Q. I'm in my 50s and in fairly good shape. I work on the ninth floor of my office building. If I walk up the stairs (instead of using the elevator), will it help my heart and cardiovascular system? Are my muscles getting any benefits? Will I lose any fat? Is this a waste of time or should I just take the elevator?

C.H.

Alexandria.

A. My first bit of advice is take the elevator until you've visited your doctor for a complete physical. Exercise is an emergency for the body. If your fitness level is high enough, you'll meet the body's needs successfully. If not, your friends may be reading about you in tomorrow's paper. You've probably seen these kinds of headlines before: "Executive Drops Dead Running Through Airport"; "Man Dies of Stroke While Shoveling Sidewalk."

Don't become one of those statistics. If you're over 35 and/or overweight, see a doctor for a complete physical before engaging in any new exercise.

Let's assume you've visited the doctor and he's okayed your climb. Then I'd encourage you to use the stairs instead of the elevator. Your office job renders you fairly inactive, so any exercise is a bonus.

Just how beneficial will your ascent to the ninth floor be? It's better than nothing but don't expect it to help you vie for an Olympic berth. The benefits for your heart and lungs (cardiorespiratory system) will be almost non- existent.

Why? To improve heart and lung efficiency, exercise must be sustained for a minimum of 12 minutes and preferably 20 to 45 minutes. Your heart rate must be at 70 to 85 percent of its maximum to elicit an aerobic improvement.

If you are 50 years old, your maximum heart rate is 170 (220 minus your age). Seventy to eighty-five per cent of 170 is 119 to 144. To improve your aerobic efficiency, you would have to keep your heart rate somewhere between 119 and 144 for a minimum of 12 minutes. So it's probably obvious to you by now -- climbing nine flights of stairs will not improve your cardiorespiratory fitness.

How much fat will you burn climbing nine flights of stairs? If you weigh 150 pounds, for example, you'll have to climb a ten-foot flight of stairs approximately a thousand times to lose one pound of fat. If you climb those nine flights once a day, you'll use up enough calories to lose approximately one pound of fat every four months. It's not a very effective way of burning calories by itself, but combine it with all of your other daily activities and it helps.

How beneficial is it to the muscles involved? Well, again, it's better than nothing. There are some benefits but not enough to make a difference in muscle tone or strength.

However, your willingness to climb nine flights of stairs indicates you won't be one of the people I see driving around the parking lot for 20 minutes waiting for a parking space right next to the store you're shopping in. So I'm betting that walking the stairs isn't your only activity and that the sum total of your activities means you're doing quite a bit to stay fit.

If it doesn't adversely affect your health, climb the stairs instead of riding the elevator. Just recognize that it's not a substitute for a properly organized and administered aerobic and musclar fitness program. And remember, take one step at a time.