The naulitus machines allow you to work out many , many parts of your body without requiring much power from your elbows to your hands, thus u can take it easy on the tennis elbow
problem. Any exercises not requiring much grip strength you can do--abs, shoulders, pecs, neck, back, quads, calfs/hemstrings--u name it.
Consult with a trainer if u need help. Consult doc for elbow problem. Good luck.