From a recent interview with Runner's World (today's Quote of the Day):
SH: He came up to me after a workout I did a few weeks ago and said, “You 100 percent can get the American record. Whether or not it will happen, we don’t know, but I know you can do this.” I needed that verbal confirmation and he knows that. He knows I need that feedback because I don’t know how to tell based on the workouts. Most of the time I’m going off what Jerry’s saying.
RW: What was that workout that tipped you and Jerry off?
SH: It was three sets of 1200 meters with three minutes rest, 400 meters with one minute rest, 400, then three minutes rest between the sets. And he wanted me to run race pace, which is 71 [seconds per 400 meters] for the first 1200, 70s for the second 1200, then 69s for the third 1200. I was 69.70 for the first one, 69 for the second, then 69 down to 67 for the last one. My 400s were supposed to be 68 [seconds] but I was running 66s or 65s. It was feeling super controlled and very easy. It was coming naturally—it was the pace my body wanted to run.
After that workout he was like, “Yeah. You’re ready to do this.”
Our article on the race: http://www.letsrun.com/news/2018/07/shelby-houlihan-runs-1434-45-break-american-5000m-record-heusden/