It's probably because your not stretching before hand.
And your using muscles you don't usually use.
I know it sounds funny, because how many people do you see stretching before
a dance routine? Probably none, but they're probably used to it.
A good warm up 1st is key, then stretch afterwards too.
These days all I do is walk, I like it though.
I used to go to the gym regularly, the treadmill and rowing machine were my favourite.
Then onto the weights. I really loved it...
Don't get me wrong, I wasn't super fit, or muscular, just toned with definition.
I'd love to go back, but these days I'm far too knackered....lol