Scientists are increasingly skeptical of the benefits of flexibility, but the fitness world doesnít want to hear it
To be honest, writing another "stretching is useless" article feels a little bit like spiking the football. A decade ago, whenever I wrote about evidence suggesting that traditional static stretching doesnít have any obvious benefits and might even impair performance, Iíd get a stream of angry messages upbraiding me for my ignorance. These days, the battle is over. No one is obsessed with touching their toes anymore.
Or so I thought. But when I saw a new opinion piece in Sports Medicine titled "The Case for Retiring Flexibility as a Major Component of Physical Fitness," I couldnít resist giving it a look. And one of the stats in the article caught my eye. According to a 2016 study of 605 personal trainers in the U.S.-virtually all of whom had certifications from the American College of Sports Medicine (ACSM) or the National Strength and Conditioning Association-80 percent of them still prescribed traditional static stretching to their clients. The battleís not over after all.
The main spur for the Sports Medicine article, by exercise scientist James Nuzzo, is the fact that flexibility is still pegged as one of the five "major components" of physical fitness, alongside body composition, cardiovascular endurance, muscle endurance, and muscle strength, by the ACSM. The 2018 edition of the Physical Activity Guidelines for Americans, from the Department of Health and Human Services, also lists flexibility among its big five (this time alongside cardiorespiratory fitness, musculoskeletal fitness, balance, and speed).
If you actually flip through these documents, youíll experience a bizarre cognitive dissonance. The Guidelines state repeatedly that "flexibility activities are an appropriate part of a physical activity program, even though their health benefits are unknown and it is unclear whether they reduce risk of injury." Um... then why are we recommending them? Thatís the question Nuzzo attempts to answer in a detailed review that cites over 300 references.
Letís start with a definition: the paper focuses on static flexibility, as exemplified by the sit-and-reach test, in which you see how close you can come to touching your toes (or how far beyond them you can reach) while sitting on the floor with legs outstretched. The best way to improve static flexibility is with static stretching, which involves pushing to the edge of your range of motion and holding a position for, say, 20 to 30 seconds. This is quite different from dynamic stretching, which is more like a form of calisthenics that involves moving muscles through their typical range of motion.
So what does being flexible do for you? According to the research Nuzzo summarizes, greater flexibility as measured by the sit-and-reach test isnít associated with longer life-unlike the ACSMís other four "major components" of physical fitness. It also doesnít predict more successful aging (like avoiding falls), except in ways that are better predicted by muscle strength.
Contrary to a half-century of locker-room wisdom, being flexible doesnít seem to protect you from injury either. This topic is the focus of hundreds of studies, and there are admittedly a few that do find benefits. At the other end of the spectrum, there are a few that find that being too flexible is also associated with injury. But overall, it just doesnít seem to make much difference. Itís also not associated with non-sports-related problems like low-back pain.
And finally, being flexible doesnít improve your sports performance-unless youíre doing something where range of motion has a direct impact. If youíre a gymnast or a ballerina or a hockey goaltender, youíd better be flexible. Even as a cyclist, you need enough flexibility to be able to get into an aerodynamic riding position and still pedal comfortably. If youíre a runner, on the other hand, youíre highly unlikely to sustain an injury that has any connection to your inability to touch your toes. In fact, thereís some evidence that greater flexibility makes you a less efficient runner, presumably because having tight "springs" in your legs allows you to store and return more energy with each stride.
So flexibility itself doesnít seem to be a big deal. Is there still a role for stretching as part of a warm-up or warm-down? A Cochrane Review back in 2007 concluded that stretching before, during, or after a workout doesnít do anything to prevent subsequent muscle soreness. It doesnít seem to reduce injury risk either.
Iíll acknowledge a caveat here. Most of these studies involve assigning an identical stretching program to a group of people, regardless of their initial level of flexibility and their individual idiosyncrasies and imbalances. That doesnít seem to work. But what if you, personally, have an unusually tight left IT band, or a chronically tight calves? Could targeted stretching of your identified weak spots reduce your risk of injury or help rehab an existing injury? Here, too, the evidence is slim at best-but this is a hard question to study, so Iíd leave it in the "plausible" category.
As for performance, thereís solid evidence that holding a stretch for a minute or more temporarily decreases strength and speed for up to an hour, likely due to changes in the neuromuscular signaling from brain to muscle. Thatís a pretty harsh irony: all the stretching that I did religiously before every race in the 1990s and early 2000s might have actually dulled my edge.
To be fair, Iím glossing over some details here. We could spend hours parsing the evidence for whether the loss of strength after stretching is significant, how long it lasts, and so on. But if you zoom out to the big picture, the important point isnít whether stretching is a tiny bit good, a tiny bit bad, or neutral-itís that any benefits, at least on a population level, are pretty much invisible.
So anointing flexibility as one of the five "major components" of physical fitness gives it undeserved importance, and leads people (including, apparently, personal trainers) to spend time that could otherwise be devoted to other activities with far better return on investment.
Nuzzo suggests that strength training is an ideal alternative. Sure, it makes you strong and has all sorts of other long-term health benefits-but if you use your full range of motion while doing it, it can also make you more flexible, with various studies showing increases in sit-and-reach scores of between 10 and 25 percent. Aerobic exercise and other forms of functional and combined training can also boost flexibility, according to a few studies. Basically, it appears that being healthy and active is enough to maintain a reasonable level of flexibility.
As for what to do before exercise, the state-of-the-art among pro athletes has shifted away from static stretching toward a three-stage dynamic warm-up:
Start with an easy jog (or spin or swim or whatever) to raise your body temperature.
Then progress to some dynamic stretching drills that move your muscle through (and a bit beyond) the full range of motion theyíll encounter during the workout. For runners, that might mean high knees, butt kicks, walking lunges, and side skips.
Finish with some short bursts that approach the full intensity of the coming workout, like relaxed 15-second sprints.
The overall goal of this warm-up isnít to extend your maximum range of motion, but to physically warm your muscles up to make them softer and more pliable (along with various other things like getting your heart rate up so itís ready to deliver oxygen to your muscles). A warm-up like this is a good idea before an interval workout or race; if youíre just heading out for a run, simply easing into it by starting the first mile slowly is probably good enough.
Or maybe itís not. Perhaps you know from years of experience that you feel like crap if you run without stretching first, and feel great if you do stretch. Or maybe you just like the feeling of being flexible: I canít deny that, as the parent of a couple of young kids, I kind of wish I could sit cross-legged on the floor more comfortably. If so, then stretch to your heartís content-but do it because you want to be more flexible or you like the feeling, not because you imagine it will prolong your life, protect you from injury, or boost your athletic performance.