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Overtraining Syndrome: How to Spot the Warning Signs (HRV, Heart Rate, Mood)

Updated: August 1, 2026

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Pushing your limits is part of sport, but when fatigue no longer fades despite rest, it may be overtraining syndrome (OTS). A case study published in July 2025 in BMJ Case Reports, on three endurance athletes, and a systematic review published in May 2025 in Physiological Reports on heart rate variability (HRV), help clarify which physiological and psychological signals deserve attention — and how to act before the situation worsens.

A continuum, not a switch

The reference framework remains the joint ECSS/ACSM consensus of 2013, still widely cited in recent literature. It distinguishes three stages on the same training-stress continuum:

Functional overreaching: intentional, short-lived performance drop, recovery within a few days.
Non-functional overreaching: more marked performance drop, accompanied by neuro-endocrine and/or psychological signs, recovery over several weeks to a few months.
Overtraining syndrome (OTS): severe form of non-functional overreaching, with prolonged performance drop, persistent fatigue, and symptoms that can last months.

The early warning signals to watch

Heart rate variability (HRV): the 2025 review shows a decline in HRV can precede the performance drop. A downward trend over several days, especially if it persists after a rest day, is worth taking seriously.
Resting heart rate: a morning resting heart rate noticeably higher than your usual baseline can signal incomplete recovery.
Mood and motivation: irritability, loss of enthusiasm, poor sleep quality and low perceived recovery are often the first signs athletes notice.
Performance: a drop in times, weights, or training paces that persists despite adequate rest.

How to act

Reduce training volume or intensity for several days to a week and monitor whether HRV and mood recover.
Prioritize sleep (9+ hours for athletes), adequate protein and calories, and stress management.
If symptoms persist for more than 2–3 weeks despite reduced training, consult a sports physician — OTS can require a longer recovery plan and may involve hormonal or psychological follow-up.

This article summarizes general scientific findings for educational purposes and is not a substitute for individualized medical advice.