I am borrowing this from an email I got from Dr. Mark Hyman---he's got a lot of great information if you're interested in his Ultrametabolism perspective http://www.ultrawellness.com/blog/
"What did our caveman ancestors know about exercise that we didn't?
After all, they didn't spend hours in the gym doing painfully long aerobic sessions.
But they did have incredible strength, speed and stamina.
If they saw a threatening animal like a saber-toothed tiger or even a hungry dinosaur coming at them...you guessed it, it was time to run, and fast.
So what did our cavemen ancestors know that we don't?
It's something I've talked about repeatedly in my books and blogs and it's the same principle that underlies my dietary recommendations.
What they did was do what their genes had evolved to do -- exert tremendous amounts of energy in a short period of time.
They didn't run for hours on end, starve themselves with ridiculous diets or lift boulders over their heads to build bigger muscles.
Cavemen followed natural cycles of work and rest, or what I call periods of exertion and recovery.
This helped them to build their reserve capacity -- their ability to exert tremendous amounts of energy in a short period of time.
Reserve capacity means your heart has the ability to pump more blood, faster in times of stress.
Reserve capacity for your lungs allows them to deal with high exertion like lifting, carrying, running or going up stairs.
And not only did this help caveman build incredibly strong hearts and lungs, but it also made them lean, fat burning machines, which I'll explain why in a second.
The big takeaway here is that if eating like our ancestors did leads to health and vitality, then it makes sense that we should exercise like our ancestors as well...just as our bodies were designed to do.
And thankfully, by exercising the way our ancestors did, we can not only spend less time exercising -- as little as 12 - 20 minutes per day -- but we can strengthen our hearts and lungs and reduce the risk of heart attacks or developing breathing problems.
You've actually heard of this type of exercise before -- it's called interval training and can have powerful effects in a very short period of time.
A few years ago, Harvard researchers published the Harvard Health Professionals Study.
After studying over 7,000 people they found that the key to preventing heart disease is intensity - NOT long-duration exercise.
What's more interesting is that in another study, researchers found that by doing the right type of interval training, people continued to burn fat for up to 24 hours after the interval training session."