Training fatigue is normal. Overtraining is not. And very often, what runners call “overtraining” is actually a mix of excessive load, poor recovery, and under-fuelling.

This episode explains the difference between normal fatigue, non-functional overreaching, true overtraining syndrome, and Relative Energy Deficiency in Sport, or RED-S. The key message is that not all fatigue is the same, and the solution depends on the cause.

For ultrarunners, the biggest risks often come from stacking hard training, life stress, poor sleep, and low energy availability for too long. Warning signs include persistent tiredness, loss of performance, poor recovery, low mood, repeated illness, hormonal disruption, and recurring injuries.

The practical takeaway is simple: monitor warning signs early, fuel properly for the work you are doing, and make recovery as deliberate as training. The goal is not to avoid fatigue, but to make sure it is recoverable.

Main takeaway: Your body does not adapt to training you survive. It adapts to training you can recover from.

Key references

• Meeusen et al. ECSS-ACSM consensus on overtraining syndrome.
• Mountjoy et al. 2023 IOC consensus statement on RED-S.
• Stellingwerff et al. Overtraining Syndrome and RED-S: shared pathways, symptoms and complexities.
• Saw et al. Subjective self-reported measures for monitoring athlete fatigue.
• IOC consensus on load in sport and risk of injury.