The basic equation
Bone gets stronger when it is loaded and then given what it needs to rebuild. Bone stress injuries happen when the loading goes up faster than the rebuilding can follow, or when something is limiting the rebuilding.
That is why two athletes can run the same mileage with completely different outcomes.
Load-side risk factors
- A sudden jump in training, new season, new squad, a training camp.
- Multiple teams, school and club, with nobody adding up the total.
- High repetitive impact volume, distance running, tumbling, repeated jumping.
- Little or no strength training alongside the running.
- Training on very hard surfaces, or a big change of surface or footwear.
Athlete-side risk factors
- Not eating enough for training and growth.
- Periods absent, stopped, or late to start.
- Low vitamin D, common in the UK in winter.
- Low calcium intake, often from dropping dairy without replacing it.
- Low iron and persistent fatigue.
- A previous bone stress injury, the strongest signal of all.
- Rapid growth, when bone is temporarily less able to cope.
Lower risk
- Load rises gradually
- Two strength sessions weekly, all year
- Eats before and after training
- Regular periods
- Vitamin D in winter
Higher risk
- Big jump in September
- Running only, no strength work
- Long gaps between meals
- Periods stopped months ago
- Previous stress fracture
Two athletes, same sport
What to do about it
- Add up the real weekly total across every team and activity.
- Increase load in steps, and hold it steady during a growth spurt.
- Two strength sessions a week including jumping, all year round.
- Eat around every session, and increase food when training increases.
- Vitamin D supplement through autumn and winter.
- Treat any missing period as something to check, not to ignore.
Catching it early
Ask about bone pain, not just soreness. Pain in one small spot, tender to press, that comes on earlier in each session is the pattern that matters. Caught at that point the interruption is usually weeks; ignored, it becomes months.