What is it that makes my muscles so sore?

You've had a health checkup and found that you have exceeded your fat content. So you drag yourself to an exercise class. Feels great to sweat doesn't it? That is until the next day.

Your body has more than 425 voluntary muscles, and every one of them will complain after one hour of fitness. The only part of you that won't be sore is your lips and your earlobes!

It doesn't seem fair that something so good for you can be so painful. Well, you aren't alone; the air around town is permeated by the groans of new and "renewed" fitness students. Even the fitness student who participated in a different sport for the winter will find a few sore spots when returning to summer exercise.

Why are you sore? There are so many theories regarding this subject. Muscles move every part of your body. You need them to talk, eat and even to breathe. And they all produce a movement by lengthening and shortening. When a muscle shortens, it strengthens. At the same time the opposing muscle lengthens. This back and forth action puts stress on muscle tissue, and can cause small pulls or tears. Not noticeable during exercise, they can be very noticeable the following day, especially with the large muscle groups such as quadriceps, hamstrings and calf muscles.

How many of you women wear high heels to work? The calf muscles become shorter and they lose some of their elasticity when the heel is continuously held off the floor. When you begin jogging or working out in an aerobics class with low-heeled shoes, the toe-to-heel movements will extend that calf muscle so that your foot is flat on the floor. This will work the calf, hamstring and quadriceps muscles to the point where you can't climb stairs the next day.

Muscle spasms are another painful result from an exercise experience. They are caused by hydroxyproline being released into damaged muscle tissues, and the muscle spasm you suffer restricts the blood flow in the muscle causing more pain.

In any case, the eccentric movement segment of an exercise seems to be the initial cause of muscle soreness. It's the muscle contraction that lengthens against resistance. Stretching the muscles gently before you workout and again following exercise, will tend to prevent, and overcome soreness.

Sore muscles and stiffness that plague new and renewed exercise students can be helped by doing easy smooth swing movements and an easy light jog to get the blood circulating before you begin your workout.

• Jerry Vance is the owner of Sweat Shop/Wet Sweat. She offers classes through the Carson City Recreation and Aquatics Center and is a fitness instructor for the Carson City Senior Citizens Center.