New research shows that an extreme protocol – 10 HIIT sessions in 7 days – can put the body into shutdown mode: reduced hemoglobin, fewer red blood cells, increased creatine kinase (muscle damage) and signs of impaired immune function.
HIIT is a powerful tool for boosting fitness. But overdose it, and your body responds by lowering its capacity. A period of extreme intensity without recovery risks becoming a setback for both performance and health.
A new study published in Cell shows that 10 HIIT sessions in 7 days wrecks recovery:
- Hemoglobin down
- Red blood cells down
- Creatine kinase (a marker of muscle damage) up
- Immune function impaired
In short: the body goes into shutdown mode.
Conclusion: The body does not respond in a linear way – more is not always better, especially at high intensity.

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