To prepare, Zhan adopted a science-backed approach: morning 20-km runs, afternoon hill repeats on Yuelu Mountain in Changsha with weighted packs, and meticulous study of navigation tools.

"Blindly running won't work. You need strategy," he said. "More importantly, no matter which event you participate in, once you feel uncomfortable, you need to contact the staff quickly."

The Everest 135, however, demanded unprecedented rigor. The race — open only to athletes with 7,000-meter summit experience and rigorous medical clearance — required signing a "life-and-death waiver". Zhan, the sole amateur in the 135-mile category, faced a field of elite international competitors. Armed with dual satellite navigation watches, a phone and backup power banks, he navigated desolate trails where "not a blade of grass grew".