The three parts
The triad describes three connected problems seen in female athletes. Not eating enough for training and growth comes first. Periods becoming irregular or stopping follows. Bone that is weaker than it should be, at the very age it should be strengthening, follows from that.
You may also hear about RED-S, a broader idea that covers the same energy shortfall in both sexes and includes effects on immunity, mood, gut and performance. The triad remains a useful shorthand for the female pattern because the three parts point at each other so reliably.
1
Energy shortfall
Training or growth rises, food does not, often for months without anyone noticing.
2
Cycle changes
Periods become lighter, gappier, or stop. Frequently dismissed as normal for sport.
3
Bone affected
Bone building slows during the key years, raising the risk of bone stress injuries.
How the triad usually develops
Who it affects
It is more common in endurance sport, gymnastics, dance and any activity where leanness is emphasised, but it turns up in team sport too. Importantly, an athlete does not have to look underweight to be under-fuelled, and often does not.
In most cases there is no eating disorder, just a busy schedule and a growing body. Where restriction is deliberate, specialist support is needed as well.
Warning signs across the three parts
- Fuel: skipped meals, long gaps on training days, no weight gain through a growth spurt, cutting out food groups.
- Cycle: periods late to start, becoming irregular, or stopping for three months.
- Bone: a stress fracture, a second bone injury, or shin or foot pain that keeps returning.
- Across all three: constant tiredness, frequent illness, low mood, performance sliding despite training.
What happens at the GP
Expect questions about training hours, eating, periods and injuries, plus blood tests that typically include iron, thyroid and hormone levels. Where there have been bone stress injuries or a long absence of periods, a bone density scan may be arranged, and a referral to a sports dietitian is often the most useful part.
Take a written summary: training hours per week, growth over the last year, dates of periods, and any injuries. It makes a ten-minute appointment count.
What treatment looks like
Addressed early, this usually resolves with straightforward changes. Left for a year or two, the bone consequences are much harder to undo.
- More energy in, especially around training, as the first and biggest change.
- A review of weekly load, often reducing volume rather than stopping sport.
- Calcium and vitamin D checked and corrected.
- Iron checked and treated if low.
- Strength and impact training kept in, because loading builds bone.
- Ongoing review, since cycles and bone respond over months, not weeks.