I've done 2 full Iron man distance triathlons and dozens of shorter ones, raced road bikes, and run marathons which all included wt. training ......however;

I just recently started training at a Cross Fit gym and the workouts are harder than anything I've done. The work out is a blend of cardio, and pure strength/explosive power. The super low tech workouts can be done just about anywhere and change each day. In six weeks, I haven't done the same workout twice. I find the workout routines more of challenge than Marine Corps boot camp (although it HAS been a while).

I know it sounds like a mix between a trendy new workout and fight club, but results (and challenge) speak for themselves.

Check it out: Welcome to CrossFit: Forging Elite Fitness