UPDATE: With spring coming, the desire to begin an exercise program increases in all of us. To help you begin that program successfully, I will list and discuss some often misunderstood fitness "myths," which were in a recent newsletter from the President's Council on Physical Fitness & Sports (January/February 1991).

Myth No. 1: No pain, no gain. Many of us are still working out to the point of real discomfort, believing that if some exercise is good, more is better. This approach to exercise can cause injury and discouragement. A well-balanced, moderate workout should leave you feeling invigorated, not aching. You should breathe harder and sweat, but you should not work so hard that your body hurts or that you are discouraged about trying it again. Start out with 10 to 15 minutes of exercise a day and increase only about 10 percent a week.Myth No. 2: Exercise turns fat into muscle. Those extra inches of fat on your waist or thighs cannot be converted to muscle. Fat is fat, and muscle is muscle, and they are two different substances. When you do aerobic work and eat properly, you can lose fat; if you lift weights or do calisthenics, you can build muscle. However, one does not become the other.

Myth No. 3: Playing sports keeps me in shape. It depends. If you play an occasional (once a week) game of golf, you will not be getting enough of a workout to improve your strength, flexibility and endurance. Of course, if you walk the course briskly you will burn extra calories, but the stop and start nature of the game prevents it from being a true aerobic workout.

Recreational sports are important for relaxation, socialization and as a supplement to a fitness program, but cannot replace completely a more formal approach to fitness. Depending on your goals, you may want to add some regular workouts to your week. You might even do better in your sport.

Myth No. 4: The best time to exercise is before dinner. Although exercise may depress appetite slightly, the best time to exercise is the time that fits your schedule best. Early morning risers often find morning the best time for exercise; some office workers may use the noon hour. The important point is to find a time that fits your schedule and avoid exercising immediately after a meal.

Myth No. 5: It's not good to drink water during a workout. Losing too much fluid can be dangerous, and exercise can trigger fluid loss, especially on hot days. Drinking water or sports drinks during short exercise bouts is no big deal, but long-term exercisers should drink fluids on a regular basis during the event.

Myth No. 6: "I'm too old to exercise." It's never too late to exercise, and the benefits are just as important for the old as for the young. For seniors, improved strength, flexibility and endurance mean greater independence, better health and a new outlook on life.THIS WEEK'S HEALTHFUL LIFESTYLE GOALS

- Exercise. Keep exercising from 30 to 40 minutes a day. Your speed will increase as you get more fit, but the feeling of stress should still be the same. Keep doing 25 abdominal curls and 15 squats. Increase to 15 modified pushups.

- Diet. Switch to fortified skim milk.