Stamina’s what’s interesting in bipedal human beings—how long we can keep it up. Horses rapidly tire at their top speeds, lathering and needing to stop after only a couple of miles. Given enough time, a human could actually run a horse down. Most healthy human adults can trot at, say, five miles an hour, for hours at a time. Ultramarathoners can pretty much go for days if they get sleep breaks. Horses? They’d die.
