Tennis
Venus and Serena, look out! I've started playing tennis again after recovering from tennis elbow surgery and all I can say is...wow. I'm hitting better than I ever have in my life! And no, the doctor didn't implant some super-bionic device to ensure smokers and aces. Hell, I'd save that procedure for my brain, not an appendage! I think...no, I KNOW my improvement is a result of the Interactive Metronome sessions I've done. My inner timer is so precise, I'm waiting any minute (or millisecond) for a call from those nice folks at Greenwich asking me to be the timing standard for their atomic clock. So if you want your game, whatever it is, to reach the next level, try a 15 session course of IM. But if you do, don't challenge me to a game. My baseline was probably a lot worse than yours.