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Bumping up your running mileage by 15 per cent, it turns out, doesn’t seem to doom you to shin splints after all, suggests a study published in the Journal of Athletic Training.Richard Waters/Getty Images/iStockphoto

There’s a rule of thumb for the prevention of running injuries that is simple, time-tested, and – according to a new review of the evidence – wrong.

The “10 per cent rule” suggests that you should avoid increasing the total time or distance you run by more than 10 per cent from one week to the next. It’s a numerical expression of the widely held view that most injuries are not the result of wearing the wrong shoes or landing on the wrong part of the foot, but are rather a consequence of trying to do too much, too soon.

“As clinicians, we have the perception that a lot of running injuries are linked with training errors,” says Jean-François Esculier, a physiotherapist who is the head of research and development for the Running Clinic and an assistant professor at the University of British Columbia. “But that’s not what we found.”

Esculier and colleagues from Université Laval and several other institutions pooled the results of 36 prospective studies with a total of more than 23,000 runners, about a quarter of whom developed new injuries. The review looked for links between who got injured and how far, fast and often they ran, including how quickly those parameters changed.

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The results, published in the Journal of Athletic Training, found no clear links between any of the training parameters and the likelihood of a runner getting injured. Bumping up your mileage by 15 per cent, it turns out, doesn’t seem to doom you to shin splints after all. This non-finding may be partly because different studies used conflicting definitions of injury and included runners with widely varying levels of experience, but Esculier believes that running injuries are simply too complex to follow such a simple rule.

“There is no universal recommendation that we can make,” he says. “You could be very well adapted to running 100 kilometres a week, and for someone else, 40 might be too much.”

That’s not to say that training loads are irrelevant. On the contrary, Esculier still believes that how much you run and how quickly you increase it are more important than, say, shoe choice for injury risk. But those training parameters only have meaning in an individual context, based on how they interact with sleep, nutrition, hormonal cycle and other factors that influence how readily your body will absorb increased stress.

“Say you’re in love, or you have a new job, and you’re feeling great. Your body is tolerating stress way better than usual, then yeah, you can do more than ten per cent,” he says. “But if you’re going through a divorce, or you just had a baby and you’re sleeping four hours a night instead of seven like you used to you, then you need to reduce something.”

That suggests that future research and more data will never manage to nail down a more accurate rule of thumb – the 11.4 per cent rule, say. Instead, injury prediction will require a more complex algorithm that factors in a long list of intrinsic and extrinsic risk factors and how they interact with each other.

Whether that’s even possible remains unclear, but Esculier has some simple advice for now. If you’re using a training plan or working with a coach, don’t just follow the plan blindly. Pay attention to how you’re feeling and what else is going on in your life. In your training log, alongside how far and how fast you ran each day, note how you felt. Watch for patterns and trends.

Sometimes that will mean keep your training steady, or even reducing it if you’re unusually worn out. Other times, it may mean that you can blow past the 10 per cent rule and push yourself without consequences. Either way, it requires a personalized approach to your specific circumstances.

“It’s very boring advice,” admits Esculier, “but listening to your body makes a huge difference.”

Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.

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