Our body is a fascinating machine, and is far more complex than we imagine.
Hold your hand in front of you, palm up and fingers splayed.
Now bend your fingers at their first joint past the knuckles. Your hand should look a bit like a spider on its back, curling up its legs — that’s your proximal interphalangeal joints (PIJs) bending.
Let your hand splay out again. This time, curl just your pointer finger and let it uncurl. Now do your ring finger.
What do you think is going on here? If you had to guess, where would you say the muscle involved is?
This video (of unknown origin) which we saw Tweeted by the account How Things Work, illustrates the effect using a cadaver limb:
Sit back and watch:
This is how you flex your fingers pic.twitter.com/BACT0bub5q
— How Things Work (@ThingsWork) February 16, 2017