Science Experiment Directions: Involuntary Muscle Movement

Floating Arms

The Set Up

Have your child stand in a doorway with their arms touching each side.  Then have them press into the doorframe as hard as they can for about a minute.  (This one might be tough for younger children if they don’t quite get staying still and pressing hard for that long, but older children can experience this.)  After a minute has passed have them step forward out of the doorway and watch their arms mysteriously float up.

The Science

Why do your arms float on their own?  This is known as the Kohnstamm phenomenon. It is an involuntary contraction of the muscles after a prolonged voluntary contraction.  Basically, you are choosing to press your arms against the doorway, this is the voluntary contraction.  Once you step away your muscles maintain the contraction even though you have stopped trying to push.  This is the involuntary contraction.  You can repress this floating reaction by pressing your arms tightly to your side.