Weekend exercise warriors are learning what every professional athlete already knows -- stretching improves flexibility and can enhance performance.

Stretching -- not to be confused with a warm-up, where the body's temperature increases -- makes tendons and ligaments used in exercise more fluid and releases tension that builds up from sitting stationary all day.

It is the area surrounding the muscles and not the muscle itself that is usually involved in stretching, said Dr. Peter Jokl, professor of orthopedics and rehabilitation at Yale University School of Medicine.

Around the muscles are tendons, which connect muscles to bones; ligaments, which hold joints together; and connective tissue, which keeps muscles properly aligned in the body.

"With stretching," said Jokl, "you are trying to elongate the tendon and connective tissue between the muscle fibers. The connective tissue is a lot like Tupperware, and if you warm it up, it becomes more pliable."

As people age, tendons and joints become tighter and this is more noticeable after age 28, said Dr. Richard Grossman, director of sports medicine at Georgetown University Hospital.

Collagen fibers in the ligaments and tendons lose a certain amount of water and elasticity with age, said Grossman, who is also a team physician for the Washington Capitals and the Washington Bullets. Stretching becomes more essential in reducing the tightness the occurs naturally with age.

Current thinking among exercise physiologists suggests that stretching can reduce the injury rate among athletes or people who regularly exercise. However, there have not been enough large-scale scientific studies done to support this.

"We assume people will have fewer injuries if they stretch first," said Dr. Ronald M. Lawrence, assistant clinical professor at UCLA School of Medicine and secretary of the American Academy of Sports Physicians. "But there has not been a good epidemiological study done in this area, as there should be."The proper time and best way to stretch are still debated among sports medicine experts. But there is general agreement that warming up first before stretching can limit the chances of tearing fibers within the tissue.

"Your tissue is like silly putty, and you can stretch it more easily if you warm it up," said Letha Hunter-Griffin, a clinical instructor at Emory University in Atlanta and a staff member of Atlanta's Peachtree Orthopedic Clinic.

People who don't warm up or stretch and just go out and play tennis or football tend to have a greater number of soft tissue injuries such as tendinitis -- inflammation of the tendons -- or muscle strain -- partial tearing of the muscle, said Hunter.

There is also agreement that the best stretching method to use is one that involves a slow, static stretch. Bouncing and stretching until it hurts -- part of the "no pain, no gain" theory of exercise -- is now considered a hazardous approach.

Bob Anderson, author of the book "Stretching" (Random House, $9.95), breaks down the proper way to stretch into two parts -- the easy stretch and the developmental stretch.

"When you begin a stretch," he writes, "spend 10-30 seconds in the easy stretch . . . Go to the point where you feel a mild tension, and relax as you hold the stretch. The feeling of tension should subside as you hold the position. If it does not, ease off slightly and find a degree of tension that is comfortable."

The next step is to gradually move into the developmental stretch. "Move a fraction of an inch farther, until you again feel a mild tension and hold for 10-30 seconds," Anderson writes.

"Stretching," first published in 1975, shows people basic stretches to do for all the major muscle groups and provides stretching routines for specific sports covering everything from tennis and golf to skiing and hiking and the martial arts.

Anderson thinks people spend too much time comparing themselves to others and try to stretch harder to gain the same level of limberness that other people have.

"Some people don't have the ability to become as limber as others, and they should concentrate on their own body instead," he said.

Anderson's own stretching routine starts at his feet. "I spend a minute or two massaging my feet. Then I work on my calves, my knees and quadriceps with light stretching to reduce the feeling of tightness. I stretch the front of my hips and lower back. Then I do one or two light hamstring stretches. Then I work on my neck and shoulders.

"People should figure out what works best for them," he said. "The emphasis for me is on being relaxed and not holding my breath."

One problem with stretching is people may not realize they have injured themselves until the next day. If a person strains a hamstring or an Achilles' muscle-tendon group, more time has to be spent stretching that area out before exercising again, Emory University's Hunter said.

Because gradual stretching can make sore tendons and ligaments feel better, some sports medicine experts think stretching out before and after exercise is the best approach. That means a basic fitness routine could involve: warming up, stretching, exercising, cooling down and re-stretching.

And all that takes time.

But the benefits of stretching can outweigh the time investment as long as the stretch is done properly.

"Obtain a book showing proper stretching techniques," said Hunter. "If there is any question that the stretch is causing pain, ask someone who is involved in an exercise program."

If people feel they cannot mimic the stretches based on pictures in a book, "it is probably a good investment in time and money to take a stretching class with a certified exercise physiologist," Hunter said.

Resources

The book "Stretching," by Bob Anderson, is available for $10.45. Anderson also produces a one-hour video on stretching for $29.95. Send check to Stretching, Inc., P.O. Box 767, Palmer Lake, Colo. 80133. (303) 481-3928.