On November 8, 2025, on the Tunnel Hill course in Vienna, Illinois, USA, the women's ultra-distance world records for 50 miles and 100 miles were rewritten on the same day.
Anne Flower, an emergency physician from Colorado, USA, set a new women's world record at the Tunnel Hill 50-mile race (approximately 770 m total elevation gain) with a time of 5 hours 18 minutes 57 seconds.
This broke the 5:31:56 course record set last year at the same venue by Courtney Olsen.
On the 80.47 km course, Flower held an average pace of 3 minutes 57 seconds per kilometer. Even after temperatures rose around midday, her rhythm remained steady with no significant fluctuation.
The former marathoner switched to trail running in 2019 and competed in the 2020 U.S. Olympic marathon trials. Since moving into ultra distances, her results have steadily improved.
She won the Javelina 100K in fall 2024 and the Silver Rush 50-mile in 2025.
This summer Flower attempted 100 miles for the first time and broke Anne Threlfall's 31-year course record at the high-altitude Leadville 100 (average elevation above 3,000 m), which helped build her confidence for this flat ultra performance.
Flower is an emergency physician who works long and intensive shifts. In an interview with iRunFar, she said she often trains between shifts and sometimes goes for long runs right after night duty. In that interview she described running as “a way to reset outside of clinical work.”
On the same day, in the Tunnel Hill 100-mile race (about 1,035 m elevation gain), Ireland’s Caitriona Jennings set a new women's 100-mile world record in her first attempt at the distance with a time of 12 hours 37 minutes 04 seconds.
Jennings averaged roughly 4 minutes 42 seconds per kilometer during the race,and for the first 80 miles she kept nearly every mile at about 7 minutes 26 seconds, with variations of less than two seconds, only slowing slightly in the final stages.
Although this was her first 100-mile attempt, Jennings is a highly experienced ultra runner. She began as a marathoner and represented Ireland in the marathon at the 2012 London Olympics.
Now 43, Jennings is in her prime as an ultra runner. In February 2025 she set the Irish 50K record at Donadea with 3:16:33 and currently holds Ireland’s 100K record (7:43:01).
The fact that two records fell on the same day at the same venue makes you wonder: what kind of course is this?
The Tunnel Hill course is a converted rail-trail made of crushed stone. It’s relatively flat (around a 2% grade) with a stable surface, and runners start in the town of Vienna and run out-and-back — the 50-mile field does one loop, the 100-mile field does two.
This course is widely regarded in the international ultra community as a fast course.In 2017 Camille Herron set the women's 100-mile world record here; in 2023 Charlie Lawrence set the men's 50-mile record (4:48:21); Courtney Olsen’s 5:31:56 in 2024 broke the women's 50-mile mark (pending certification).In 2025 the course witnessed the women’s records by Flower and Jennings (pending certification).
Tunnel Hill races are USATF-certified and hold IAU Gold Label status. This year's 50-mile event also served as the USATF national championship.
Under IAU rules, these two women's ultra-distance records still require formal ratification by the IAU. We await official confirmation.
