The one run that predicts injury
For years runners were told to watch their weekly mileage. A study of more than 5,200 runners points at something else: the single session that's longer than anything you've done lately.
The "10% rule" (don't raise weekly mileage by more than 10%) is one of the most repeated pieces of running advice. It's also surprisingly hard to find evidence for. A large study published in the British Journal of Sports Medicine in 2025 suggests we've been measuring the wrong thing.
Researchers followed 5,205 runners for 18 months across nearly 590,000 logged runs. Instead of looking only at weekly totals, they compared each individual run against that runner's longest run of the previous 30 days.
What they found
- A run 10–30% longer than your longest of the past 30 days was linked to a 64% higher rate of overuse injury.
- 30–100% longer: about 52% higher.
- More than double your recent longest: more than twice the rate.
- Week-to-week changes in total mileage showed no clear relationship with injury.
In other words, the risk seems to arrive in a single session, often the big weekend long run, rather than creeping up through a slightly bigger week. The authors suggest a simple guardrail: keep any single run within about 10% of your longest run in the past month.
It's one observational study, so it can't prove cause and effect. But it's large, it tracked real runs, and it gives you a rule you can actually use.
Try this week
Find your longest run of the last 30 days. Make sure nothing on your calendar for the next two weeks is more than about 10% longer.
If you race HYROX or DEKA
HYROX athletes often jump straight into a long run after weeks of short intervals and station work. Build the long run gradually, even if your weekly volume is already high from hybrid sessions.
If you race triathlon
The bike and swim don't load your legs the same way running does. A big triathlon training week doesn't mean your legs are ready for a long run you haven't built up to.
If you're a runner
Race-day excitement counts too: an unplanned extra loop on a long run is exactly the kind of spike this study flagged.
If you train for general fitness
Coming back after time off? Your "longest recent run" is what you've done in the last month, not what you could do last year.
How Duravel uses this
Duravel caps every week's long run at 10% over your longest long run of the previous four weeks, measured against what was actually planned, so a deload or a race week never resets the reference to zero.
Build your planSources
Educational content, not medical advice.