I tried spin classes in the early Fall. I can definitely see that they are a great workout, but I stopped going b/c (a) the offerings at my gym mostly didn't jibe with my schedule and (b) there's no digital setting to the resistance on the spin bikes. The latter may sound trivial, but I really couldn't quite get used to not knowing if I was feeling much better than the day before or if my resistance setting was just easier. So I've been using the stationary bicycles on my own. It doesn't have the benefit of group/leader encouragement, but I'm pretty good at pushing myself. Every 3-4 weeks I go up one digital level on the interval routines. 50 minutes is all I can stand, though. After that, the combination of exhaustion and boredom sends me to the showers.