Why doesn't my butt hurt?

On Monday night I did a muscle toning class at the gym. Tuesday morning I felt like someone had taken a hammer to my butt - I thought for sure I would see bruises - that's how much I hurt. Wednesday I felt mildly better but decided I'd try another of these muscle toning classes. It was with a different teacher and was at a more advanced level. It was a great class - it challenged me and a couple of times I didn't think I'd be able to do the whole set of repetitions. But I made it through and was quite proud of myself. This morning I expected to have a repeat of Tuesday morning's soreness but I don't. In fact the stiffness from yesterday is completely gone. Dare I say it? I feel good. Huh.