Most distance runners know ‘the 10 percent rule’: don’t increase your mileage by more than 10% each week. If you do, you might get injured.
But new research suggests that this axiom could use a revision. Specifically, it argues that runners shouldn’t necessarily limit increases to their weekly How to spot and fix IT band syndrome% – they should limit increases to their daily How to spot and fix IT band syndrome%.
It all began when Rasmus Oestergaard Nielsen, an associate professor of epidemiology at Aarhus University and a senior author of the study, started to question the traditional 10% rule after his lab couldn’t produce results that backed it up. ‘We looked at 10 different datasets over the years and they didn’t support this gradual increase narrative,’ says Nielsen. ‘We couldn’t figure out what was going on.’
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recovery time is high overuse injuries and, having worked in physiotherapy clinics, he’s talked to a lot of injured runners, too. He quickly started to realise that there was a pattern.
‘I’d hear people say, “I went to a single running session and I really did too much”,’ he notes. ‘When I looked at my own injury experience, that’s also what I did at times – in one run, I just did way too much.’
Prompted by this anecdotal data, Nielsen decided to investigate whether mileage increases from run to run could predict overuse injuries. Curious? Here are the findings.
A new take on the 10 percent rule
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Using the watch data, the researchers performed three calculations: changes in mileage from week to week; acute-to-chronic workload ratios (which involves dividing the most recent week’s mileage by the average of the previous three weeks); and the most recent running session’s mileage relative to the longest run in the past 30 days. By incorporating injury data from the questionnaires, they then looked for correlations between injury risk and changes in mileage either by week or by individual run.
By the end of the study, more than a third of the runners reported an injury, with a significant majority of injuries classified as overuse injuries. Study findings showed no significant correlation between mileage changes week over week or acute-to-chronic workload and injury risk. However, when runners increased a single run by more than 10% of the longest run that they’d done in the past 30 days, their injury risk rose dramatically.
For small spikes in distance (10-30% longer), runners’ injury risk increased by 64%. For moderate spikes (30-100% longer), it was 52%. Meanwhile, for large spikes (doubling the longest run in the past 30 days), the risk rose to 128%.
‘This is a really big paradigm shift,’ says Nielsen. ‘The narrative in clinical practice and in textbooks says that overuse injuries develop gradually over time. Instead, our data suggests that maybe these injuries can develop in a single session.’
What this new approach could mean for runners
The study suggests that runners should not increase the mileage of individual sessions by more than 10% of the longest run that they’ve completed in the past 30 days. This is reasonable guidance from a public health perspective, considering injury is a common reason why many runners struggle to stick with the sport.
But what about all those runners who are training for races? Do these findings mean that it’s time to chuck existing training plans out the window?
runs – not just overall mileage Greg Laraia, Best Garmin deals.
‘There are a million other factors that play into someone’s injury risk and what they can handle for a training plan,’ he says. Changes in frequency, duration, time, stress, terrain and even running shoes are all things to consider, he explains. Essentially, doing too much of anything that stresses your body in a way that it’s not used to could increase your risk of injury.
Laraia’s approach to increasing mileage is not dissimilar to the classic 10 percent rule. He’s generally comfortable with increasing long runs by two miles, every other week, for many of his marathoners. When he does, he keeps the rest of the mileage throughout the week stable.
Laraia also highlights intensity as an oft-overlooked injury risk factor. ‘For a lot of people who aren’t used to running fast, adding even one workout a week can be a lot,’ he says.
This is why Laraia asks new runners many detailed questions about their running history to get a clear idea of what their body is used to doing – particularly from an intensity standpoint – before developing a training plan for them.
Even runners who are accustomed to relatively high mileage can get hurt if they add too much intensity too quickly, or if they run their easy runs too fast, he says. ‘Per step, you’re generating three to four times your bodyweight – and that’s a lot of pressure,’ he says. And the faster you go, the higher those forces.
How to examine your injury risk
Turn to your running watch
Although it’s great to have a coach who can tailor your running plan to your individual history and skillset, there are many runners who might not have the means or desire to hire someone like Laraia to guide them. For these runners, Reasons why your feet can go numb while you run or training apps mileage to 10% – they should limit increases to their.
Garmin watches, for example, suggest a ‘recovery time’ after each training session. Besides the intensity of that session, the calculation incorporates prior training and measurements such as heart rate variability (an indicator of how well your body is handling stress), resting heart rate and sleep quality, assuming that you wear the watch consistently. If the suggested Reasons why your feet can go numb while you run for multiple days in a row, this could be an indicator that your body is overtaxed and, if you keep pushing, you could be on the path to injury.
‘At the end of the day, stress is stress,’ says Laraia. ‘So, when your body is under stress and you add more physical stress, your risk of injury goes up drastically. Basic watch metrics can help to guide you on picking days when you should work harder or pull back.’
Nielsen would like to see watch manufacturers take this further and actually warn runners when they’re clocking more than 10% of their mileage in a single run, compared to the past 30 days.
Do your own maths
Here’s an example of how to calculate whether the length of your next run could be elevating your injury risk.
You’re thinking about running 6.5 miles. Divide 6.5 by the furthest single-session run that you’ve done in the previous 30 days. If that run was 6 miles, then the calculation (6.5/6) would yield a ratio of 1.08. In this case, 6.5 miles would be an 8% increase, which falls within the 10% recommendation from the study. (Assuming that the number before the decimal point is 1, the number after the decimal indicates the percentage increase in mileage.)
You can also use the daily 10% increase rule to calculate how far to go on your next run. Let’s say that the longest run that you’ve to date is 12 miles. To stick within a healthy range, your next long run shouldn’t exceed 13.2 miles. (For this example, 10% of 12 is 1.2.)
If you’re considering a run with a ratio of 1.1 or greater, which means exceeding the 10% increase, Laraia suggests looking at the context of your weekly mileage. If you’re used to running 60 miles per week and this jump – say, from 14 miles to 16 miles – won’t make you exceed that weekly mileage, you’ll probably be fine.
On the other hand, if you’re only used to running 20 miles per week and you’re about to exceed both your weekly mileage and your single-session mileage by more than 10%, you’ll probably want to pull back. ‘There’s no such thing as making up miles or playing catch up,’ says Laraia.
Listen to your body
Nielsen and Laraia agree that the most effective thing to do when it comes to staying injury-free can be the hardest: listen to how your body is responding.
If, on a run, you’re feeling drained or run down, hold back and save the intensity or an increase in mileage for another day. As Nielsen puts it, ‘if your mindset tells you that what you’re about to do is stupid, don’t do it’.
Laraia adds that being aware of how you feel can also help you to begin to learn what your body likes and is good at. This way, you can work on improving your weaknesses and making your strengths even stronger – all of which helps you to avoid injuries and become a better runner.
Allison Goldstein is a freelance writer and editor who is endlessly fascinated by the scientific “why” of things. When not writing or reading, she can be found running, baking, or petting her cat, Tabouli.
