Most running niggles don't come from running. They come from running more, faster than your body can keep up with. Here's how to build mileage so the fitness and the tissues grow together.
01Why big jumps cause trouble
Your heart and lungs adapt to training quickly. Tendons, bones and the tissue around your joints adapt much more slowly. That gap is the danger zone: after a few good weeks you feel ready for more, but your Achilles, shins and knees haven't caught up yet.
So the aim isn't to avoid hard training. It's to raise the load gradually enough that everything adapts at roughly the same pace.
02The 10% rule (and its limits)
The classic advice is not to increase your weekly mileage by more than 10% at a time. It's a useful guardrail, especially if you're newer to running, but it isn't a law. Ten percent of 10 miles is a single mile, while ten percent of 60 is a whole extra run.
Recent research suggests the weekly total may matter less than many runners assume, which brings us to the bigger point.
03Watch your longest run, not just your week
A large 2025 study in the British Journal of Sports Medicine followed 5,205 runners wearing GPS watches for 18 months. The researchers found that week-to-week changes in mileage showed no clear link to injury. What did matter was how long each single run was compared with the longest run in the previous 30 days.
| Single run vs your longest in the last 30 days | Injury rate vs keeping it within 10% |
|---|---|
| Up to 10% longer | Reference |
| 10% to 30% longer | About 64% higher |
| 30% to 100% longer | About 52% higher |
| More than double | About 2.3 times higher |
Know your longest run from the last month. Keep any new run within about 10% of it. If your longest recent run is 10 miles, your next long run should be about 11 miles at most, not 13.
04Build in cutback weeks
Every third or fourth week, drop your mileage by roughly 20 to 30%. Keep a little quality in the week but take the volume down. Cutback weeks are where adaptation catches up, and they often make the next build week feel easier.
A simple pattern is three weeks up, one week down. Older runners, or anyone coming back from a layoff, may do better with two up, one down.
05Change one thing at a time
More miles, faster sessions, new hills, new shoes, a switch from road to trail: each one is a new load. Stack three in the same fortnight and you've made a big jump without realising it. Add one thing, let it settle for a couple of weeks, then add the next.
06Keep most of your miles easy
When mileage goes up, most of the extra should be at a genuinely easy, conversational pace. If you can't speak in full sentences, it isn't easy. Plenty of runners build volume while also running everything at a moderate effort, and that's when fatigue piles up.
A useful rule of thumb is that roughly 80% of your weekly running should feel easy.
07Strength work is injury insurance
Two short strength sessions a week help your legs cope with the repetitive load of running. Focus on:
- Calf raises, straight and bent knee, building up to single-leg and weighted. Your calves and Achilles take a huge share of the load on every stride.
- Split squats or single-leg squats for knee and hip control.
- Hip bridges and side planks for the hips and trunk.
- Step-downs from a low box, slow and controlled.
Twenty to thirty minutes is enough. Consistency beats intensity here too.
08Sleep and fuel the build
Adaptation happens between runs. Two things matter most:
- Sleep. A big week on short sleep is a big risk. Protect your sleep in the heaviest weeks of the block.
- Eat enough. More miles means more energy needed. Under-fuelling during a build is a common and underrated cause of problems. Include protein at every meal and plenty of fruit and veg.
09Soreness or pain? Know the difference
General muscle soreness after a harder week is normal. Pain that's sharp, localised to one spot, gets worse as you run or makes you change how you run is not.
Many physios use a simple traffic-light check. Rate any discomfort out of 10 during and after a run:
- 0 to 3, settled by the next morning: generally fine to carry on.
- 4 to 5, or still there the next morning: back off. Shorten runs, cut the intensity, add a rest day.
- Above 5, or getting worse: stop running on it and get it checked.
If a niggle hasn't settled after a few days of reduced training, if there's swelling, or if you've got pain at night or at rest, see a physio or your GP. Bone pain in the shin or foot that's tender to touch in one small spot needs checking quickly.
10An example 12-week half marathon block
Here's how the principles above look in a real block for a runner starting at around 15 miles a week. Treat it as a shape to follow, not a prescription.
| Week | Miles | Longest run | Notes |
|---|---|---|---|
| 1 | 15 | 6 | Settle in, all easy |
| 2 | 18 | 6.5 | Add a few strides after one run |
| 3 | 21 | 7 | First steady session |
| 4 | 16 | 6 | Cutback |
| 5 | 23 | 7.5 | Back to building |
| 6 | 26 | 8 | One tempo session |
| 7 | 29 | 8.5 | Longest run creeps up |
| 8 | 22 | 7 | Cutback |
| 9 | 31 | 9 | Peak phase starts |
| 10 | 34 | 9.5 | Biggest week |
| 11 | 24 | 8 | Taper |
| 12 | 19 | 13.1 | Race week |
Notice the longest run never grows by more than about 10% on the longest of the previous month. Race day is the exception: by then you're tapered, rested and the adrenaline is on your side.
Same routine, every week of the block.
Mileproof is a daily collagen and vitamin C formula for runners. Vitamin C contributes to normal collagen formation for the normal function of cartilage.
Source: Frandsen JSB, Hulme A, Parner ET, et al. How much running is too much? Identifying high-risk running sessions in a 5200-person cohort study. British Journal of Sports Medicine 2025;59:1203–1210. This guide is general information, not medical advice.