The lowdown on stretching: How flexible do you actually need to be?

New Scientist Default Image

Harriet Noble/Studio Pi

“I BEND so I don’t break.” No one knows who first coined this phrase, but search for it online and you will find it accompanying numerous pictures of yogis in various states of contortion. Flexibility, according to common wisdom, is not only impressive to look at, but something we should actively work towards.

Scientifically, however, the question of whether we should stretch to become more flexible has been difficult to answer. Assumptions about the benefits of stretching to prevent sports injuries and greater flexibility being better for our overall physical fitness hadn’t been confirmed by studies. Does it matter if you can’t touch your toes, let alone do the splits? Even in sports science, where most of the research has been conducted, there has been little agreement.

In recent years, though, answers have started to emerge. The surprising outcome is that, while stretching may well be good for us, it is for reasons that have nothing to do with being able to get your leg behind your head.

One thing is for sure: stretching feels good, particularly after a long spell of being still. We aren’t the only species to have worked this out. As anyone with a dog or cat will know, many animals take a deep stretch after lying around. This kind of stretching, called pandiculation, is so common in nature that some have suggested it evolved as a reflex to wake up the muscles after a spell of stillness.

Pandiculation aside, other species don’t seem to spend any time maintaining and extending their range of motion. Which raises the question, is there any reason why we should?

Our flexibility is controlled by the tissues of our musculoskeletal system, which determine the maximum range that our joints can move without causing injury. For a long time, flexibility has been considered a key component of physical fitness (along with cardiovascular endurance, muscle endurance, muscle strength and body composition – the percentage of body weight which is muscle, fat and bone) by groups such as the American College of Sports Medicine. Its latest guidelines, for example, recommend stretching all the major muscles groups at least two or three times a week, holding the stretch for anywhere from 10 seconds to 1 minute.

But even for exercise-phobes, there are good reasons to stretch: our species is unique in having invented a way of resting that works against the needs of our bodies. Anthropological evidence suggests that from at least 2 million years ago, and until the invention of chairs, our ancestors rested by squatting on their haunches, a position that is still common among young children, modern hunter-gatherers and in cultures across Asia. For those who are used to it, squatting is a comfortable resting position, and has the added bonus that it keeps the hips, calves and ankles mobile through the range of motion needed to walk, run and otherwise move around in the world.

Resting in chairs, however, does the opposite, causing us to stiffen up. A study last year by researchers at the University of Salford, UK, suggested that this has a real impact on range of motion. People who regularly sat for less than 4 hours a day and were generally active had 6 degrees more range of motion in their hip joints than less active people who sat for more than 7 hours.

There is also evidence that sedentary lifestyles in general are having a knock-on effect on overall flexibility. A 2012 analysis by the US Institute of Medicine in Washington DC of data from the now-defunct Presidential Physical Fitness Test, which, between 1966 and 2012, included a sit-and-reach flexibility test for all US schoolchildren, found that flexibility in young people had decreased over the decades, particularly among boys.

By early middle age, the most sedentary people are so stiff that they can injure themselves even while sitting at a desk. “We see that starting at age 30 or so, people get problems from non-sporting activities like moving the computer mouse,” says Markus Tilp at the University of Graz in Austria, who studies stretching.

What’s more, it isn’t just the physical act of sitting that leaves us feeling tight. Concentrating on a mental task contributes to tension in the shoulder girdle, arm and neck. This is partly because when we focus our eyes on a screen, we often tense our shoulders to increase our ability to focus visually (and mentally). One study found that the trapezius muscles in the upper back, which help keep the head upright, are particularly sensitive to the difficulty of the task – the more we need to concentrate, the more they tense up.

For people who sit a lot and are under a lot of stress, then, stretching and mobilising stiff parts does relieve tension and lengthen muscles – at least temporarily (see “What happens when you stretch?“). It is also well known that, when done regularly, stretching can lengthen muscles and connective tissue, restoring their length and a full range of motion to underused joints.

“Sedentary lifestyles are having a knock-on effect on flexibility”

Which sounds like case closed for the benefits of stretching, especially for those who feel their bodies are tight, weak and inflexible. But this doesn’t necessarily mean we should devote lots of time to stretching to get more flexible as part of an exercise regime. In fact, according to exercise scientist James Nuzzo, this type of stretching isn’t worth the effort.

Nuzzo says that the hype about stretching dates to 1980 when exercise scientists Charles Corbin and Larry Noble, then at Kansas State University, first made the case for its importance in overall health. They argued that flexibility was important to maintain posture and protect the back, while allowing the body “freedom to move”. Soon afterwards, the sit-and-reach test was incorporated into the first version of US standardised physical fitness tests as a measure of flexibility, and the idea that stretching is the way to improve flexibility became entrenched in the popular consciousness. However, in his 2020 paper “The case for retiring flexibility as a major component of physical fitness“, Nuzzo, then at the University of New South Wales in Australia, argues that, while maintaining a healthy range of motion is important, stretching has a reputation that far outstrips what it can actually do for our physical fitness.

For a start, the degree of flexibility you need very much depends on what you plan to do with your body. Normal human movement only requires the hips to be sufficiently flexible to allow the legs to extend backwards to an angle of 30 degrees from upright. In other words, for everyday activities, you only really need the flexibility to get halfway to the splits, at most, and there is little reason to push your hips any further.

Bending to extremes

What’s more, the kind of extreme flexibility that makes a great social media post can be more trouble than it is worth. As many as 20 per cent of people have hypermobile joints, which extend further than the normal range. This can lead to physical problems, such as joint pain and dislocations, if the joint hasn’t been strengthened throughout its full range. Most cases of joint hypermobility are inherited, caused by an unusually loose form of collagen, but some researchers think that certain types of extreme stretching – dance training, for example – can lead to joint hypermobility and the problems this can cause. This suggests that a training regime with flexibility as its sole aim may not be such a good idea.

New Scientist Default Image

Harriet Noble/Studio Pi

Nuzzo’s main problem with stretching, though, is that for our overall health, it’s largely a waste of time. “There is not strong evidence that flexibility really correlates with a lot that’s hugely important,” he says. Cardiovascular fitness, muscle strength and endurance all correlate with a lower risk of mortality, he argues. Flexibility, not so much.

That isn’t to say that we shouldn’t aim to maintain a healthy range of motion, and to extend that range if necessary, says Nuzzo. People who spend most of the day sitting and then exercise in frantic bursts are at risk of doing themselves an injury if they don’t take the time to maintain a useful range of motion. But he argues that there are better ways to achieve this goal than a dedicated stretching regime.

“We need to get out of our minds this notion that stretching exercise holds a monopoly on the lengthening of tendons and muscles,” he says. “It’s not the only activity where flexibility or range of motion will improve when you do it for several weeks.”

Resistance training – in particular eccentric contractions, where muscles are loaded as they lengthen (for example, the lowering phase of a bicep curl or walking down the stairs) – has the same effect on the muscles as pulling them into a stretch, he says. Doing this, you get strength as well as flexibility, with no need to tag on a series of stretches afterwards. “If people only have a limited amount of time and you want to make them healthier, I would argue that taking up chunks of their workout time with lots of stretching is not a good use of their time.”

“There isn’t strong evidence that flexibility correlates with things that are hugely important for our health”

In fact, keeping the joints oiled doesn’t need to involve anything that you might think of as exercise. Squatting onto your haunches when you need to reach something on the floor will release sitting-related tension without the need to contort your body into an “official” glute stretch. Reaching to grab something from a high shelf or playing frisbee will help free up the shoulders too.

The benefits of choosing strong mobility over flexibility is that you get side benefits in terms of increased strength and endurance, which – unlike flexibility – are proven to bring significant benefits for overall health and longevity.

Tilp also says it is a lack of movement, rather than a lack of stretching per se, that causes us to stiffen up in the long term. “We know that when you get older, you become less flexible.” But “if you move your joints through the whole range of motion, that just keeps the flexibility”, he says. Tilp, too, recommends prioritising strength throughout the whole range of motion of the joint. Active stretches, such as yoga poses that involve holding your body weight in a stretched position, like a downward dog, strengthen and stretch muscles at the same time. “You have not only the flexibility but also strengthening,” he says.

But don’t abandon your flexibility training just yet. Not only can it help prevent sporting injuries (see “Stretch then exercise?“), it has surprising benefits for the cardiovascular system as well.

Over the past decade or so, studies have revealed a link between inflexibility and risk factors for cardiovascular disease. For instance, a 2009 study of Japanese adults led by Kenta Yamamoto at the National Institute of Health and Nutrition in Tokyo found that the stiffest participants (as measured by a sit-and-reach test) aged 40 or over had stiffer arteries, and this effect was independent of the aerobic fitness levels of the participants.

What’s more, a 2018 study of 1354 Japanese men aged 35 to 59 found that the least flexible (as measured by the sit-and-reach test, plus range of movement in the shoulder and arm) showed the highest levels of atherosclerosis, the build-up of plaque in the arteries, which is another risk factor for cardiovascular disease. This implies that it may be possible to improve our cardiovascular health via a regime of stretching, or at least by keeping our joints and muscles oiled. A growing number of studies show that this is indeed the case.

New Scientist Default Image

The Australian women’s softball team stretch out in a pre-Olympics training session

Reuters/Kim Kyung Hoon

In 2008, researchers from the University of Texas at Austin were investigating whether strength training could reduce arterial stiffness. Their control group undertook a mild stretching programme: holding stretches of all the major muscle groups for 20 seconds, three days a week for 13 weeks. The unexpected finding was that strength training had no effect, whereas stretching reduced arterial stiffness by 23 per cent.

Unexpected benefits

Another Japanese study found that middle-aged people who carried out a four-week regime of static stretches of all the major muscle groups had significantly reduced arterial stiffness. The mechanism behind this effect is still a mystery, though there are a number of proposed explanations. One is that improving the elastic properties of our skeletal muscle also improves the elasticity of our blood vessels.

Another is that atherosclerosis is an inflammatory condition, which is somehow alleviated by the physiological effects of stretching. Evidence for this comes from studies of the fascia – the layers of connective tissue that surround muscles and allow them to slide over each other. Long thought to be nothing more than nature’s version of plastic wrap, the fascia are now known to be biologically active and may play an important role in the management of inflammation. Experiments by Helene Langevin and Charles Serhan, then both at Harvard University, show that when samples of rats’ fascia are gently stretched, cells within the tissue rearrange to become flatter and longer, whilst secreting anti-inflammatory molecules.

These studies have revealed that stretching injured tissue speeds up healing and increases levels of chemicals called resolvins that are made by the body to turn off the inflammation response. “That suggested that the stretching helped the body to resolve the inflammation – it helped the natural process,” says Langevin.She also stresses that, while stretching may be beneficial, extreme bendiness is likely to be surplus to requirements. Just stretching until you feel it is probably enough, she says.

New Scientist Default Image

You don’t need to go to the gym to exercise your body’s full range of movement

Getty Images/Westend61

In fitness classes, it is easy to get fixated on the bendy people at the front, but there is no need to go to extremes to get the benefits of flexibility. What is most important for physical well-being is ensuring to exercise our body’s full range of movement, and this doesn’t necessarily require a stretching routine at the gym. And although such regimes can help prevent sports injuries, there are side benefits for our cardiovascular system too.

Putting your leg behind your head? Science says: no need.

What happens when you stretch?

The short answer is that the muscles, tendons and fascia – a kind of connective tissue that surrounds the muscles – all get longer, at least temporarily.

While this had long been suspected, it wasn’t until around 10 years ago that studies by Markus Tilp at the University of Graz in Austria using ultrasound confirmed that stretching temporarily increases the length of the muscle-tendon unit by between 5 and 10 per cent. The effect comes down partly to the lengthening of individual sarcomeres, the basic units of the muscle, and partly down to viscoelastic effects that make the muscle and connective tissue more pliable for an hour or so.

In the medium term – six to eight weeks, say – studies have found that a regular programme of stretching significantly increases range of motion. However, no changes in the muscles or other tissues have been identified on this timescale. This has led Tilp and others to speculate that increased range of motion is explained by an increase in stretch tolerance: essentially, a sign that the nerves don’t sound the pain alarm so easily, because the nervous system has learned that this level of extension is safe.

Less research has been done on what a long-term programme of stretches does to the muscles and other tissues. Observations of ballet dancers suggest that, over long periods, individual muscle fibres do get longer, which may be caused by adding new sarcomeres to the muscle’s length. Tilp’s study on this was postponed during the pandemic, however, so we still don’t know for sure.

Stretch then exercise?

A quick warm up followed by stretches was once the staple of pre-exercise preparation to prevent injuries and prepare the body to move. But studies on the benefits gave conflicting results, leading people to question if stretching makes exercise safer, and even whether it could harm performance.

Then, in 2016, David Behm at Memorial University in Newfoundland, Canada, and his colleagues reviewed the evidence. They concluded that, while much is still unclear, stretching before exercise is more beneficial than it is harmful for both injuries and overall performance.

In terms of preventing acute muscle injuries, the team found that stretching before exercise reduced the risk of injury to muscles by up to 54 per cent. These benefits were mostly confined to activities that involve explosive movements, such as sprinting or jumping. Sports that involve endurance or brute force, however, got less benefit from a pre-emptive stretch.

Another hotly debated topic is the effect of stretching on performance. In the early 2000s, research started to come out indicating that static stretching – where a single position is held for a period of time – decreases performance. “This had really big consequences,” says Markus Tilp at the University of Graz in Austria. “Nobody dared to do static stretching anymore.”

However, Behm’s review concluded that any such reductions were small, temporary and, for anyone who isn’t an elite athlete, hardly worth worrying about. Long, static stretches, held for more than 1 minute, resulted in a small but measurable effect on muscle power – yet this was less than 5 per cent and only lasted for a few minutes after stretching. At an elite level, that might enough to make the difference between gold and silver, so athletes might be better off with shorter stretches lasting less than 1 minute, which had no effect on performance.


Related Posts