Don't do gymnastics if the idea is to stay fit. That's my opinion. Only because you will forgo seeing the results for some time, until you learn enough skill to pull it off. Kick boxing is a big yes. I took up kick boxing for a couple of years for strength and fitness, and saw results right away. But it also pumped me up a little too much adrenaline-wise for some reason, and I gave it up. I was full of piss and wind back then, so I couldn't afford to be engaging in sport that made me feel like a badass! lol