Increase the rebound slows the return. And if excessive can cause the pumping down effect which will alter the geometry. Too little rebound will unsettle the bike over bumps and can cause tyre wear and traction issues as the tyre unloads. (See the video clip).
A little fitness helps if your going to spend money to go abroad, I've tried to never missed a session. But after several days on track and you have blisters on your feet as well as your hands You just need to man up and get out there !