He talks of wanting to become the world's best endurance runner, not boastfully but with a thrilling sense of discovery.

In endurance runners, low body weight can lead to irregular periods.

Extreme endurance runners have been pounding the world's wild places for a few decades now, rail-thin and hurting in ways too intense to put into words.

Because they bound in long flat jumps and have not been observed to run, they are not thought to be endurance runners.

Approximately one third of endurance runners experience transient but exercise limiting symptoms, and repetitive gastrointestinal bleeding occasionally causes iron deficiency and anaemia.