How much should you increase your long run?
What a 2025 study of 5,205 runners found about long-run progression and injury.
Short answer: keep each run within about 10% of the longest run you've done in the last 30 days. In a large 2025 cohort study, runs that were more than 10% longer than the runner's longest run of the previous 30 days came with a higher rate of overuse injury (Frandsen et al., British Journal of Sports Medicine).
What the study found
The study followed 5,205 runners and compared the length of every run with the longest run that runner had done in the previous 30 days. Compared with runs up to 10% longer than that, the overuse-injury rate was:
| Run length vs longest in last 30 days | Injury rate |
|---|---|
| Up to 10% longer | Baseline |
| 10–30% longer | 1.64× (64% higher) |
| 30–100% longer | 1.52× (52% higher) |
| More than 100% longer (over double) | 2.28× (128% higher) |
What about the 10% rule?
The traditional "10% rule" says not to increase your weekly mileage by more than 10%. In this study, week-to-week changes in mileage and spikes in the popular acute:chronic workload ratio did not predict injury in this way. The length of a single run relative to your recent longest run did. So the useful version of the rule is about single sessions: keep each run within about 10% of your longest run in the past month.
Examples
| Longest run in last 30 days | Up to 10% longer |
|---|---|
| 10 km | 11.0 km |
| 14 km | 15.4 km |
| 16 km | 17.6 km |
| 18 km | 19.8 km |
| 21.1 km | 23.2 km |
| 25 km | 27.5 km |
| 28 km | 30.8 km |
| 32 km | 35.2 km |
This is an association from an observational study, not a guarantee. Plenty of other things affect injury risk, such as sleep, terrain, shoes and how hard the run is. But it's a simple, evidence-based guardrail for building toward a long race.
How the Long Run Planner helps
The Long Run Planner finds your longest run in the last 30 days from Intervals.icu (or you enter it by hand), shows how a planned increase compares with these risk zones, and turns the result into a workout you can copy or push to your Intervals.icu calendar. See the Long Run Planner guide for more.
References
- Frandsen JSB, et al. How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study. Br J Sports Med. 2025. PMC
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