"These are best done on an old tractor tire (laying on its side) if you have the luxury," said Chris. "This exercise falls into the category of what I call 'blue collar conditioning,' and it is a great way to build strength, let out your aggression and burn calories. To me, this kind of conditioning beats the treadmill any day."
Don't have a tire to hit with a sledgehammer? Do a woodchopper, which uses the same motion, but with a medicine ball (and no tire). If you're at a CrossFit gym or have access to a tire and hammer, Chris says "make sure you use your core when swinging the sledgehammer, as you would when swinging a baseball bat.