What's behind it
The technical term is relative energy deficiency in sport, RED-S for short. It describes a state in which, over a longer period, less energy is available than training and basic metabolism need together. It doesn't have to come from a deliberate diet – it often simply happens because training volume goes up and eating doesn't keep pace.
If energy is lacking for a long time, the body shuts down what isn't essential for survival at the moment. The cycle is one of the first functions to stop. The International Society of Sports Nutrition's position stand on female athletes' nutrition deals with exactly this link and puts sufficient energy availability first.
How you can recognise it
- Your period stops or becomes much more irregular
- Ongoing tiredness; performance drops although you train more
- Infections become more frequent, injuries and wounds heal more slowly
- Shin or bone pain without a clear cause
- Sleep gets worse, mood drops, you feel the cold more
None of these signs proves anything on its own. Several together, over weeks, are a reason to look more closely.
Why the misconception is so persistent
In an environment that rewards discipline, a missing period looks like proof that you mean business. On top of that, symptoms are absent at first: performance often holds up for a while before it collapses. That's exactly why the point at which a correction would have been easy gets missed.
In the long run, more is at stake than the cycle. Bone density, the immune system and the adaptation to training itself are affected – exactly what you are training for.
What we do differently in the app
Rhythmus asks about your energy level every day and suggests a gentler session when it's low, instead of pushing the plan through. Your calorie needs are calculated from your details and not artificially scaled down: the app has no weight-loss promise and no preset deficit. And if your period stops, it doesn't quietly disappear from the statistics – it is visibly missing from the calendar.