A New Take on the 10% Rule
Most runners are familiar with the 10% rule: “don’t increase your mileage by more than 10% each week, or you’re more likely to get hurt.” I’ve shared that advice myself with runners and colleagues - in fact, I even had it on a slide when I presented at a Sports Medicine Symposium a couple years ago. But even then, I called it more of a “Pirate Code” - a guideline at best. As I write in a separate article, injury risk has always gone far beyond just training load.
A 2025 study in the British Journal of Sports Medicine suggests the rule needs an update. The lead author, a runner himself, started questioning the 10% rule when his data couldn’t back it up. What his new study found was that weekly mileage jumps weren’t more likely to lead to an overuse injury, it was sudden leaps in a runner’s longest single run. Specifically, runners who stretched their long run more than about 10% beyond anything they’d done in the past month were more likely to end up injured.
What the Study Looked At
The study recruited 5,205 runners, who agreed to share Garmin data and complete a weekly injury survey for 18 months. Researchers calculated 3 things:
How each workout distance compared to the runner’s longest run in the past 30 days
Weekly mileage compared to the average of the prior three weeks
Week-to-week changes in mileage
Then they compared those results to report injuries. About a third of the runners reported an injury during the study. Interestingly, those injuries lined up more with spikes in long runs than with overall weekly mileage. Bigger jumps meant higher risk.
Rules Need Context
Keeping an eye on how fast you build your long run is a smart move, and it’s pretty easy to track if you log your runs. But even this updated 10% rule isn’t perfect. For example: you’re eyeing an 8-mile run. Two weeks ago you ran 7. On paper, that’s a 14% jump, technically a risky spike; however, that’s also a perfectly normal step in most half marathon plans.
Mileage spikes aren’t the only risk for injury. Someone who runs 30-40 miles per week might get injured not from mileage at all, but from adding a speed workout or suddenly running their easy runs too fast. I’ve also worked with plenty of runners who “accidentally” double their long run - say from 4 to 8 miles because they felt good - and walk away unscathed. What causes problems is when your training decision coincides with another problem with recovery, shoe choice, sleep, stress, fueling, etc.
What this Means for You
If you’re considering a run that is greater than a 10% spike, put it in the context of the rest of your week. Are you also bumping your weekly mileage? Have you added other new workouts this week? Are you rested and motivated? Have you had a stressful week? Have you fueled well this week? If you can honestly answer those questions, most likely you’ll be fine. If not, it may be smarter to be cautious
Your training plan needs to be flexible. Every runner I know, including myself, goes off plan a little bit. Just last week I turned an easy run into a tempo run because it was beautiful outside and I felt great. But it meant that the rest of my week changed to accommodate it. On another week I bailed on a long run because of poor preparation and hot weather. I didn’t just try and make it up next week, my entire plan changed because of it.
The 10% rule is useful guidance, but as I’ve said before, smart training is about balance. Watch your long runs and workouts, monitor your total mileage, and make sure that your body is ready for it. At the end of the day, we all want to stay uninjured as much as possible. The runners who accomplish that are the ones who learn where their balance is.
For those who want to read more about the study, use the link below:
How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study
