And since they knew that the next hungry T-Rex was coming by in less than half an hour, they had to carry that stuff back to the cave quickly. That is intense work, the kind that builds strength, uses a lot of different muscle groups at the same time, and burns a ton of fat and calories. Cavemen certainly weren t embarrassed to walk around without shirts on. Are you? Hmmm. Intense work. Builds strength, power, and muscle. Uses Multiple Muscle Groups. Burns a Lot of Fat and Calories. Takes Less Than 30 Minutes. Sounds pretty interesting, don t you think? Well then, it's t...