Maya - Arms don't take straight path between keyframes

erebel55

I have built my own skeleton in Maya 2016 and am attempting to make basic animations so that I can test the skin weights.

However, I am running into an issue that I can't make any sense of.

The arms are set to rotate straight forward and back, but instead they are taking there own path and doing a swinging motion.

Here is a video of what it looks like (youtube)
http://youtu.be/tOqT1PmD8QE

Any help is appreciated. Thank you

a3D

Google gimbal lock

erebel55

Thank you so much, that is exactly what's going on. I searched for so long but didn't know what it was called. Thank you for the keyword!