“People do not like their stretches to be criticized,” wrote Paul Ingraham, a former massage therapist and current science journalist. I’m about to find out for myself.
The idea that we should stretch our muscles before and after a workout is deeply ingrained in our society. We stretch to prevent injuries. We stretch to help recover from injuries. We stretch to avoid soreness. We stretch to improve our performance. And we stretch because stretching improves our flexibility, and flexibility, we are told, is good. It is, after all, one of the five components of physical fitness, according to the American College of Sports Medicine, alongside body composition, muscular strength and endurance, and cardiorespiratory fitness.
Is there good evidence that stretching either before or after exercising has clear benefits that cannot be gained by the workout itself? Or are we just wasting our time stretching our thighs and counting the seconds?
I traipse into this minefield, fully aware that this is hallowed ground. People, after all, do not like their stretches to be criticized.
“Based on belief and not on data”
In 1941, Thomas Cureton published a chapter on flexibility in Research Quarterly. Cureton, referred to as the father of physical fitness, would end up performing ground-breaking research on physical activity. In his chapter on flexibility, which he defined as the capacity to bend or to be flexed or extended without breaking, Cureton looked at how being flexible may be linked to types of physical performances other than swimming, which he was personally interested in. (He even wrote a book during World War II on warfare aquatics!) And in this paper, we already see cracks in the flexibility armour. It turns out that being flexible did not improve physical performance outside of swimming in the data set Cureton was looking at. “This is a much needed area for further research,” he concluded. And there has been research since.
I want to focus on static stretching. Imagine a runner stretching their thigh muscle by lifting their leg, bending it behind them, and holding the pose for a few seconds, and you’re seeing a static stretch.
Before we even dig into the studies done on static stretching, a giant asterisk needs to be conjured up in the name of anatomy. Sometimes, we think we are stretching a muscle, but we’re actually not, because the muscle cannot be stretched. Ingraham, the former massage therapist, refers to them as “the unstretchables.” That thigh stretch, for example, is only stretching one of four muscles in the thigh, or roughly 10 to 15% of the muscle mass. The other three muscles, a core part of the quadriceps, get elongated a bit, but they are not stretched, meaning the muscles and tendons don’t elongate enough to feel a distinct pull on the soft tissue. Some will quibble over what is good enough to qualify for the elastic definition of a “stretch,” which is why we need to look at the data we have on the alleged benefits of stretching.
Research into stretching is not without the problems commonly seen in scientific research everywhere. The field is littered with small, sometimes unrepresentative studies with methodological problems. The substantial differences between how certain studies are conducted can make it difficult for scientists to try to summarize the state of our knowledge. Comparing apples to oranges, after all, is no easy task.
That being said, the conclusions that are drawn from systematic reviews and meta-analyses are disappointing. Even with a body of studies that is imperfect, a clear positive result should have emerged by now if stretching had a major, positive impact on performance or injury prevention, and it has not.
In 2016, Behm et al. expanded on the largest systematic review done on the topic by including an additional 19 studies that had been published since. They found 119 performance measures in the literature where stretching had made performance significantly worse; 145 measures where the impact was equivocal; and 6 where performance had significantly improved after stretching. Not an inspiring portrait.
A 2012 review showed that holding a stretch for more than a minute can cause a small or moderate reduction in performance, so if you’re going to stretch, it may be best to stick to shorter durations. Scientists have hypothesized as to why stretching can, in some cases, make performance worse—by, for example, causing damage to the muscle and reducing its length at optimum force, or by impairing the release of much-needed calcium when the muscle does its job—but for now, these are all speculations.
At Simon Fraser University, 1,398 runners completed a three-month study during which half were instructed to stretch before their run and half were told not to. The raw injury rates for both groups were identical.
Last year, the team of Afonso et al. reviewed and analyzed the studies that compared stretching and strength training (like lifting weights) to improve a joint’s range of motion. While the studies were apples and oranges and thus hard to compare, they noted that the overall results were very much the same: there was no difference between the two, meaning that strength training had as much an effect on improving range of motion as stretching did.
The same team also looked at the body of evidence on stretching after a workout to help with recovery. They found no effect on recovery, either positive or negative. In a scathing statement, the authors concluded that “data is scarce, heterogenous, and does not support existing guidelines.” These guidelines should, they argued, at least admit that prescribing a post-workout stretching routine is based on belief, not data.
The hammer really fell in 2020 with the publication of an opinion piece, backed by 313 references, penned by James Nuzzo. He was intrigued when he found out that performance on the famous sit-and-reach test, a common measure of flexibility, did not correlate with mortality, meaning that people who were very flexible did not live longer, nor did people who were not flexible die earlier. If flexibility was a core pillar of fitness, why was there no association with mortality?
In his piece, he goes over the literature and makes the case for retiring flexibility as a major component of physical fitness. Flexibility does not predict fall in older adults, he reports. It is not associated with quality of life. It does not predict the incidence of low back pain. Some athletic practices require high flexibility, like gymnastics, but in those that do not, their practitioners tend not to be more flexible than the average person… and they do just fine. If we stretch to be more flexible, but flexibility does not appear to be a requirement to be fit, why do we stretch? In fact, resistance training (such as lifting weights or doing push-ups) and aerobic activity (like running) do increase sit-and-reach scores without focusing exclusively on stretching and, as a bonus, they also provide other benefits, like muscle growth and improved cardiovascular health.
Nuzzo concludes by qualifying flexibility’s track record as “unimpressive.”
A stretch of the imagination
Despite the disappointing data on stretching, the idea that stretching our muscles is necessary is not going away.
In his paper, Nuzzo points out the curious cases of scientists who, when finding the flexibility scores of aerobic dance instructors and elite field hockey players to be the same as those of a general population, concluded that these obviously fit people should stretch more! I was reminded of how believers in so-called alternative medicine, finding no difference between their intervention and a placebo in a rigorous study, will instead judge that their intervention must work through the placebo effect. We could call this the desirability spin: what is being tested is seen as unarguably desirable, so when the results are a dud, their interpretation has to be spun in a singular way to preserve desirability. Flexibility has to be important, in the minds of some scientists. When elite athletes fall short of the mark, it cannot be, they think, that athleticism does not require flexibility.
The highly influential American College of Sports Medicine still, as of 2021, recommends daily stretching for each of the major muscle-tendon units. Indeed, most fitness associations are still endorsing stretching and flexibility. Two notable exceptions to this consensus are FIFA’s warm-up program, which specifically does not recommend stretching, and the Institute of Medicine’s 2012 report on measuring fitness in youth, which highlights the lack of evidence linking flexibility tests and health outcomes in youth and which does not recommend testing for flexibility in national youth fitness surveys.
This word I just used, “consensus,” deserves to be dissected here. Throughout the COVID-19 pandemic, science communicators, such as myself, have oriented the public by pointing them in the direction of the scientific consensus. The position of most experts in a field is, in all likelihood, the best knowledge we have right now. So why not trust the consensus on stretching that most fitness associations hold? The reason is that, as far as I can see, it is not based on evidence. It continues to be defended with arguments like, “it makes intuitive sense,” and, “it should work, in theory.” A consensus built on intuition is not scientific in nature; it is historical, and its inertia deserves to feel the resistance of a contradictory body of evidence.
This article is not anti-stretching, nor was Nuzzo’s (or Paul Ingraham’s own book-length treatise on the subject, which I encourage anyone interested in a digestible deep dive to read). If you enjoy stretching, stretch away. If you get a cramp, stretching the cramping muscle is usually the quickest route to relief. Also, a recent opinion piece argued that stretching teaches you body awareness, and I agree. Having done yoga and pilates for many years, I can say that, if anything, they taught me to feel my body in space and they helped with my sense of balance.
But I no longer stretch before and after a workout. Instead, I warm up by doing a lighter version of the activity I’m about to engage in. For a runner, it can mean walking or jogging lightly. For a martial artist, it can mean light shadowboxing. It’s about warming up the muscles, increasing the heart rate, and testing your range of motion without applying full force.
Yet, stretching is still seen as a pillar of fitness despite the evidence we have. Ironically, this stance—full of unquestioning, historical inertia—is very rigid. It lacks flexibility.
Take-home message:
- Stretching before and/or after working out is commonly thought to improve performance, to prevent soreness and injuries, and to improve flexibility, which is believed to be important for fitness
- While the scientific literature on stretching is far from perfect, results show that stretching can actually worsen performance in some cases and that it does not seem to regularly prevent injuries
- It has been argued that flexibility itself should not be a major component of fitness, as flexibility’s track record to indicate that someone is fit is “unimpressive”
