The health benefits of stretching have been massively oversold

Part of the great fun of watching the Olympics is witnessing athletes smash our expectations of what the human body is capable of.

With the summer games in Rio, we can look forward to admiring gymnasts bend and contort in ways that seem to defy the limits of our physiology, like US gymnast Gabby Douglas here:

Such extreme feats of flexibility may prompt us to question whether we should be working a little harder to touch our toes or do the splits.

If you did the President’s Challenge Sit and Reach test in gym class, you probably learned that flexibility is something to strive for. Or if you ever played a sport, you were likely taught that you should always stretch to prevent injuries and reduce soreness.

But it turns out many of the benefits of flexibility and stretching have been overstated. I asked five researchers, physiologists, and trainers who work with elite athletes (including Olympians) to tell me what they know about flexibility. Here’s what I learned.

What is flexibility?

Flexibility refers to the range of motion in your joints. For some joints, that range will be determined by resistance in surrounding structures, like the ligaments around the elbow. For others, the resistance comes from the muscles — like the hamstring, which determines how far your hip joint moves and whether you can touch your toes.

More flexibility isn’t always a good thing

In some sports, flexibility is absolutely critical. Gymnasts, for example, have to do splits and other extreme skills to compete at elite levels. Ditto for divers and synchronized swimmers, who bend and contort in the air and the water. On the field, you'll also see pole vaulters, high jumpers, and triple jumpers arching their backs to nearly unfathomable degrees.

But "one of the biggest misconceptions is that more flexibility is always better," said sport physiologist Trent Stellingwerff of the Canadian Sport Institute.

The desired degree of flexibility depends on the range of motion in the sport you're doing: Wrestling, for example, involves many more kinds of movement compared with cycling and distance running.

"In distance runners, the worse an athlete’s flexibility, the better their running economy, which is linked to marathon performance," said Stellingwerff. So elite runners actively avoid becoming hyper-flexible. "They need to be flexible and mobile enough to have a great range of motion," he added. "But the stiffer they are, the faster they will run."

Same goes for cycling, said Asker Jeukendrup, an exercise physiologist and sports nutritionist who has worked with Olympic champions and Tour de France cyclists. "[With cyclists], stretching is only a small part of a daily routine and the athletes are relatively inflexible," he said.

Flexibility for non-athletes

For those of us non-athletes, having some flexibility is important for healthy living, said Jay Hertel, a kinesiologist and professor of sports medicine at the University of Virginia. "You need to be able to go through a functional range of motion from the standpoint of being able to do activities of daily living." Flexibility helps with reaching or bending to pick something up without hurting yourself, for example.

But, again, too much of it isn’t a good thing. "You can have too much range of motion; being overly flexible can be potentially risky for injury as well," he said.

For example, studies in military populations show that if you take different flexibility measures, the soldiers who are neither the least nor the most flexible fare the best when it comes to injury risk.

Some people are just more flexible than others. Blame genetics.

Growing up, I had a friend who could strike almost any pose with very little effort. She was bendy when I could hardly do the splits.

Part this difference has to do with levels of physical activity over your lifetime. "If you don’t move through a joint’s full range of motion, you can definitely develop a limited range of motion," said Hertel.

Then there are genetic components that influence the type of collagen — the protein that makes up most of the musculoskeletal soft tissues in the body. "Some people have a higher proportion of the more flexible types of collagen than others," Hertel added.

Besides these differences in genetics and exercise history, "we are also anatomically surprisingly diverse when it comes to our bones, joints, tendons, ligaments, and muscles," said Jeppe Bo Lauersen, a researcher in Copenhagen. This diversity expresses itself in varying degrees of tissue and joint flexibility, Lauersen explained, "even before we begin treating them with stretching or training."

Stretching has been oversold — especially as it relates to workouts

If you hang around gyms and yoga studios, you might be told that stretching will deliver health benefits ranging from reduced sugar cravings and lifted moods to better running performance.

But such claims haven't been proven with science.

"To my knowledge, there’s no well-designed experimental study that has ever proven any hypotheses about disease or improving physiological outcomes by being flexible," said Lauersen.

There is some evidence that stretching and flexibility-focused exercises like yoga can help people get in touch with their body and improve symptoms related to stress, anxiety, and depression. "This is probably more a result of the process of stretching than the resulting flexibility itself," Lauersen said.

Relatedly, stretching isn’t as helpful as you might think for preventing injury and muscle pain when you play sports. For a recent systematic review on the evidence on different exercises to prevent sports injury, which looked at 25 trials with more than 26,000 participants, Lauersen found that stretching was one of the exercises that actually didn’t have a significant effect. (Strength training, by contrast, had the most significant effect on reducing sports injuries.)

That conclusion has been echoed in other systematic reviews on stretching before and after exercise to prevent injury and muscle soreness. A more recent randomized trial on stretching for muscle soreness and injury again found no effect on injury, and a small benefit for muscle soreness.

"There are some beneficial effects of stretching, but they are very small and have been oversold," said , one of the authors of these studies and a leading stretching expert. "For the research that’s been done up to now, it looks like there’s little or not effect on injury, and a very small beneficial effect of stretching on soreness — but that’s probably so small most people wouldn’t be able to perceive it."

And while some claim that different kinds of stretching — dynamic versus static, for example — produce different outcomes, Herbert warned, "They are almost invariably expressing an opinion not based one evidence, since there’s really been no systematic investigation of the differences in outcomes with different types of stretching."

But if you want to become more flexible, here’s one thing that helps

If you like stretching, Herbert says, it may indeed help reduce soreness to some small degree. And if it feels good, by all means, go ahead.

But you’re stretching to boost your athletic ability, you may want to consider whether your sport of choice really requires that extra bendiness.

Whatever the aim, the biggest key to becoming more flexible is sustained effort.

"Doing exercises once or twice a week isn’t going to do it," Hertel said. "It needs to be almost a daily occurrence to get the best benefits out of the flexibility program."

He’s also noticed that using foam rollers before stretching can help move things along a little more quickly. The rollers loosen up the connective tissue the surrounds the muscle called the fascia (you can read about the fascia in our explainer). "It’s not necessarily that all inflexibility comes from the muscle itself being tight," he said. "Part of it can be the fascia that can be tight."

But you’re not missing out on much if you confine your appreciation of flexibility to watching gymnastics on TV. "If you don’t like stretching," said Herbert, "don’t bother."