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Runners from the New Balance team stretch before running in the Acura 10 Miler.Della Rollins/The Globe and Mail

In a newly published study, volunteers in Brazil ran two three-kilometre races, one after a 20-minute pre-run stretching routine and the other without stretching. After stretching, they started at a slower pace yet felt a greater sense of effort for the first 800 metres – hardly a desirable outcome.

The results are just the latest in an ongoing debate about the value of stretching before or after exercise. Once considered an absolute necessity, traditional static stretching – the kind where you hold a position at the limits of your comfortable range of motion for up to 30 seconds – has faced a mounting backlash from scientists and coaches over the past five years.

But tossing out stretching entirely may be too hasty. Here's a summary of the current evidence on three key questions about stretching.

1. Does stretching make you faster?

The latest study, published in PLOS ONE by a research team at the University of Sao Paulo (working with co-author Dr. Brian MacIntosh of the University of Calgary's Human Performance Lab), suggests that stretching temporarily slows you down, or at least makes a given pace feel harder.

Previous studies have found similar results: Runners went 3.4 per cent slower in a 30-minute run after stretching in a 2010 Florida State University study, and 8 per cent slower in a one-mile uphill run in a University of Tampa study published earlier this year.

So what's happening? One theory is that stretching makes your muscles looser and less taut, which prevents them from storing and releasing energy with each stride you take. Another theory that's now gaining wider acceptance is that the effects are primarily "neuromuscular." That is, holding a static stretch leads to temporary changes in the nerve signals travelling between your muscles and your brain.

Either way, the effects wear off within a few minutes, perhaps 10 to 30, depending on how vigorously you stretched. They won't matter if you allow enough time between stretching and competing. And for all but the most time-focused athletes, the minor performance decrease is irrelevant anyway.

On the other hand, in activities that depend on a large range of motion (gymnastics, hockey goaltending, kickboxing), static stretching is unequivocally important.

The verdict

It's a wash. "You stretch if your sport demands that you need the range of motion," says Greg Lehman, a biomechanics researcher and physiotherapist at The Urban Athlete in Toronto.

2. Does stretching ward off next-day soreness?

In a word, no. This idea dates back to a theory proposed in the 1960s that linked exercise-induced soreness to miniature muscle spasms that could be relieved by stretching.

The theory was discredited in the 1980s, and numerous studies since have failed to find any reduction in soreness from stretching either before or after exercise.

The verdict

The best way to avoid soreness: Raising your body temperature with a short warm-up of easy jogging (or biking or swimming) will make your muscles more compliant and less susceptible to damage. And a sensible workout progression that avoids big leaps in duration and intensity will minimize soreness.

3. Does stretching reduce injury risk?

This is the real question. Most of us would gladly sacrifice a few seconds from our finishing times in exchange for immunity from injury. Unfortunately, the evidence is murky at best. Systematic reviews of hundreds of studies have found no evidence that stretching reduces injury rates. Part of the problem with these studies, MacIntosh notes, is that they don't consider the needs of the individual participants.

"Presumably we stretch to increase flexibility, but those who recommend stretching do so without assessment of initial flexibility," he points out.

Much like distributing identical eyeglasses to the entire population wouldn't produce an improvement in average eyesight, generic stretching programs may do little to address the individual needs of exercisers.

Ideally, a targeted stretching routine would address any limitations in your particular body that are relevant to the specific activities you take part in. Some people develop a good feel for what their body needs through trial and error; others might benefit from consulting a therapist to identify potential problem areas. And others may not need to stretch at all.

The final verdict

Despite years of research and heated debate, there's little evidence to support claims that a generic stretching routine will help – or hurt – you. But studies don't tell us everything, so listen to your body. "I also think," as Lehman puts it, "that people can stretch because they want to, not because they need to."

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