In this lecture, Andy Jones will discuss the scientific background to, and legacy of, his involvement in Nike’s  ‘Breaking 2’ (men’s marathon) and ‘Breaking 4’ (women’s mile) projects. Specifically, he will break down the physiological requirements of these immense challenges, the physical characteristics of the athletes capable of tackling them, and the other factors that need to be taken into account to enable these athletes to fully express their physiological potential. These factors include the environment, footwear innovation, nutrition, pacing and drafting. Lessons learnt from participation in these challenges will be considered with a view to predicting what the ultimate limits to human athletic performance might be.