Every summer it's the same story. The race calendar fills up, the mileage creeps north, and a few weeks later half my feed is in a moon boot with a rueful caption. Stress fractures have quietly become one of the most common ways a good season comes undone, and the runners they're happening to aren't unlucky. They're usually doing one or two ordinary things, and stacking them.

This is a plain piece on why stress fractures are rising, what's actually causing them, and how to keep building toward a strong season without joining the list.

Why bone breaks down before it builds up

Bone is living tissue. Every time you run, you create tiny amounts of damage to the structural cells inside your shins, feet, and hips. In the days after a hard session, your body sends in resources to rebuild that bone, and to lay it down slightly stronger than it was. That's how training works at the skeletal level: stress, then repair, then a tiny upgrade.

The catch is that the rebuild runs on a slower clock than your enthusiasm does. Soft tissue (muscles, tendons) recovers in a couple of days. Bone needs longer, sometimes a week or more depending on the load. If you add miles, hills, and harder sessions all in the same fortnight, the damage starts outpacing the rebuild. That gap, widened week after week, is where a stress fracture lives. The bone keeps absorbing damage faster than it can patch itself.

This is why a runner can train hard for years and then crack a metatarsal not in the deepest block of a plan, but in the third or fourth week of a sudden ramp. It isn't strength that gave way. It's timing.

The second cause, sitting quietly underneath

Load is one half of it. Fuel is the other.

I used to think stress fractures were just unlucky. A single misstep, a freak collision of pace and surface, a body folding for no obvious reason. What I learnt watching enough runners go through one is that they almost always come with a second ingredient: not enough food for the work being done.

When you're under-fuelled, your body triages, and bone-building is one of the first things it quietly turns down. This is the same dynamic I wrote about in "Why you're always cold (even in a heatwave)", because cold hands are one of the body's first signals that something has been down-regulated. Under-fuelling lowers thermogenesis, dampens cycle function, and at the skeletal level, it reduces the bone formation that should be keeping pace with the load you're putting through.

Low energy availability and a fast training ramp are a genuinely risky combination. Either one alone is manageable. Together, they're how a lot of runners, particularly women runners, end up in the boot. Bone keeps score whether you're paying attention or not.

The warning signs worth stopping for

Stress fractures rarely arrive without notice. They tend to whisper for a week or two before they shout. The trick is recognising the whisper.

The signals worth stopping for:

  • A pinpoint ache you can press on with one finger, not a vague all-over soreness.
  • Pain that gets worse as a run goes on, instead of warming out of it.
  • Pain that lingers after you've stopped, sometimes into the evening or night.
  • Tenderness over a specific spot on the shin, foot, or hip.
  • Pain when you hop on the affected leg, or when you press the bone firmly.

One of those in isolation, on a body that's been training sensibly? Probably fine, and probably worth a few easy days. That cluster, in someone who's just ramped up fast or who's been under-fuelling? Stop running and get it looked at. Caught early, a stress reaction is rest and patience. Run through it, and it can become weeks in a boot, plus a complicated rebuild.

The mindset move here is unglamorous and important. Tough runners don't run through aches that are trying to tell them something. The smart ones know which aches to stop for.

How to keep building without becoming a cautionary tale

The good news is that stress fractures are largely preventable. The principles are simple. They just get routinely ignored when a race date starts looming.

Ramp gradually

Add load in small steps, and take a lighter week roughly every fourth one. Your bones do most of their adaptation on the down week, not on the hard ones. A useful rule: don't increase volume or intensity by more than around 10% from one week to the next, and never both in the same week.

Change one thing at a time

More miles, or faster, or more hills. Not all three in the same week. Pick one variable to push, hold the others steady, and see how your body responds before you stack another change on top.

Fuel the build

A bigger training load needs more food, not the same amount. Carbs and protein, consistently. If the volume is going up and your appetite is climbing, that's information. Feed it.

Keep the strength work in

Loaded, controlled strength training (squats, lunges, single-leg work, calf raises) builds bone too, and it's usually the first thing that gets dropped when running takes over. Two short sessions a week is enough to protect against the worst of the bone-stress risk.

Respect pinpoint pain

Bone pain you can locate with a fingertip is a stop sign, not a warm-up problem. If pressing one spot reproduces it, the run can wait. The conversation with a doctor can't.

When to get help

If you've taken a few easy days, given an ache time to settle, and it's still there or getting worse, see your GP or a sports doctor. Ask about imaging if your symptoms fit the cluster above. Stress fractures often don't show on an X-ray in the early days but will on MRI, and catching one at the stress-reaction stage rather than the full-fracture stage is the difference between two weeks off and twelve.

If your periods have stopped, you've been losing weight without trying, or you recognise yourself in the under-fuelling pattern, mention that too. Stress fractures sit in the family of symptoms that come with RED-S, and a doctor who's looking at the whole picture will help you a lot more than one who treats the cracked bone in isolation.

Build slowly, fuel the work, and stop for the aches that are trying to tell you something. That's the whole game. Run patient. Stay off the feed.

This article is general information, not medical advice. If you suspect a stress fracture, or if you've noticed changes to your periods alongside training, please speak to your GP or a sports doctor.