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 the Rule Says
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 Your Legs Lie to You
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 Shows Up When You Ignore It
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 to Actually Use It
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.
The Cutback Week
Every 3 to 4 weeks, drop your mileage by 20 to 30%. You're not resting. You're giving your tendons and bones a window to catch up to the stress you've been piling on.
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 the Rule Misses
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.