Exercise is good for mental health

I'm all about walks in the morning, and going for a splash in the summer heat...

but, in the process of looking for (free) open courseware from Harvard (that I thought I found earlier), I ran into this course description (Exercise and the Brain):

This course is designed so that participants will be able to:
-instruct their patients on the brain changes resulting from routines of physical aerobic exercise that will help manage mood;
-instruct parents and children as to the many ways aerobic exercise makes the learner better prepared to learn by changing the attention, motivational, and impulsive control level as well as the many alterations that make the neurons ready to learn at the cellular level;
-prescribe aerobic exercise regimens for patients to be maximizing their emotional health and cognitive function as they age.

SO
if you want to lie in bed all day, do so at your own risk. Up! Up!
Endorphins, I think, is a big part of this. One counselor told me to take up ballroom dancing.