A LOT OF YOU have your own exercise routines that you've been doing for years, but are the exercises safe? Are they efficient? Are you maximizing your workout? Here are some dos and don'ts:

QUADRICEPS STRETCH

A lot of people stretch these thigh muscles by kneeling and leaning back onto their legs. Don't sit or stretch in this position on your lower legs (or let your children either), since it places dangerous stress on your knees, especially the cartilages inside the knee (the menisci) and the medial collateral ligament on the inner border of the knee.

Do stretch from a standing position: With one leg bent, grasp the foot and pull gently to give your thigh a good stretch. Hold for 15 seconds, then switch legs. (You may need to hold on to a chair or wall with your free hand for better balance).

DEEP KNEE BENDS

Don't bend your knees all the way to a 90

angle; the strain on your knees can damage cartilage and cause chronic knee problems.

Do bend your knees only about halfway (to a 45

angle approximately) to strengthen your thigh muscles. Hold for 15 seconds.

LEG LIFTS

Don't arch your back or throw your leg up high; this strains the back and fails to work the gluteal muscles.

Do rest on your elbows and keep your head in line with your back. Slowly lift the leg so that your hips are level. This prevents the back from arching as it tones the derriere and back of the thighs. Perform slowly 15 times. Switch legs and repeat.

TIPS

Do take time to warm up before you begin to exercise strenuously. Get your blood circulating and give your muscles a thorough stretch. Begin exercising slowly, then work up to a pace your body can handle.

Don't exercise vigorously outdoors if the temperature or wind-chill factor is below freezing, or above 90

with humidity of 80 percent or more.

Don't jog or run with leg weights. That adds stress to the lower leg, which can result in heel spurs, stress fractures, shinsplints, and bruised and aching feet.

Don't try to keep up with friends, classmates or teachers. Their fitness levels and abilities will differ from yours. Beginners should guard against being overambitious, advanced exercisers against being overzealous. Always be true to your own body!

Don't run on paths near congested automobile routes (such as the one along Rock Creek Parkway) during rush hour; inhaling exhaust fumes can be as bad for your lungs as cigarette smoking.

Don't run on asphalt or cement if an alternative is available. Be sure your shoes are in top condition and run slower and take lower steps than usual, to reduce shock.

Don't skimp on exercise clothing. Wear good quality shoes that fit well and are designed for the type of exercise you are doing -- aerobic, running and tennis shoes are each designed for specific kinds of movement.

Do take time to do cool-down exercises after a workout, to help ward off muscle cramps and lightheadedness.

Do keep it up!