?21 Jump Street? premiered on this day in 1987, delivering a blend of high-energy police work with hard-hitting public-service announcements. For this reason, it's a great backdrop for today's tip about exercise in moderation. If you haven't worked out or done jumping jacks in a long time, go easy at first. Too much too soon causes injuries. Start slowly and build endurance. Many are hurt using weight machines improperly. Learn first from a qualified instructor, and remember ?no pain, no gain? is a dangerous myth. For the average Joe or Jane pain is nature's warning to back off. Running injuries are frequent in those who do more than 30 miles a week. Sports-medicine doctors say 20 to 25 miles is enough to stay in top condition. Any hard exercise in hot, humid weather can cause heatstroke. Always drink lots of water before, during and after running or other strenuous exercise. Exercise can be addictive. Beware of overdoing it, and don't let it interfere with your work or social life. And that's the On The House tip for today.