At every mile marker of the 2019 Chicago Marathon, Jimmy Choi dropped to the ground for a burpee—complete with push-up—and then jumped back up on his feet before he got back to running. For each mile marker on the course, he did that same number of burpees—from one on the first mile to 10 on the 10th, all the way up to 26 on the 26th mile—adding another hard effort to the already grueling marathon distance. By the time Choi, 43, reached the finish line in 5:56:03, he had completed a total of 351 burpees in addition to running 26.2...