STRENGTH Why it matters: Pumping iron (or just using your own body weight for resistance) increases bone density, boosts metabolism and makes you more self-sufficient for daily tasks. Exercise: Push-up From a plank position with hands slightly wider than your shoulders, lower your knees to the floor. Lift your bellybutton toward your spine and draw your lower ribs together. Keeping your knees, hips, shoulders and head in one plane, bend your elbows out to the side and reach your chest (not your chin) toward the floor. Aim to bend your elbows 90 degrees before pressing back up to the starting position. Do as many as you can while maintaining proper alignment and lowering with control. How to tell you’re improving: The number you can do increases. After you can do 20 on your knees with proper form, straighten your legs and do them off your toes.