Trail and ultra running super star Courtney Dauwalter is in hospital with severe bronchitis. She was over 350km into an attempt to set the fastest known time (FKT) on the 788km Colorado Trail when she began to wheeze.

“We made the call to take her to the ER in Leadville. Her [oxygen saturation was] 70 so the doctors here ran a full range of tests for HAPE [high altitude pulmonary edema], blood clots, and other severe conditions. Thankfully those were all ruled out and they determined she has acute bronchitis,” her team posted on Instagram.

Dauwalter is one of the best trail runners in the world. She has claimed podiums in everything from 50km races to the high profile 170km Ultra Trail du Mont Blanc. Her fame transcended the sport when she won the Moab 240 (386km) outright, beating the next closest competitor by over 10 hours.

On Thursday, Dauwalter set off on her latest challenge – the Colorado Challenge FKT, from Waterton Canyon to Durango. The record is eight days, 30 minutes, set by Bryan Williams.

“This definitely wasn't in the plan,” Dauwalter’s post read.

“It could have been allergy induced, or from all the dust/dry heat, plus an impaired immune system from her run. She's on oxygen until her levels come back up, but she should be perfectly healthy in a few days. We’re crushed it had to end this way, but ever grateful she’s on the mend.

“We would like to extend a heartfelt thank you to everyone who followed along during Court’s CT attempt. Your cheers and kind words mean the world to us! Be well everyone,” the post added.