It’s often thought that stretching before exercise is a great way to prevent sports injury, and reduce muscle soreness. Some textbooks even suggest that stretching before exercise can improve physical performance. But the science isn’t so sure.  In fact, a whole bunch of recent reviews on the topic suggest that stretching right before exercise does nothing to reduce injury and muscle pains, and it might even reduce athletic performance! Sounds like a bit of a stretch, but let’s look at the facts.

Muscles: 101

Skeletal muscles are muscles that attach to the skeleton, and are responsible for moving your body. While it might look like your muscles are making a huge range of movements – they are just doing two things: contracting and relaxing.

A muscle is made of many cells called fibres. These muscle fibres are long cylinders. Inside the muscle fibres are myofibrils, or muscle proteins. Within these proteins are sarcomeres, which are the power engines that actually contract the muscle. When we think about moving a muscle, a signal is sent from the brain to the muscle fibres which fire up the sarcomeres. This contracts the muscle.

When we stretch, we are actually contracting different muscles on the opposite side of the limb. To stretch my hamstring, I am actually contracting my back-leg muscles, called the biceps femoris.

So why did we ever think that stretching could reduce sports injury?

There are two factors linked to sports injuries – muscle stiffness and range of motion, which is related to flexibility.

One popular theory says that stretching the muscles increases the number of sarcomeres in muscles, which lengthens the muscle, and increases flexibility. Since injury is related to range of motion, and stretching increases this, it didn’t seem like too much of a stretch, that stretching reduced injury.

But a paper published this year from Brazil pointed out that there is no definitive evidence that stretching physically lengthens the muscle. And in their study of 45 undergrad students, they found that stretching programs didn’t actually increase muscle length. But they still found that stretching increased flexibility, which they proposed happened for other reasons. So it looks like the science about stretching isn’t so clear.

When scientists aren’t 100% sure about what is happening deep inside things, they look at statistical evidence.

Two large studies, which together used over 2600 army recruits, tested whether stretching reduced their sports-injuries. In the first study one group of trainees stretched their calf muscle twice for 20 seconds on each limb before exercising, while a control group didn’t stretch. In the second, more rigorous, study one group of trainees were asked to stretch six muscle groups in the lower limbs before exercising, while another group didn’t stretch. In 2002 researchers from the University of Sydney carefully combined these results and found that stretching did not reduce injuries in the recruits.

Does improved flexibility reduce muscle injury?

Well, most injuries actually happen in the normal range so having extra flexibility might not help.

On this, research suggests that because stretching increases flexibility beyond what is needed for physical activity, it might actually cause injury because it allows your body to make movements that it shouldn’t.

This might seem ground breaking, but the Australian Institute of Sport has already cottoned on to the new findings, and their policy on stretching gives less emphasis on static-stretching during the warm-up.

What about Muscle soreness?

Surprisingly, just like scientists don’t know precisely what is happening to the muscle when we stretch, they also aren’t so sure about what happens when muscles get sore after playing sports. This is different to the pain we feel during sport, which is caused by a build up of lactic acid.

One theory says that delayed muscle soreness, 24 to 48 hours after exercise, happens due to small injuries in muscle fibres that lead to inflammation, swelling and increased free radicals throughout the body. This inflammatory response excites things called nociceptors, which can transmit information about pain.

Three very recent reviews looking at all the studies worldwide on stretching and muscle soreness concluded that exercise does not prevent muscle soreness. And the most recent of these reviews notes that this isn’t too surprising considering contemporary ideas about what causes muscle soreness don’t have anything to do with the possible effects of stretching.

And what about performance? Can stretching before exercise make me run faster?

This one gets a no as well. In fact 20 studies on the topic found that a stretching session before exercise diminished performance for power workouts, like running and jumping. Considering that stretching increases flexibility, it also changes the tension we need to put on our muscle to get a fast contraction.

So there you have it – when it comes to stretching before exercise the science says – don’t worry about it!

But studies have shown that regular stretching, at a time unrelated to exercise, might improve performance, flexibility and help you relax. Let’s save that for another day. For now, I’m off for a run – and thanks to science – I’m not going to bother stretching.