"These same positive benefits apply to children," psychologist Jack Raglin said in a statement. "At the same time, it's becoming more and more challenging to find time for kids to have physical activity. Kids are overly scheduled -- parents have to work at finding avenues for activity."

Raglin, who has conducted research examining overtraining syndrome, meditation and other issues involving mood and exercise, said:

-- People are more likely to experience the mood-boosting benefits after aerobic activities such as jogging, lap swimming or cycling, compared to activities such as strength training.

-- The benefits can be experienced after just 20 minutes of light or moderate activity, such as a slow jog.

-- People who are clinically depressed experience the most mood-boosting benefits, but people who generally already are relaxed, with low levels of depression or anxiety, can still experience the feelings of calmness, lowered levels of anxiety and less fatigue.

-- Intense exercise routines can cause depression in otherwise healthy individuals.