Dean Karnazes has pushed his body and mind to inconceivable limits, from running in the shoe-melting heat of Death Valley to the lung-freezing cold of the South Pole.

He's raced and competed across the globe and once ran 50 marathons, in 50 states, in 50 consecutive days. In A Runner's High, Karnazes chronicles his return to the Western States 100-Mile Endurance Run in his mid-fifties after first completing the race decades ago.

The Western States, infamous for its rugged terrain and extreme temperatures, becomes the most demanding competition of his life, a physical and emotional reckoning and a battle to stay true to one's purpose.

Confronting his age, wearying body, career path and life choices, we see Karnazes as we never have before, raw and exposed.

A Runner's High is both an endorphin-fuelled page-turner and a love letter to the sport from one of its most celebrated ambassadors.