Watch your position n the spin 'bike', if they are like the ones I use, you can only get a close fit, and it's easy to try to do too much and have a poor fit. I used to get back pain, then spasms(try those for a good time), untill I realised if I didn't try to do jumps, I didn't get pain. Plus, they aren't anything I'd do on a real bike, so why do them on a spin bike?