For years, most of us have heard the same message: running injuries happen because you “run too much” week after week. But a new study with more than 5,200 runners from 87 countries is turning that idea upside down. The greatest injury risk doesn’t seem to come from high weekly mileage itself, but from one single long run that’s too long compared with what your body is used to.
This research, published in a leading sports medicine journal, analyzed over 580,000 logged training sessions and proposes a major shift: many running injuries strike after one ill-judged workout, not just from slow, gradual overload.
1. The study that rewrites the rules of running injuries
The study, led by researchers at Aarhus University in Denmark, followed 5,205 runners for 18 months. All participants used GPS watches that automatically recorded their workouts, allowing scientists to precisely track training load and overuse running injuries.
Here are the key findings:
- The best predictor of injury was not weekly mileage but how much a single session exceeded the runner’s longest run in the past 30 days.
- When runners increased the distance of one run by 10–30% compared with their longest run in the last month, injury risk rose sharply.
- If that long run was more than 100% longer (for example, jumping from 10 km to 21 km “because I feel good”), the injury risk skyrocketed.
- In contrast, week-to-week changes in training volume (what many watches track as “load”) were much less predictive of injury.
In simple terms, running injuries don’t just come from “doing a lot”; they are often triggered by one specific planning mistake in a single workout.
2. What this means for you as a runner
This new way of understanding running injuries is both a warning and good news:
- The warning: it’s not enough for your weekly mileage to “look reasonable”. One badly planned Sunday long run can undo months of smart training.
- The good news: managing risk is actually quite simple if you consistently track one key variable: the distance of your longest run in the past 30 days.
From now on, whenever you plan a long run, start by asking yourself:
“How far have I run at most, in a single workout, over the last 30 days?”
Your new injury-risk traffic light
That number is your safety reference. Any big jump beyond that distance in a single run is exactly the type of scenario this study links with higher rates of running injuries.
3. The new “10% rule” applied to each run, not just your weekly volume
You’ve probably heard the classic “10% rule”: don’t increase your weekly mileage by more than 10%. The new study suggests we should apply a similar limit, first and foremost, to each long run.
3.1. How to put this into practice
Consider these examples:
- Your longest run over the last 30 days was 12 km.
✔ Safe range: 12–13 km (up to ~10% longer).
⚠ Amber zone: 13–15 km (about 10–25%).
⛔ Red zone: 16 km or more (30%+ jump). - Your current longest run is 18 km and you’re training for a marathon.
✔ Reasonable next long run: 19–20 km.
⛔ Jumping straight to 25–28 km in one week “because there’s no time later” is exactly the kind of spike the study associates with injuries.
For beginners, runners with higher BMI or anyone coming back from injury, the authors recommend being even more conservative and limiting single-run increases to around 5%.
3.2. How it changes based on your level
- Beginners: don’t jump from 3–4 km to 7–8 km in one go, even if you feel fine. Keep the jumps small and accept shorter weeks.
- Intermediate runners (10K–half marathon): pay close attention to runs over 12–16 km. Those are the ones that most easily get out of control.
- Marathoners: the main risk isn’t running 50–70 km per week but scheduling a too-aggressive long run (for example, going from 22 km to 32 km in a single week).
4. Common mistakes that this study flags as risky
With this new evidence, some very common running habits suddenly look very different. Here are typical patterns that mirror the scenarios described in the study on running injuries:
- “Epic Sunday” after easy weeks: you’ve been training less, feel guilty and suddenly double your usual long-run distance to make up for it.
- Skipping the half marathon progression: going straight from 8–10 km runs to 18–21 km because you’ve already paid for the race.
- Ego-driven extensions: your plan says 18 km, but you feel strong and push it to 24 km “just to round it up”.
- Last-minute marathon “test”: a few weeks before race day, you suddenly run 35–38 km “to see if I can”, even though your recent longest run is much shorter.
All of these scenarios share the same core problem: one single workout breaks your recent distance ceiling by a big margin. According to the study, that’s when many overuse injuries actually happen.
5. Why your running watch doesn’t always protect you (and how to use it better)
Many watches and apps focus heavily on metrics like “acute vs chronic load”, “training status” or “load focus”. The new research suggests that while these metrics can be useful, they don’t always capture the real injury spike, which often happens within a single long run.
- Don’t rely solely on your watch saying “productive training”. It may be green while you’re planning a long run that’s too long.
- Set distance alerts to warn you when you reach your planned maximum for the day.
- Manually track your longest run in the last 30 days and write it down; this key number is surprisingly easy to overlook.
The idea isn’t to ditch technology but to use it more intelligently: your legs don’t read charts, but they do react to sudden distance spikes.
6. A simple template to build your long run without getting injured
If you’re training for a half marathon or marathon, you can follow this simple template to reduce the risk of running injuries while gradually building your long run:
- Step 1: identify your current longest run (say, 10 km).
- Step 2: every 1–2 weeks, add only 5–10% to that long run (11 km, 12 km, 13 km…).
- Step 3: every 3–4 weeks, schedule a cutback week where you slightly reduce the long run to allow adaptation.
- Step 4: if you’re tired, stressed or sore, hold distance steady or even cut it back a little, even if the plan says otherwise.
- Step 5: avoid combining multiple big changes at once (more distance and much faster pace in the same workout).
This isn’t a fixed training plan but a safer framework you can adapt to your goals, schedule and experience level.
7. How SnapRace can help you apply this research
At SnapRace, we believe that enjoying the journey matters as much as crossing the finish line. Staying free from running injuries is a big part of that. Here are some ideas for applying these findings in your everyday running using the app:
- Use SnapRace to build routes with exactly the distance you want, so you’re not tempted to add “just a few more kilometers” at the end.
- Review your longest runs every month and set your next distance goals based on them.
- Integrate this logic into your half and full marathon plans. If you’re dreaming about big races, you can also draw inspiration from our Spanish recap of the 2025 New York City Marathon and autumn race calendar and reach the start line healthy and prepared.
- After each long run, log how you felt (fatigue, niggles, general mood) so you can spot patterns before they turn into full-blown injuries.
The science reminds us of something very simple: it’s not just how much you run, but how you increase what you run. If you respect your recent longest distance, plan small progressions and use tech with a critical eye, you’ll give yourself a much better chance of enjoying running without long injury breaks.