Copy and Paste animation

I have a character running. I duplicate the characters rig and make changes. I decide I want to copy and paste the animation from the first rig to the duplicated rig. Is this possible? So far I have had to copy the LocRot of all the bones for each frame and paste it over to the second rig one frame at a time (which takes a very long time). Does anyone know if this is possible? Thank you.

Check out the NLA.

in the dopesheet, select all keys, press CTL-C

switch to new armature, in the dopesheet, press CTL-V

Make sure same bones are selected between armatures