Squircle and the Kettlebell Snatch
My favorite applied math blogger just revisited a topic that I had forgotten about: the squircle - a shape between the circle and the square.
You see them everyday when you look at the icons on your iPhone. The squircle is not a square with rounded corners, the curvature of the squircle is continuous...so that's kind of cool - nature abhors a discontinuity, shapes like these can describe physical movement nicely.
This is the shape that I've had in my mind, but never really put to words when I'm describing the difference between a swing and a snatch, and the difference between a snatch and a heavy snatch.
The arc that a swing makes is pretty much circular.
But you need to "tame the arc" for a snatch or a clean. That is, you need to bring the bell up more straight along your body - "like zipping a coat". I've noticed that there's also a bit of a flattening of the back swing too, I would say that the arc that you make when you snatch looks more like this.
As you snatch a heavier and heavier weight, you need to keep the bell in closer. If the bell gets too far away from you, it will pull you over on your face. As the snatch approaches 1/2 body weight, you really need to keep it close no matter how strong you are. As the bell gets heavier, you also need to get more momentum into the bell at the bottom of the arc when your hips have the most mechanical advantage. You need to square your squircle even more...which is a flattening of the back swing and a flattening of the arc in front of your body. That also requires a tighter corner (and hence much more power) at the transition.
I know Randy's refreshing a "Dynamics of the Swing" blog post that we worked on over a decade ago. So I won't steal his thunder. But the force you put into the bell (and how "heavy the bell feels") is proportional to the curvature of it's path. So a swing is much more constant force, where as a snatch is more pulsed at the extremes.
All plots courtesy of IDL - we invented the idea of Python before Python ever existed.