Earlier this week at Icahn Stadium, two hours before NYRR’s Tuesday at the Races, Stuart Calderwood ran 400m on the track and saw the lap-counter read 74 laps — 29.6 km — to go. A daunting number, particularly in uncomfortable humidity that made it challenging to run consistent splits. In any case, Stuart, along with a small team of pacers, ran a brisk opening 10k at about six-minute pace. Two pacers dropped out. Stuart and his two remaining pacers, Steven Monte and Tommy Dichiara, kept knocking off laps as people started to trickle in to register for Tuesday night’s meet. By the time Stuart ran his 75th lap solo, he’d set the American 50-54 age-group record for 20k (1:17:42), 25k (1:38:51), and 30k (2:00:31).