discovering the human body

[gusl]

I was just showing off to shaktool how make the tendons in my arm bulge: switching my 3rd and 4th fingers has the biggest effect. He showed me an even better trick.

Stand up. Grab the left end of the desk with your left arm. Now rotate your elbow. (I was amazed at how much I could rotate it (~100 deg). Now rotate the elbow clockwise, all the way.

I can bring my hand back to neutral position while keeping the elbow there. But I can't put the elbow there in the first place without turning my hand (or hold it somewhere). So once I let go, I can't reverse the motion.

My arms have ridiculously many degrees of freedom: there's turning at the elbows (~160 deg, shoulders fixed) and wrists (~ 135 deg, elbows fixed). The hands themselves seem to have no rotation when the wrists are fixed.

When I interviewed with ITA last year, a former roboticist showed me that if you are holding a glass, you need to rotate your hands 720 degrees to get back to the same position (assuming you don't want to spill it). There was another trick thing about muscles and non-reversible motions.

Comments

[altamira16.livejournal.com]

The elbow rotation thing is a warm up exercise that we use for trapeze.