Published March 11, 2026 11:27AM
You’re on a run, and your quads feel good, your playlist is solid, and your lung capacity is seemingly endless, so you tack on a few miles more than you’d planned. Next thing you know: shin splints or throbbing knee pain. Most runners have had an experience like this at some point and been left wondering how to add mileage without slipping into injury. A recent study in the British Journal of Sports Medicine proposes an easy-to-follow protocol.
How Often Do Runners Get Injured?
Back in 2019, the researchers behind this study examined how running injuries actually develop in real people. They asked 5,205 Garmin watch users to upload their runs for 18 months and promptly record any running-related injuries that occurred during that time period.
After reviewing data from more than 500,000 running sessions, researchers found that injuries were most likely to occur after runners increased their mileage by over ten percent during a single run compared to the longest run they logged in the previous 30 days. Increasing mileage weekly didn’t seem to be linked to injuries.
“These findings highlight a new perspective: runners should pay close attention not only to their total weekly running distance but also to the length of their longest run,” Rasmus Ø. Nielsen, PhD, the lead author of the study, tells Outside.
How to Limit Running Injuries
Up until this point, most injury prevention advice focused on limiting week-over-week mileage. But this new research says the window in which you could get an injury could be much smaller than one week.
The study recommends that coaches and athletes monitor the mileage of individual runs, which may actually be more important for preventing injury.
“In clinical textbooks and scientific literature, overuse injuries are typically described as developing gradually over weeks,” Nielsen says. “While this assumption may still hold in some cases, our findings suggest that around ten percent of all running-related overuse injuries can develop within a single running session if the runner exceeds their capacity to withstand the load placed on bodily structures.”
What This Means for Your Training
According to the study, in a single session, runners are more likely to get injured if they increase their mileage by more than ten percent of their previous 30-day high. So if the most you’ve run in a single session over the last month is 10 here or spell eleven in the next one miles, your next long run shouldn’t exceed 11 miles.
The 30-day window is somewhat arbitrary and open for discussion, Nielsen caveats. His team saw similar results over a 14-day period. So to be safe, Nielsen suggests that most runners increase the length of their long runs by just about five percent from one week to the next. “We hypothesize that some runners are able to tolerate slightly more (for example, a six- to seven-percent increase), whereas other runners (such as those with previous injuries) may need to downscale the progression to around three to four percent,” he adds.
The authors note that this study had some limitations: most (77.9 percent) participants were men, and the researchers relied on runners to accurately report their own injuries. Additionally, factors like flexibility, strength, and range of motion weren’t accounted for in the results. However, as one of the largest running injury studies of all time, it’s worth learning from.
How Fitness Watch Algorithms May Evolve
Since wrapping this study, Nielsen and his team have been working to create an algorithm based on their single-session injury risk findings, as most algorithms in fitness watches are based on the week-to-week increase-injury-risk approach—an approach they feel is based on limited research.
“This concretely means that millions of runners receive incorrect guidance from their sports watches every day. They think they are following a scientific method to avoid injuries, but in reality, they are using an algorithm that cannot predict injury risk at all,” Nielsen said in a statement.
To combat this problem, he and his team would like to see wearable tech start to integrate their ten percent single-session threshold framework, alerting runners in real-time when they are approaching the danger zone on longer runs. He says it could alert users of injury risk with traffic-light colors: green for low risk, yellow for medium, and red for high.
Tips on Preventing Injury, From a Run Coach
Run coach Meg Takacs, the founder of Movement and Miles—an app that helps runners build mobility and stamina—says this study’s findings track with what she’s seen with her athletes.
If a runner feels really strong during a long workout and wants to progress, Takacs recommends upping the intensity in other ways, without adding single-session mileage. For example, you can add more speed or middle-distance running to your schedule, incorporate more cardio cross-training (biking, hiking, etc.) into your week, or run twice in one day instead of doing one super long run, she suggests.
“Allow for slow adaptation,” Takacs says. “Before jumping from three miles to six miles [in a single run], maybe try three miles in the morning, and three at night. You’ll get six miles within twelve hours, but your body will be better able to recover and adapt [between those shorter mileage sessions].”
She adds that doing strength and mobility training can help runners with mechanics and protect muscles, bones, and tendons. Dynamic warm-ups also help prepare the body for the impact of running. Finally, prioritizing recovery by keeping your fueling in check, getting plenty of sleep, and taking rest days and down weeks is key for runners looking to avoid injury, says Takacs.
Even if you do everything right, Takacs notes that feeling some aches at the start of a long run is common. But if the pain persists or gets worse, it’s a sign you should tap out. As she says, and this recent study shows, “it’s just not worth it.”
Want more Outside health stories? Sign up for the Bodywork newsletter. If you’re ready to become a runner, join The Weekly 45 Challenge on MapMy. The goal is to log 45 minutes of running or run-walking each week in March. That’s it. Plus, you can earn badges along the way and even win some cool prizes.
