The longer the distance run, the more women have an edge over their male competitors. Yet, the longer the distance, the less likely women are to start the race. In this incredible and personal account, established running journalist Jen Benson looks at the science, hidden history, and what it takes to run an ultramarathon - unveiling why women are so well adapted for endurance sports. Detailing her own account of completing her first 100-mile ultramarathon, Jen brings to the fore the harshness, humour, and personal sacrifice of ultra-running. Interweaved with this are unprecedented interviews with some of the greatest ultra-women of the past 40 years, including Jasmin Paris, who triumphed in a 268-mile winter Spine Race despite stopping to express milk for her baby, and Eleanor Adams, the first woman to complete a 153-mile Spartathon ultramarathon despite opposition from male organisers. A testament to the feats of women that challenge the very limits of human capability, this is the remarkable sporting history of extreme performance hitherto untold.