can increase hand speed, decrease the spin of the disc, and end up with a shorter shot because the disc will be less stable. There's slower hand speeds, with higher spin, that will travel farther going slower because the spin rate is higher.... BUT (UHG!!!) there's also not any very high speed releases that have high spin rates.

What actually imparts spin on the disc, is the disc being held later into the hit. Once the hand speed is really high, it becomes really hard to hold the disc late enough to impart that same spin levels.

Just kill me now. I'm gonna be in the back yard putting.,. (slams door).... Okay, I'm back.

You can also increase the hand speed by coming into the right pec with more hand speed, assuming you can tolerate the force and truly hold through the hit - but the extension is where the forces multiply. The very VERY last bit you are holding the disc, is ultimately the most important for imparting acceleration with spin that will stabilize your disc.

It's the biggest reason of why your grip is so important. The violence of the redirection of your hand around the nose of the disc is going to be substantial. I've stopped squeezing the rim with my index finger in my power grip, instead focusing on keeping it in a very hook-like hold with my thumb. That way when the initial fingers blow off the rim, I still have some extra pull on the rim. 

Lastly, this kinetic chain is very dependent on something that I may never live down: staying loose.




6 comments:

  1. HUB:

    Love your posts but wish you would spell 'heel' properly, just once. Please? I'm begging you.

    Heel: part of your foot
    Heal: recovery from injury

    It's one measly little letter. I've been biting my tongue on this one for months but I can't take it any more!

    :^)

    ~C

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    1. Fixed! Yeah, I get that one wrong every single time. I don't know why, but that word looks much better HEAL than HEEL... bad brain.

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  2. Would simply improving your grip strength increase RPM, therefore increasing distance?

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    1. I think it is possible to get better results with a stronger grip, but I also think that the wrist gets more rigid as things speed up because you just can't load and unload fast enough to be effective before the release.

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  3. This is very much like teaching rotational hitting it baseball.

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  4. What is this thumb hook you are referring to in the last paragraph as opposed to the pressure of the thumb? You lost me on that point. Great article though. Keep it up!

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