The ultimate limit of human endurance has been worked out by scientists analysing a 3,000 mile run, the Tour de France and other elite events.

They showed the cap was 2.5 times the body’s resting metabolic rate, or 4,000 calories a day for an average person.

Anything higher than that was not sustainable in the long term.

The research, by Duke University, also showed pregnant women were endurance specialists, living at nearly the limit of what the human body can cope with.