I've been in Shotokan a year or so now (see my member title) and am a fresh, new, purple belt. There's still so much more improvement I need to work on. I've been doing a lot of running on treadmill (and on the road), situps, pullups, and freeweights.

What are the best muscles to train to get faster, harder punching strength and how would one go about this? I've noticed also since I've been running my Sensei says my footwork in kata looks much better.

I'm also open to what other styles teach because I am interested in going far beyond Karate in the near future so please feel free to tell me your own style's methods or personal methods.