On Saturday, Dave Mackey, 46, tweeted that he was heading to his “office” at 8,500 feet, joking that it was a “tough job. Someone’s gotta do it.”

Not long after, the decorated ultrarunner who once held the fastest known time for the double crossing of the Grand Canyon, slipped and fell on his way to the Summit of Bear Peak, close to Boulder, Colorado. According to the Boulder Country Sherriff’s office, Mackey grabbed onto a large rock to stop his fall. The rock, which weighed about 300-400 pounds, fell on his left leg and trapped him.

After Mackey yelled for help, two nearby hikers were able to pry the rock off his leg, call 911, and give him first aid until emergency services arrived.

“The technical rescue took Rocky Mountain Rescue several hours to complete,” according to the sheriff’s office news release. “They had to traverse a scree field before using a wheeled litter to complete the evacuation.”

Published: May 27, 2015 1:57 PM EDT We may earn commission from links on this page, but we only recommend products we back that following the surgery he underwent on Tuesday, he will be transferred to Denver Health Medical Center for recovery. A steel rod was inserted between his knee and foot.

“I’ve been so lucky in 20 years of doing this stuff that I’m actually OK with it,” Mackey told the news station.