Interval training: more benefit, less fatigue.

New federal guidelines announced in January 2005 advise adults to exercise moderately to vigorously for about an hour most days just to prevent gaining weight as they age. Those who’ve lost weight need even more activity, up to 90 minutes of moderate exercise, to keep the pounds off. Only the relatively few who have no trouble controlling their weight can meet their exercise quota in as little as a half-hour, the guidelines indicate. (For people seeking to lose weight, the report merely recommended increased physical activity and reduced caloric intake.)