Distance running is a sport where the line between productive hard training and training that is breaking something is genuinely difficult to see from the outside. The physical adaptation and the physical breakdown look similar for a while, and the athlete often cannot tell the difference either.
The performance signal is the clearest one. A runner who is training consistently and working hard but whose race times are getting slower or flat across six weeks is not in a productive training phase. Performance should trend up with consistent training over a season. When it does not, the load or the recovery is wrong, and more training will make it worse, not better.
Injury pattern is the second signal. One injury in a season is part of distance running. Recurring minor problems in the same area, shin pain that keeps coming back, IT band tightness that never fully resolves, metatarsal soreness that flares with every race, is a pattern. Runners who have a chronic low-level issue that their body is managing rather than healing are at elevated risk for a stress fracture. Stress fractures in the shin, foot, and femur are the severe end of a continuum that starts with these recurring warnings.
Mood and motivation changes are real signs that get dismissed too easily. A runner who used to love the daily run and now has to be pushed out the door every day, who is more irritable or emotionally flat, who has lost the competitive interest they had six months ago, is telling you something. That pattern, alongside physical fatigue, is consistent with overreaching and in its more serious form with overtraining syndrome.
In female runners, the relative energy deficiency in sport (RED-S) pattern is a specific and serious risk. It involves inadequate caloric intake relative to training load, which disrupts hormonal function and bone density. Irregular or absent periods in a teenage girl who is training heavily is a clinical sign, not a normal training adaptation. It requires a pediatrician or sports medicine physician to evaluate, not a wait-and-see approach.
The right response when these signs appear: a rest week, a conversation with the coach, and a pediatrician visit if the pattern has been present for more than two or three weeks. Pushing through this pattern to stay on the training schedule produces worse outcomes, not better