Sit and Stand. It's the single most important exercise you can do, says Stephanie Richardson, M.S., exercise physiologist at Canyon Ranch in Tucson. Why this exercise, and not the push-up, the pull-up, running, or walking? Well, a strong predictor for independence and good health as we age is quadriceps strength. And this simple, do-anywhere exercise strengthens the leg's largest muscle and increases your chances of living well and long.

Here's what you've got to do to get yourself some strong legs, says Richardson:

• Stand in front of a chair, toes pointing straight ahead, and slowly sit down, watching to be sure that your knees track directly over your heels. (Do not let the knees come forward of the toes -- do let your buttocks stick out behind you).
  
• Let your arms come up for balance.
  
• Touch the front of the seat with your buttocks, then slowly stand up again, keeping knees tracking forward the whole time.
  
• Work up to three sets of 10, three days or more a week.
  
• As this becomes easy, add hand weights or pin an exercise tube under your feet and pull up on the handles as you stand.
  
  

That's it, says the Canyon Ranch guru. Think you can master it? Think it really is the most important exercise?