Scott Ellis, 55, apparently died of a heart attack as he climbed along Power Line, one of the race’s steepest segments, according to the Denver Post.

A Colorado endurance race of 100 miles, Leadville 100 begins at 10,152 feet and climbs to 12,424 feet. It was Ellis’ 19th time participating in the race.

“The entire Leadville family is saddened by the passing of Mr. Ellis,” said Amy Henderson, spokeswoman for Life Time Fitness, the race’s organizer. “Many individuals graciously suspended their own races to assist Mr. Ellis in his time of need, demonstrating the power of the human spirit and just how much these athletes are part of the special community we have established in Leadville.”

On the same day, a rider reportedly crashed and died at Snow Summit Bike Park at Big Bear Lake in California, and on Aug. 2, 40-year-old Will Olson was killed by blunt force trauma to the chest at the Enduro World Series in Crested Butte, Colo. Yeny Vergara, a 36-year-old cross-country mountain bike racer fatally crashed a few days prior to Olson on the Elevator Trail at Crystal Cove State Park near Laguna Beach, Calif.

“All of us know that what we do is dangerous, but it doesn’t really hit home until something like this happens,” said Alex Pavon (Juliana Bicycles/Flag Bike Rev), of Flagstaff, who was a participant at the Enduro World Series competitior.