Dana:
Sorry about the coffee and also the sore back. Offering you a clean towel to wipe up.
It isn't surprising..all that banging and slamming up and down you were doing. The key is all in the legs and thighs. More muscle control there ...it feels comforting and shows who is control when your thighs and legs are pressing firmly.
Also keeping your upper body more relaxed, moving with the motion, becoming one fluid movement...It is less jarring on the back that way, but when you are really going for it, the slamming is inevitable. Don't worry now that you are starting to do it daily, it will get better.
I was going to suggest asking Tracy for advice, but now that she is married she probably doesn't have the time, nor the desire to do it very often. {{Shrug}}} that happens sometimes.
Kismet