Kettlebells are wild. Do 100 swings, feel like you could have done 500, all good.
Wake up the next day, step out of bed, and...
Collapse. Dear god how are my legs this sore?
I was really into them for awhile a few years back. It does get easier after a few days as you acclimate. I got up to a 2 pood (72 lb) bell at one point before my schedule got whack. People at work at the restaurant I was at used to run at me for fun just to try to get me off balance due to how solid my core got. Wouldn't even spill stuff on my tray when they did.
Those first few days though are brutal.