Intensity Trumps Duration

Researchers in the area of muscle biology and aging have been finding growing evidence that prolonged aerobics training increase the risk of oxidative damage in the muscle. This type of training causes overwhelming accumulation of free radicals in your muscle, which eventually increase the risk of oxidative damage in your tissues (myofibrils and mitochondria). And this risk of oxidative damage becomes increasingly higher as you get older.

On the other hand, intense exercise protocols which are inherently short, have shown to lower this risk. The short intense exercise protocol gives the muscle the time it needs to recuperate and counteract oxidative stress without depleting its antioxidant pool. And again, short intense exercise yield the right impact needed to trigger your mTOR and increase muscle mass.

But there is more to it.

The mechano-overload impact of intense exercise works directly on your fast muscle fibers, the type IIB and the type IIA. It's the fast muscle fibers that enable you to be strong and fast, and they have the largest capacity to generate force and gain size.

You need them when you climb stairs, carry heavy grocery bags, chop wood or move furniture. And if you lose that physical capacity, you lose your ability to live independently.

http://fitness.mercola.com/sites/fitness/archive/2011/01/05/best-way-to-prevent-inevitable-muscle-wasting-as-you-age.aspx

In other words, as my friend Crusader tried to tell me in college, jogging isn't good for you.  Sprints are good for you, lifting heavy weights (relatively heavy, and a little bit more each week) is good for you, and high intensity mixed modal intervals (CrossFit) is good for you.  Intensity trumps duration!

There's a lot more in this piece, and I urge you to ignore most of it, particularly the math drill on leucine quantity - you can reach your goals without performing unnatural acts with whey protein, leucine loading, and other massive doses of obscure supplements.  Eat meat and vegetables, nuts and seeds, some fruit, little starch, and no sugar/wheat, supplement vitamin D to make up for our lost capacity to make it for ourselves through sun exposure, and take enough fish oil to make up for the extra omega 6 fatty acids our industrial food chain gives us. That's the critical 80% you need to be well, feel good, and perform at a high level.