Why Usain Bolt wouldn't run a marathon
How sprint performance suffers from intensive endurance training, the molecular mechanism behind it, and what to do if you need both.
In 1980, researcher and weightlifter Hickson found that adding endurance training to his programme caused his strength to decline. He called this the interference effect. The molecular mechanism is direct: strength adaptations rely on the mTOR pathway; endurance adaptations activate AMPK; AMPK inhibits mTOR. High-intensity endurance work above roughly 70% of maximum heart rate generates enough AMPK activity to actively suppress the hypertrophy signal from the gym session that followed.
The article covers the molecular basis of the interference effect, what makes it worse (running creates more interference than cycling; intensity matters more than volume), and practical strategies for athletes who need both strength and endurance: managing session timing, intensity ceilings, exercise modality, and nutrition. Published on Medium, August 2022.