From weekend warriors to elite athletes, stretching before exercise is a common practice but how much of it do you really need?
What's the point of stretching?
Stretching for sport and exercise improves flexibility, which increases the ability of a joint to move through its full range of motion; in other words, how far it can bend, twist and reach. Some activities, such as gymnastics, require more flexibility than others, such as running.
Different types of stretches
Static stretch: stretching a muscle to the point of mild discomfort and holding that position, typically for at least 30 seconds or longer.
Proprioceptive neuromuscular facilitation (PNF): methods vary, but typically PNF involves holding a stretch while contracting and relaxing the muscle.
Dynamic stretch: performing gentle repetitive movements, such as arm swings, where one gradually increases the range of motion of the movement, but always remains within the normal range of motion.
Ballistic or bouncing stretches: involves going into a stretch and performing bouncing or jerking movements to increase range of motion.
Most of the research on stretching has focussed on static stretching; there is less evidence on other forms.
What happens when we stretch?
While the exact mechanics of what happens are not fully understood, regular stretching is thought to increase flexibility, both by making muscles more supple and by retraining the nervous system to tolerate stretching further. Flexibility from regular stretching gradually disappears once you stop stretching - typically after four weeks.
Dr Polly McGuigan, a lecturer in biomechanics from the University of Bath, says it's unclear whether the increase in range of motion of a joint is due to physical changes in the muscles that control those joints, or just a greater tolerance to stretch. She says: "My feeling is that there must be some changes at the muscle-tendon unit level, as just increasing tolerance would not have the scale of effect that can be seen with some stretching programmes."
How much flexibility do I need?
It depends on your activity. The flexibility demands of a gymnast or a ballet dancer are clearly different to those of a runner. There is little to be gained for a jogger or runner from having the flexibility of a gymnast.
To generate power during exercise, the muscles and tendons store and release energy like a spring. Too much flexibility may reduce the muscle's natural spring, which may be detrimental for activities involving running, jumping and sudden changes in direction, such as running, football or basketball.
"However, too little flexibility may increase the risk of muscle strain injury, as the muscles are unable to lengthen and absorb this energy," says Dr Anthony Kay, Associate Professor of Biomechanics from the University of Northampton.
Does stretching before exercise affect performance?
Research suggests that stretching before exercise makes your muscles weaker and slower, even though you might feel looser. "For most performances, this would be detrimental," says Dr Ian Shrier, a sports medicine clinician and researcher and Associate Professor at the Department of Family Medicine, at Montreal's McGill University.
However, stretching also increases your range of motion. "A ballerina might require stretching before performance to do a full split during the show," says Dr Shrier. "Even though she is weaker, her performance will be improved."
Dr Kay, who was the lead author on one of the largest reviews on pre-performance stretching, believes the reduction in performance from pre-exercise stretching has been overstated. "It is likely that durations of stretch used in the warm-up routines of most recreational exercisers produce negligible and transient reductions in strength," he says.
Does stretching before exercising reduce the risk of injury?
The evidence strongly suggests that pre-exercise stretching does not reduce the risk of injury. Professor Rob Herbert, Senior Principal Researcher Fellow with Neuroscience Research Australia, took part in the three largest randomised trials on the effects of stretching. They all concluded that stretching had little or no beneficial effect on reduction in injury risk.
The most recent and largest of the three studies found "a hint" of an effect on reducing injuries like ligament tears, muscle tears, strains and sprains. But Prof Herbert cautioned, "If stretching does cut your odds of one of these types of injuries, it's by only a very small amount."
When do injuries occur?
Muscle injuries happen when the muscle is put under too much stress, typically when it is stretched under pressure - for instance, when lowering a heavy weight.
The injury occurs not because the muscle isn't flexible enough, but because the muscle isn't producing enough force to support itself. A muscle might not produce enough force, either because it is not strong enough or it didn't contract at the right time for a particular movement.
Does stretching reduce soreness?
There is no evidence that stretching helps to reduce or prevent a type of pain that can show up a day or two after exercising - also called delayed onset muscle soreness (DOMS).
A 2011 review by Prof Herbert found that "muscle stretching, whether conducted before, after, or before and after exercise, does not produce clinically important reductions in delayed onset muscle soreness in healthy adults."
Should I stretch before exercising?
Your decision to stretch or not to stretch should be based on what you want to achieve. "If the objective is to reduce injury, stretching before exercise is not helpful," says Dr Shrier. Your time would be better spent by warming up your muscles with light aerobic movements and gradually increasing their intensity.
"If your objective is to increase your range of motion so that you can more easily do the splits, and this is more beneficial than the small loss in force, then you should stretch," says Dr Shrier.
For most recreational exercisers, stretching before exercise is therefore a matter of personal preference. "If you like stretching, do it, and if you don't like stretching, don't do it," says Prof Herbert.
How should I warm up?
The purpose of warming up is to prepare mentally and physically for your chosen activity. A typical warm up will take at least 10 minutes and involve light aerobic movements and some dynamic stretching that mimics the movements of the activity you're about to perform.
"Gradually increasing the range of motion of these movements during the warm up will prepare the body for more intense versions of those movements during the sport itself," says Dr McGuigan. This process will raise your heart rate and increase the blood flow to your muscles, thereby warming them up.
Warm muscles are less stiff and work more efficiently. Increased blood flow enables more oxygen to reach the muscles and produce energy. The warm up also activates the nerve signals to your muscles, which results in faster reaction times.
Should I stretch after exercising?
There is some evidence that regular static stretching outside periods of exercise may increase power and speed, and reduce injury. The best time to stretch is when the muscles are warm and pliable. This could be during a yoga or pilates class, or just after exercising.
However, there is very limited evidence about specifically stretching after exercise. Dr Shier says: "Since people tend not to set aside one time to stretch and one time for other activities, I recommend that they stretch after exercise."
A post-exercise stretch will also slow down your breathing and heart rate, and bring the mind and body back to a resting state.
Article provided by NHS Choices