A May 3, 2007 New York Times article, A Healthy Mix of Rest and Motion, suggests that for at least one workout a week it pays to alternate short bursts of high-intensity exercise with easy-does-it recovery. This type of high intensity interval training comes in many forms.
From this article High-intensity exercise better at improving metabolic syndrome risk factors;
From the article The Best Exercise for Diabetics:
Something my brother sent me that I thought was worth sharing:
From Men's Health magazine article 5 Reasons You're Not Losing Weight:
1. You Eat Fat-Free Foods 
2. You (Still) Don't Eat Breakfast
Q. Is there anything you can do to keep your brain healthy and improve the deficits, like memor
y problems?
We burn calories four ways. One of the ways is the burning of additional calories after the exercise session is over.
It has long been assumed that if you don’t head back to the gym a few days after you last session your positive results will begin to dwindle. Take a couple weeks off from 
running and you will find that that will usually be that case. Take a week or two off from weight training and you might find that you come back stronger.
