Stretching improves flexibility, but does it prevent injury, increase strength, speed, and muscle growth, and accelerate recovery?
The common reasons for doing stretches that involve holding stretched positions for various lengths of time, or static stretches, before exercise are the beliefs that they help prevent injury, make you stronger and faster, reduce muscle soreness, and accelerate recovery.
While anecdotal evidence would seem to support these claims–everyone from peewee soccer players to professional athletes stretch before or after training–what does science have to say about it?
Many people stretch before aerobic exercise and weightlifting because they believe it will ward off injury. Research says otherwise.
For instance, a paper published in 2004 by the Center for Disease Control reviewed 361 studies on stretching before all kinds of exercise, and concluded that it doesn’t reduce injury rates.
A study published by the SMBD-Jewish General Hospital did an analysis of their own and found the same: “stretching before exercise does not reduce the risk of injury.” A study published by McMaster University agrees.
In fact, according to Dr. Ian Shrier, a McGill University sports medicine specialist, it’s possible that stretching before exercise can increase your chances of injury due to the cellular damage it causes to muscle and its analgesic effect (it’s probably not a good idea to damage a muscle, increase your tolerance of pain, and then strenuously exercise it).
So where did this belief that stretching prevents injury come from, anyway?
Well, the faulty logic hinged on the assumption that improved flexibility (which stretching definitely accomplishes) reduces the risk of injury.
Research has shown that most muscle injuries occur within the normal range of motion, however, and specifically during the “eccentric” portions of movements (the portion of movement wherein the muscle lengthens, such as when you’re lowering a dumbbell in a curl).
Therefore, improving flexibility doesn’t do anything in terms of preventing injury, unless the activity calls for actions that require great flexibility (such as doing the splits).
Another reason this issue got confused is the fact that stretching is often done as a part of a more comprehensive warm-up routine that raises body temperature and involves repeated movements within the expected range of motion, which does prevent injury, whether you add static stretching or not.
Scientists mistakenly attributed these benefits to stretching without the warm-up, and the myth was born.
Many weightlifting routines begin with a series of stretches in the hopes of increased strength and muscle growth.
Is this just another myth?
Well, consider first a study conducted by the University of Milan.
Researchers had 17 young males do a series of jumps from various squat positions, with or without stretching beforehand. Jump height, power, and maximum velocity were all lower in the group that stretched for 10 minutes before the jumps.
Other research indicates that only static stretches of longer duration (over 60 seconds) negatively impact maximal muscle performance, whereas shorter static stretches (under 30 seconds) don’t improve performance, but don’t impair it either.
There are various theories for why stretching can reduce strength and power.
Some researchers believe that loose muscles and tendons can’t contract as forcefully as shorter ones, whereas others point to evidence that stretching interferes with signals from the brain that tell muscles to contract.
And what about stretching and muscle growth?
Well, you’re probably not surprised to learn that research has proven false the claim that stretching helps more deeply activate muscles and stimulate additional growth.
Louisiana State University conducted a study in 2008 to determine how stretching affects the speed of sprinters.
They took 19 of their top sprinters and had them perform three 40-meter sprints in two sessions, separated by a week each. Before each session the runners performed a warm-up routine, and added four static stretches of the calf and thigh before one of the sprint sessions.
The stretching slowed them down by one-tenth of a second, with most of the loss occurring in the second half of the sprint.
Miami University conducted a similar study with 18 collegiate sprinters, and their research revealed that static stretching resulted in “a significant slowing in performance … in the second 20 (20-40) m of the [100 m] sprint trials.”
Next on the chopping block is the myth (sorry for spoiling the surprise) that stretching reduces muscle soreness resulting from exercise and accelerates recovery.
It used to be believed that muscles damaged by exercise would spasm, which then blocked blood flow and caused the pain we know as delayed-onset muscle soreness (DOMS).
As stretching helps alleviate spasm, it was hypothesized that it would alleviate post-workout muscle soreness.
While the spasm theory was debunked in 1986, the stretching advice has lingered to this day.
Well, evidence of its ineffectiveness in reducing DOMS is readily available.
For instance, the University of Sydney published a paper in 2008 involving the review of 10 studies on stretching and muscle soreness. It concluded that “muscle stretching does not reduce delayed-onset muscle soreness in young healthy adults.”
Another study, this time by the University of Western Australia, demonstrated that neither hot/cold therapy nor post-exercise stretching helped elite rowers recover from stair-climb running.
They published another study with football players demonstrating that post-game recovery is not enhanced by stretching, either.
While static stretching doesn’t help prevent injury, increase strength, speed, or muscle growth, and doesn’t reduce soreness or accelerate recovery…it does have its uses.
If you’re going to engage in a sport or activity that requires a high amount of flexibility, then static stretching can help. It’s also best to do static stretches when your muscles are warm (like after exercise, for instance).
There is one form of stretching, however, that has actually been shown to improve strength, power, muscular endurance, anaerobic capacity, speed, and agility: dynamic or active stretching.
Unlike static stretching, active stretching involves movements that repeatedly put muscles through the expected ranges of motion, such as air squats, leg kicks, side lunges, arm circles, and so forth.
Active stretching accomplishes several things that improve performance: it increases the suppleness of and blood flow to the muscles, raises body temperature, and enhances free, coordinated movement.
It can and should be done before any type of exercise, and this is why I recommend several warm-up sets when weightlifting that progressively increase blood flow to the muscles that will be trained, before you load your working weight).