I just joined a gym this weekend. It's not a gym where you sit around, watching TV, and you keep thinking, "Man, I should go to the gym." Not only do you have to go online and make appointments, but the whole thing is personal training (small group level). For 25 minutes, you're running around, doing all these exercises that the trainer has you do. It's always different, and you'll work every muscle. You're going fast enough, from exercise to exercise, that you don't stop and rest much. So the workout is far more aerobic than, say, lifting weights normally is.
And then you spend 25 minutes on a cardio machine.
Saturday was my first day, so they didn't have me do the 25 minutes of cardio at the end. I did stuff like reverse lunges and jumping jacks and curls, among way more stuff.
Well, my thighs have never been this sore. Walking up and down steps? It's not okay. And my lower, lower abs are sore, so yesterday, if I was lying on the couch and had to get up to, say, pee, it would HURT to sit up.
Tonight, I'm doing it all. Over. Again.