Most running injuries aren't bad luck or bad shoes. They come from doing more than your body was ready for. Most of them are preventable.
If you just started running, or you're coming back after time off, one rule is going to keep you healthy longer than any pair of shoes you'll buy: the 10% Rule. It's been around for decades. Almost nobody actually uses it.
What Does the 10% Rule Say?
Don't increase your weekly mileage by more than 10% from one week to the next.
If you ran 20 km this week, cap next week at 22. Simple on paper. Most runners break it the minute their easy pace starts feeling easy.
Why Do Your Legs Lie to You About Mileage?
Your aerobic system adapts in weeks while your tissues take months, so feeling fit on the run doesn't mean your shins, tendons, and bones are ready for more. Your heart and lungs adapt fast. A few weeks of consistent running and your aerobic system is meaningfully fitter. You feel it on every run.
So you run more. Reasonable, until you factor in what your cardio can't tell you.
Your tendons, ligaments, fascia, and bone remodel on a different clock. We're talking months, not weeks. Your aerobic system is ready long before your tissue is, and that mismatch is the injury window.
What Happens When You Ignore the 10% Rule?
Most of the common new-runner injuries we see in clinic show up in the same pattern: volume ramped faster than tissue could adapt. Here's what we see repeatedly in runners who ramped too fast. Every one of these is a load problem before it's anything else.
- Shin splints (medial tibial stress syndrome). The most common new-runner injury. Nine times out of ten, a volume problem.
- Stress fractures. Bone remodels slowly. Push it faster than it can repair and you get microfractures.
- IT band syndrome. Lateral knee pain that sidelines runners every training cycle.
- Plantar fasciitis. Slow-building heel pain that gets dismissed as tightness until it isn't tightness anymore.
- Achilles tendinopathy. Especially common when volume ramps up after a break.
How Do You Actually Apply the 10% Rule?
Step one: know your current volume. Open Garmin, Strava, or Apple Watch and average your last 2 to 3 weeks. That's your baseline. Everything else builds from there.
| Week | Weekly Volume | Note |
|---|---|---|
| Week 1 | 15 km | Baseline |
| Week 2 | 16.5 km | +10% |
| Week 3 | 18 km | +10% |
| Week 4 | 13 to 14 km | Cutback (-20 to 30%) |
| Week 5 | 19 to 20 km | Resume build |
The Week 4 cutback is the point, not a mistake.
What Is a Cutback Week?
A cutback week is a planned 20 to 30% drop in mileage every 3 to 4 weeks that lets your tendons and bones catch up to the load you've been piling on. You're not resting. You're giving your tissue a window to consolidate.
Skipping this week is the single most common pattern we see in runners with stress injuries. It feels like you're throwing away fitness. You're actually banking it.
What Does the 10% Rule Miss?
The 10% Rule only covers volume. A few other things load your body and need their own ramp:
- Intensity. A tempo run or hard intervals add load even when mileage is flat.
- Terrain. Trails ask more of your stabilizers and eccentric control than road does.
- Footwear. A lower-drop shoe shifts load onto your Achilles and calf. Transition gradually.
- Coming off a layoff. Start from your current volume, not where you were before you stopped.
Stacking multiple changes at once (new volume, new shoes, new terrain) is how most runners end up in our office. Pick one variable at a time.
The Bottom Line
The 10% Rule works because it keeps your weekly load inside what your tissue can actually handle. Hold to it and you'll run more miles and miss fewer weeks.
If you're already dealing with pain from a ramp-up, or you want to build your load properly from day one, the Running Assessment at PRT is built for this. We look at how you move, where your volume has been, and what you're training for, and we build a plan around it.