Even purely recreational runners can come to know what racers know: that the most enjoyable times in running come when you are teetering on the edge of fatigue but hang on a moment longer, and a moment longer, and at some point discover not only that you can bear it but that you can even pick it up a bit. That is the greatest thrill in endurance athletics – a greater thrill, even, than winning. And it is available to the totally non-competitive runner, so long as you're willing to avail yourself to the opportunity – the freedom – to experiment with levels of fatigue.