Tire Flips

Tire Flips + plyo jumps (in and out of tire) 50 yards= 1 set
3 sets
Slosh pipe OH carries.
Sledgehammer swings, a few sets two arm, one-arm, etc.

Simple, but not easy.
There's my cardio. You can keep your 45 minutes on the elliptical, and you can keep your "fat burning zone."