From this Science Now Daily News article A Connection Between Sleep and Alzheimer's?:
The positive adaptation as a result of aerobic activity is primarily a bio-chemical change - the body up-regulates its ability to burn sugar for an extended time. The recovery period is short - hence running can be done with greater frequency. The positive adaptation resulting from strength training involves a structural change - the rebuilding of muscle. For most that involves several days to be fully recovered. Think how long it takes an injury to totally heal. Some go back to the gym before being fully recovered and as a result make minimal progress. Some repeat this mistake for years. I was one of them.
Many years ago when I first started strength training I followed the conventional wisdom that stated that you had to give yourself a day off between strength training sessions to let your body recover and become stronger.
From this Medscape article Fruits, Vegetables, and Coronary Heart Disease these bullets:
From this NYT article VITAL SIGNS RISKS; Midlife Cholesterol Tied to Alzheimer's:
From this NYT article Splits Form Over How to Address Bone Loss: