Sexism.
Via The Times UK:
Women have more stamina than men and do better at endurance events, according to scientists.
Although men are bigger and more powerful, women outlast them in the most gruelling tasks. A man’s strength decreased 15 per cent more than a woman’s after repeating an exercise 200 times, researchers at the University of British Columbia, Canada, found.
It adds to a growing body of evidence that women are better at endurance events. Scientists have suggested that they will soon be regularly beating men in marathons.