The biomechanics of twisting somersaults has always been an interesting subject to me. I am currently coaching Trampoline and Tumbling, and my daughter Jenny is one of my athletes, (Air Sports Unlimited, Scottsdale, Arizona). Quite often I can’t resist doing something myself. Last weekend I watched one of my gymnasts try a Rudi (1 1/2 twist front somersault) into the pit. She was having trouble so I mentioned to her how all she needed to do was rapidly drop one arm sideways. On a front somersault if you twist left then drop your right arm, if you twist right then drop your left arm, (the opposite for back somersaults). Of course your body needs to be as tight and straight as possible; any looseness will probably inhibit the twist. I thought that it would be a good time to demonstrate and have some fun myself. So I first did my normal twist direction. Then I thought, if it is so easy I should be able to twist in my “non-normal” direction by following my own advice. So I attempted a trick that I had never tried before, ever; a Rudi in my opposite direction! The result; well check out the attached video. It seems you can teach an old dog new tricks! See if you can figure out which is my normal direction and which was the one that I did for the first time that day.
Here’s a technical description: When you start your somersault you have a certain amount of angular momentum gained from the way you take off; once in the air momentum is conserved. You can however transfer momentum from the somersaulting axis to the twisting axis by causing a slight tilt sideways. You do this by quickly dropping an arm sideways. Dropping your right arm tilts you to the left causing some angular momentum to be transferred to the twist axis, resulting in a twist to the left. If you were able to exactly move your arms back then the twist would instantly stop. If you carefully look at the two videos you will see that each leans lightly to different sides. Also you can easily tell the direction of twist; if you see my stomach after take off then I am twisting left, and have dropped my right arm. And visa-versa on the other side.
Let me know which you think is the one I had never done before that day, (the video was the second one I did), and I didn’t even hurt myself!