One of my goals for these posts is to use individual studies to point out the broader trends they suggest.  This week I want to focus on our increasing understanding of the value of exercise after illness or injury.  A generation ago a heart attack meant weeks of bed rest in the hospital followed by strict instructions from the doctor to take it easy.  The weakened heart couldn’t take much exertion, we thought.  Now after a heart attack patients are told to start exercising as soon as they’re ou...