If anything has characterized the 2018 track season thus far, it’s been the changing of the guard we’ve seen in many events, particularly in the sprints.

The aging Justin Gatlin and retired Usain Bolt have handed the torch to youngsters Christian Coleman and Noah Lyles in the short sprints. The name Allyson Felix is nowhere to be found at the top of the yearly marks, having been replaced by the likes of NCAA stars Lynna Irby and Kendall Ellis. And Sydney McLaughlin and Michael Norman have catapulted themselves into superstar territory in track and field circles.

We’ve seen less of this trend in the longer distance races, but could there be a shift in the power structure coming soon in the women’s middle distances?

Without a doubt, Jenny Simpson has been the alpha dog of U.S. 1500 meter running in recent years. She’s won the last four 1500m outdoor national titles and has four global medals over the metric mile distance, including a thrilling silver medal at last summer’s World Championships.

https://www.youtube.com/watch?v=5hu-Rvks0SU

Despite her dominance, she showed a bit of vulnerability a few weeks ago at the Pre Classic, when fellow American Shelby Houlihan unleashed a furious kick on the final straightaway to pull off the upset in a personal best 3:59.06, besting her personal best by over four seconds.

The race was Houlihan’s first career victory against Simpson.

We have all witnessed Houlihan’s big kicks in the past (see her dominant U.S. indoor doubles the last two years) but never before had she exhibited that kind of closing speed on a stage as big as a Diamond League meet.

Houlihan’s progression makes you wonder if she might be prepared to take the U.S. women’s 1500m championship belt from Simpson in the near future.

If father time is indeed undefeated, that day may be coming sooner than later, as Simpson turns 32 years old this August, while Houlihan is just 25 years of age.

All of this makes the matchup between Simpson and Houlihan this weekend at the USA Outdoor Championships in Des Moines all the more fascinating, as both athletes return to a state where they have roots (Houlihan was a dominant runner on the Iowa prep scene, while Simpson spent part of her early childhood in the Hawkeye State) to race on the Blue Oval.

Editor’s note: Both have declared for the 1500 meters, though Houlihan is also entered in the 5000 meters. It’s a doable double, though it certainly isn’t easy — the 1500m prelims are on Thursday, 1500m final is on Saturday and 5000m final is on Sunday.

We know, of course, that winning in a fast, rabbited race like Houlihan did at Pre isn’t the same as doing so in tactical championships contests, which Simpson has mastered in her career.

With a gun to my head, I still pick the more experienced Simpson in the confines of this weekend’s championship meet, but don’t be surprised if Houlihan continues inching toward earning the title of America’s best miler.