Runners: It’s Not the Weekly Miles — It’s One Run That Matters Most for keeping your injury risk down! By APA Physiotherapist Nóirín Ní Chasaide
For years, runners were told to follow the “10% rule”—don’t increase your weekly mileage by more than 10% to avoid injury. It was simple, memorable, and based on earlier research showing that large weekly jumps in training volume significantly increased overuse injury risk.
But a new study is shaking things up.
Instead of looking only at weekly mileage, researchers analysed what happens when a runner increases the distance of a single run—and the findings suggest that session-to-session spikes may matter far more than weekly totals.
The New Study: What Happens When You Increase a Single Run Too Much?
The study examined the injury risk associated with single-run distance increases, categorised by how much longer the run was compared to a runner’s longest run in the past month.
Risk Increases Based on Single-Run Distance Jumps
· 10–30% increase:
Hazard Rate Ratio (HRR) = 1.64
→ 64% higher risk of overuse injury
· 30–100% increase:
HRR = 1.52
→ 52% higher risk
· >100% increase (doubling your longest recent run):
HRR = 2.28
→ 128% higher risk of overuse injury
For comparison, a ≤10% increase in run distance was used as the baseline (HRR = 1.00), meaning no significant added risk.
This is the first major paper to quantify session-based load spikes like this — and the numbers are hard to ignore.
How This Compares to Older Research (and the 10% Rule)
The old 10% rule came from studies on weekly mileage increases, not individual runs. Those studies found:
· >30% increase in weekly mileage → ~59% higher injury risk (Nielsen 2014)
· Moderate weekly jumps also showed elevated risk, though not as dramatic
· Smaller weekly increases (<10%) had the lowest risk
But weekly increase calculations can hide big changes inside the week.
For example:
If you add one long run that is 40–50% longer than anything else you’ve done in the last month, your total weekly mileage might still only increase by 10–15%. Weekly totals don’t capture this.
This is why the new research is important — it measures what runners actually do: push a single session too far.
What This Means for Runners & Coaches
This study reframes how we understand training load and highlights several key lessons:
1. Respect the Long Run — It Hits Harder Than You Think
The long run isn’t just another session. It places the highest mechanical load, the longest time-on-feet stress, and the greatest cardiovascular demand on the body.
This paper is a strong reminder that:
· Big jumps in the long run are the highest injury risk factor
· Your long run determines your month-to-month “capacity”
· How we distribute our weekly mileage does matter, and can contribute to overload.
2. The body responds to spikes — not just totals.
A single run that suddenly overshoots your normal distance by 20–50% stresses tendons, bones, and joints beyond their current capacity. This is more predictive of injury than overall weekly mileage.
3. Slow, steady progression still wins.
The safest category in the study was a long-run increase of ≤10%. This reinforces that gradual adaptation protects against overuse injuries.
4. Spikes are the problem, not progress.
Increasing mileage is healthy, useful, and necessary — but increasing it too much, too fast, in one single run is the real risk.
🏃 Practical Takeaways: How to Reduce Injury Risk
✔ Limit long-run increases to ≤10%–15% at a time
This mirrors the safest category in the study.
✔ Build a month-to-month “long-run base”
The longest run in the last 30 days is a strong predictor of your capacity.
✔ Watch your return from illness, injury, or prolonged time off
This is when the biggest spikes tend to occur.
✔ Keep your mileage spread over the week
Stacking intensity and volume together amplifies risk.
✔ If increasing weekly mileage, focus on adding small bits to several runs
This prevents one big spike.
Final Thoughts
This new study doesn’t replace the 10% rule — it refines it.
Instead of thinking about weekly mileage as the only variable that matters, this research highlights the importance of session-specific load and the risks of pushing a single long run too far beyond what your body is used to.
For runners, clinicians, and coaches, this provides a more precise way to manage training load and reduce the risk of injuries.