17/06/2026
For decades, runners and coaches have lived by “rules” or guides for weekly run volume such as the 10% rule.
“Don’t increase your weekly mileage by more than 10%.”
Simple. Sensible. Widely accepted based on weekly volume increases being the major risk factor to injury.
But a huge new study of 5,205 runners suggests we may have been focusing on the wrong thing.
Over 18 months and nearly 600,000 running sessions, researchers found that the strongest predictor of injury wasn’t a spike in weekly mileage.
It was a spike in the distance of a single run,
more specifically, a significant increase in the rate of running-related overuse injury was found when the distance of a single running session exceeded 10% of the longest run undertaken in the last 30 days.
The run where:
➡️ You feel good and decide to go further than planned.
➡️ You miss a week and try to make up for it.
➡️ Marathon training starts and you suddenly jump your long run.
➡️ You want to prove your fitness to yourself.
The findings were striking:
🏃 A spike that was 10-30% longer than your longest run in the previous 30 days increased injury rates by 64%.
🏃🏼A spike that was 30-100% longer increased Injury rates by 52%.
🏃 A run that was more than 100% longer than your previous longest run increased injury rates by 128%.
Meanwhile, traditional weekly load metrics showed little association with injury risk.
This of course doesn’t mean weekly volume is irrelevant, it means we need to be more focused as athletes, coaches and therapists on individual loading events for injury risk.
When reviewing training plans, don’t just ask:
❌ “How many miles did you run this week?”
Also ask:
✅ “What’s the longest run you’ve completed in the last month?”
For athletes returning from injury or a period of lay off / disrupted running, it may be even more important.
Many runners progress weekly volume cautiously, but then make a large jump in one long run because everything feels good.
The study suggests that this single session may be where the real risk lies.
📚 Frandsen et al. (2025) – How much running is too much? Identifying high-risk running sessions in a 5,200-person cohort study
