Personally, I don't really believe in working out certain muscles for musical-based goals. The best thing to get better at something is to practice it. Why lift weights or jog extra miles while you could spend that time on your kit?
BUT.. that doesnt mean that I`m not a believer in feeling good in (or with) your body. Being in a good shape will never hurt your playing. And ofcourse, 'being in good shape' differs from person to person and being in a good physical form will probably add to your stamina, feel and confidence...
...Altough a guy like Gene Hoglan is very far away from being a sporty kinda guy and he seems to be able to play insane stuff.
I struggle with exercising when the kit is calling; I tell myself, "Do you want to be buff or do you want to be a better drummer?" Of course the answer is the latter.
But...
Last summer I threw my back out while packing up gear, and couldn't make the show. I had lost all balance in my practice to exercise ratio, and my body was letting me know it felt neglected. I still don't exercise enough (drumming is much more fun

) but I at least stretch do a half-hour stretching routine 3-4 times a week and do light weight workouts 2-3 times a week.
Once this Wisconsin marathon of a winter ends, I'll probably start hitting the bike trails again, too.