An athlete came to me with a third stress reaction in eighteen months. She had done the rehab properly every time, she had built back carefully, and it kept happening.
We went through her training and it was reasonable. Then we went through what she ate, and it took about four minutes to find the answer.
She was training fifteen hours a week on roughly what a sedentary person eats. Not deliberately, not with any disordered intent. She simply had no idea how much fifteen hours actually costs.
You cannot build tissue out of nothing, and no amount of good rehab will substitute for the material.
What Energy Availability Means
Take what you eat, subtract what your training burns, and what remains is what your body has left to run everything else. Bone remodelling, hormone production, immune function, tissue repair, your brain.
When that remainder drops too low for long enough, your body starts making cuts. Not because anything is broken, but because it is doing sensible triage with insufficient resources.
The cuts tend to land in the same places. Reproductive hormones go first, because reproduction is expendable in a shortage. Bone formation slows. Thyroid output drops, metabolic rate falls. Immune function declines. Mood and sleep degrade.
The condition has a name now, Relative Energy Deficiency in Sport, and the important part of that name is relative. This is not about being underweight. Plenty of athletes with entirely normal body composition are in it, which is exactly why it gets missed.
Why It Goes Unrecognised
Because every symptom individually has a more comfortable explanation.
Tired all the time is overtraining. Poor sleep is stress. Getting every cold going round is bad luck. Recovery taking longer is age. Low mood is winter. Stress fractures are ramping too fast. Loss of periods is treated by a distressing number of female athletes, and occasionally by their coaches, as a normal consequence of being fit rather than as the clearest single warning sign there is.
Each one is explainable. It is only the pattern that gives it away, and nobody sees the pattern because each symptom gets discussed with a different person on a different day.
The Signs I Watch For
Recurrent bone stress injuries, especially more than one in a couple of years, in an athlete whose training progression looks sensible. That is the one that brought her to me and it is the loudest signal on the list.
Any disruption or loss of the menstrual cycle. This is not a normal adaptation to training. It is a hormonal consequence of insufficient energy and it comes with a real cost to bone that accumulates quietly for years.
In men, reduced libido and persistently flat mood, which is the same hormonal story with less obvious signalling.
Getting ill repeatedly. Feeling cold constantly. Poor sleep despite fatigue. Performance that has plateaued or declined across a block where training went well. And a slow drift downward in resting heart rate combined with a drift downward in performance, which is not the good kind of low resting heart rate.
What I Actually Do
I am a coach, so I want to be clear about the boundary before anything else. If several of the above are present, particularly a lost cycle or repeated bone injuries, that is a medical conversation and a registered sports dietitian's conversation. Not mine, and not something to work out from an article.
What I can do is the arithmetic and the practical part, and the practical part is usually where it is going wrong.
Most athletes I find in this state are not restricting on purpose. They are under-fuelling by accident, and it is nearly always the same accident: not eating around training. They train fasted in the morning, eat a normal lunch four hours later, do a second session in the evening, and have dinner. The total might not even be terrible. The timing means they spend the majority of the day in a deficit their body has to manage.
So the first intervention is almost always carbohydrate before, during and immediately after sessions, rather than a change in total intake. Fixing when the food arrives resolves a surprising proportion of cases.
The Part That Is Hard to Say
Endurance sport has a weight problem, and it is dressed up as professionalism.
Athletes are surrounded by the idea that lighter is faster, and over a narrow range it is. What does not get said is that the athlete who gets light by under-fuelling gets faster for one season and then spends the next two injured, and that the performance gain was borrowed rather than earned.
I have coached people through that arc and it is not a good trade. The athletes who last are not the lightest ones.
The Bottom Line
If you have had more than one bone stress injury, or you have lost your cycle, or you are permanently cold and ill and tired despite training going well, do not accept a separate explanation for each of those things.
Look at whether you are eating enough for the training you are doing, and start with what you eat around sessions rather than with the daily total. Then go and talk to a doctor and a sports dietitian, because this one is genuinely outside what a coach should be handling alone.
