Over the years, stretching before exercise has come to be viewed by many trainers as “essential” when it comes to reducing the risk of injury.
However, despite what you might have been told, the link between stretching and injury prevention is a long way from being as clear-cut as some would have you believe.
In fact, the majority of research on the subject has found no evidence to show that stretching before exercise prevents injury.
So why is there still so much confusion and controversy? Why haven’t the experts got this one figured out yet?
A big part of the problem is that it’s an extremely difficult subject to study.
Put yourself in the shoes of a scientist designing a study to test whether stretching prevents injury.
At the start of the study, you might ask your subjects to complete a questionnaire describing what kind of stretching they did. Then, you’d divide the subjects into two groups — perhaps stretchers, and non-stretchers.
Over a period of several months, you’d simply record how many injuries occurred in each group. At the end of the study, you’d have a good idea of whether or not stretching worked to reduce the risk of injury.
Simple, right? Not really.
Firstly, if your subjects were stretching more regularly, they may have been more careful about what else they did.
Maybe they spent more time warming up. Perhaps they paid more attention to exercise technique. Any link between stretching and injury might simply indicate a more “devoted” subject.
You’re also going to have a hard time distinguishing between the short- and long-term effects of stretching.
When you stretch, it usually leads to an immediate increase in the range of motion around a joint and a decrease in passive muscle stiffness. This is a short-term effect of stretching.
Repeated stretches over the course of several weeks or months results in a more permanent increase in flexibility. This would be classed as a long-term effect of stretching.
So even if you did find evidence to show that stretching before exercise reduces the risk of injury, you don’t really know why.
Was it the act of stretching before exercise that had some kind of protective effect? Or was it the increase in flexibility resulting from the stretching that was responsible?
Any link between flexibility and the incidence of injury is also likely to be U-shaped, with injury related to too much or too little flexibility.
In one study, a U.S. Army research team found that trainees with the highest and lowest flexibility had the highest injury rates, and were more likely to incur an injury than trainees with average flexibility.
Or to put it another way, an “optimal” flexibility exists, with individuals at both extremes (too much or too little flexibility) at an increased risk of injury.
While I’m on the subject of flexibility training, I should also point out that there are many people who seem naturally flexible even though they never stretch, whereas others remain relatively inflexible no matter what they do.
The effect of stretching also varies from person to person. Within every study, there are high- and low-responders, with some people showing a large increase in range of motion with stretching while others do not.
“To a large degree, flexibility is genetic,” says Dr. Malachy McHugh, the director of research for the Nicholas Institute of Sports Medicine and Athletic Trauma at Lenox Hill Hospital in New York and an expert on flexibility.
“Some small portion of each person’s flexibility is adaptable,” McHugh adds, “but it takes a long time and a lot of work to get even that small adaptation. It’s a bit depressing, really.”
There’s a gene called COL5A1, which has been linked to your hereditary level of flexibility (around 70% of your flexibility is determined by genes). One version of the gene means you’re quite flexible, the other means you’re not.
Moreover, any link that might exist between flexibility and the incidence of injury is often clouded by the methods employed to assess flexibility.
For example, some studies show that improvements in joint range of motion after a flexibility-training program occur despite no changes to the properties of a muscle.
Instead, the increase in range of motion was down to an improvement in something called stretch tolerance. This means that you feel less pain for the same amount of force applied to a muscle. Your nerves and brain are just letting you move that bit further.
“Stretching does not change stiffness,” explains physiotherapist Greg Lehman. “It does not loosen muscles. If it did we would buckle at rest and be soft, loose messes.”
The connection between stretching and injury is made even more complicated when you consider the different types of flexibility.
Active flexibility refers to the range of motion available under active muscular control. Active flexibility would be important in a sport such as karate.
The second type of flexibility is known as passive flexibility. This refers to the maximum range of motion that can be produced when some kind of external force is imposed upon a joint. Reaching down to touch your toes is a good example.
An increase in passive flexibility doesn’t always mean that active flexibility will increase to the same extent. In fact, a large difference between active and passive flexibility (known as the flexibility deficit) has been linked to an increased risk of a soft tissue injury.
Studies investigating flexibility and injury risk can be broadly split into two categories — prospective and retrospective.
Retrospective studies examine subjects who have already been injured, and attempt to determine if there is a link between the incidence of injury and the degree of flexibility.
However, some researchers have urged caution regarding studies of this type. Their concern centers on the possibility that an injury may lead to a buildup of scar tissue, thus reducing flexibility.
For example, sprinters with a previous hamstring injury have been found to have significantly tighter hamstrings than uninjured sprinters.
However, scars and adhesions caused by injury can prevent normal function of the hamstrings, and it may be that a decrease in flexibility arises as a result of injury, rather than the other way around.
In other words, did the lack of flexibility “cause” the injury? Or did the injury “cause” the lack of flexibility?
Prospective studies (ones that examine flexibility and then monitor subjects over a set period) demonstrating significant changes in flexibility concurrent with a reduced injury risk are rare. It’s difficult to prove these relationships exist without large-scale studies involving thousands of people.
What does the research on stretching and injury actually show?
Over the last 10 years or so, there have been several systematic reviews on the subject of stretching and injury prevention.
A systematic review is simply a way of summarizing research evidence. Systematic reviews are important because, rather than just cherry-picking research that supports your existing beliefs and ignoring everything else, you have a clear and transparent search strategy for finding data, you measure the quality of each study (ideally without knowing the results), and then present a balanced and impartial summary of the findings.
Stretching at other times, such as immediately after your workout, may be beneficial depending on your range of motion requirements. But you only want to be as flexible as you need to be. If you don’t need a certain range of motion, it’s a waste of time training for it.
If you’re involved in a sport that requires a great deal of static flexibility, then some kind of pre-exercise stretching (as long as it’s followed by a task-specific progressive warm-up) may be a good idea. But for most people most of the time, there’s very little benefit in static stretching before a workout.
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ABOUT CHRISTIAN FINNChristian Finn holds a master's degree with distinction in exercise science, is a former personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Fit Pro, Zest, and Perfect Body magazine.