NEW YORK (CNN) — We often hear about the importance of stretching, especially after exercise, to improve flexibility. Indeed, studies have found that regular stretching can increase flexibility in as little as four weeks. But getting results requires commitment: You need to stretch at least three days a week, ideally every day. Activities such as yoga and Pilates can improve flexibility, as well.

How flexible you are and how flexible you can become are also influenced by factors that you can't control, such as genetics and gender. As anyone who has ever observed a co-ed yoga class can attest, women tend to be more flexible than men. Injuries and certain conditions like arthritis can also limit flexibility.

Age plays a role, as well. Starting around age 30 or 40, flexibility continuously decreases, with men losing flexibility more quickly than women. But this decline doesn't occur uniformly throughout the body.

Research shows that the shoulders and trunk tend to lose flexibility more quickly than the elbows and knees, for example. At any age, you may be relatively flexible in one part of your body and have limited range of motion in another. Flexibility can also vary from one side to another.

As for how much flexibility is optimal, there's no definitive answer. We know that having poor range of motion can hamper athletic performance, increase the risk of injuries and make tasks of daily living more difficult. It's also true that a high level of flexibility can be beneficial if you do activities such as gymnastics, swimming or ballet. But this doesn't mean we should all strive to become human pretzels.

Just as extreme inflexibility can lead to problems, so can extreme flexibility. People who are double-jointed — or have "joint hypermobility," as the condition is technically known — are more likely to experience pain and sports-related injuries. Interestingly, they're also at higher risk of anxiety disorders. (Why the two conditions are related is unknown.)

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Between the two extremes is a wide range of satisfactory flexibility levels. Being on the upper end of the range may impress your friends in yoga classes or games of Twister, but it won't necessarily confer any additional health benefits.

Instead of worrying about how your flexibility stacks up against that of others, you should focus on what's right — and realistic — for yourself. Assess what your needs are and how stretching might address them. For example, maybe a certain part of your body is especially inflexible and holding you back in your workouts. Or perhaps you want to improve your flexibility to help your tennis or golf game, or to get on the floor and play with your kids or grandkids.

Whatever the case, here are a few relatively simple tests you can use to assess your flexibility. Do them after a warmup or workout.

Sit and reach

Developed in the 1950s, this classic test of flexibility in the hamstrings and lower back has several variations. Here's a DIY version from the YMCA that requires only a yardstick and masking tape.

• Put the yardstick on the ground with a strip of tape across the 15-inch mark.
• With your shoes off, sit on the floor with the yardstick between your legs and the 0-inch end closest to you.
• Keep your legs straight and your feet about 12 inches apart. Sitting up straight, position your heels at the 14-inch mark.
• Place one hand directly on top of the other and slowly reach forward as far as you can without bouncing. Drop your head if it helps, and be sure to exhale as you stretch.
• Note where the ends of your fingers reach on the yardstick. Repeat two more times and record the farthest distance.

Zipper

This test of shoulder flexibility measures how closely you can bring your hands together behind your back. You need a tape measure or ruler and an assistant.

• Stand and raise your right arm above your head. Bending your right elbow, reach behind your head with your palm touching your body. Reach as far down the middle of your back as you can, with your fingers pointed down.
• Place your left arm behind your back with your palm facing out and your fingers upward. Reach up as far as possible and try to touch your other hand.
• Have someone measure the distance between the ends of your middle fingers. If they don't meet, record the length of the gap as a negative number. If they touch, score that as a zero. If they overlap, record the length of the overlap as a positive number.
• Do the test two more times and record your best reading. Then switch arms, putting your left hand behind your head, and repeat.

Sitting-rising

This test, developed by a Brazilian doctor, has received attention as a tool to predict mortality risk in middle-aged and older people. But research suggests that it can also be an indicator of flexibility (as well as strength and balance) in people of all ages. No equipment is required, but you need sufficient space and a surface that's not slippery.

• Standing barefoot, try to sit on the floor with as little support as possible from your hands, legs, arms or other body parts. Crossing your legs is fine.
• From the seated position, try to stand up, again with as little support as possible.
• Give yourself a score of 5 if you sat with no support at all and 5 if you got up without support. For each support required, such as a hand, forearm, knee, side of a leg or hand on a knee, subtract 1 point. Subtract a half-point if you were wobbly sitting or standing.
• Do the test twice and combine your best scores sitting and rising.

There's no need to get perfect scores on these tests — though if you do, that's great. Instead, use the results to track improvements in flexibility over time. That way, you can tell whether all those shoulder stretches or Cobra poses are paying off.

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