Rémi Bonnet holds the world record for the steepest and most grueling mountain running format on earth: the vertical kilometer. On October 18, 2025, the Swiss athlete raced up the notorious Kilomètre Vertical de Fully course in Switzerland, climbing 1,000 vertical meters over just 1.92 kilometers in an astonishing 27 minutes and 21 seconds. That effort erased a standing world mark by nearly a minute and a half, cementing his status as the undisputed king of uphill endurance.
Most people picture elite runners covering flat marathons or rolling trails. Bonnet operates in an entirely different dimension where gravity dictates everything. Raised in the alpine village of Charmey, Switzerland, his daily childhood routine involved hauling hay and tending to goats on steep mountain slopes, building the unique physiological engine that now dominates international skyrunning and ski mountaineering.
Understanding the Vertical Kilometer Discipline
The vertical kilometer, often abbreviated as VK, is simple to describe and brutal to execute. Competitors must gain 1,000 meters of elevation in the shortest horizontal distance possible. The course in Fully, Switzerland, is essentially an old train funicular track pointing straight up an incline, making it the premier testing ground for absolute vertical speed.
Unlike traditional trail races that reward technical descending skills, a VK is pure upward suffering. You don't need agility on the way down because times are recorded strictly at the summit. Athletes rely heavily on pole power, pushing through their arms as much as their legs to drive their body weight upward at gradients exceeding 45 degrees.
The Anatomy of a Record-Breaking Climb
When Bonnet toed the start line at the 2025 Fully VK event, expectations were high, but breaking the previous record of 28 minutes and 53 seconds seemed almost out of reach. That former mark had stood for eight years, viewed by physiologists as near the human ceiling.
Bonnet didn't just break the barrier; he shattered it by 1 minute and 32 seconds, finishing in 27:21 according to Salomon's athlete profile. His strategy relies on an unmatched power-to-weight ratio and an aerobic capacity forged through a relentless year-round training block.
- Winter Base: From November through April, Bonnet competes on skis as a world-class ski mountaineer, winning multiple ISMF World Championship titles. This builds massive lung capacity without the joint pounding of running.
- Summer Transition: When the snow melts, he swaps skis for running shoes, transferring his winter cardiovascular engine directly onto steep dirt trails.
- Pace Execution: He attacks the steepest sections from the gun, refusing to drop his cadence even as his heart rate hits maximal output.
Year-Round Endurance Domination
Too many athletes specialize in a single season and burn out. Bonnet splits his calendar between ski mountaineering and summer mountain racing, capturing top honors across both disciplines. He won the overall Golden Trail World Series in both 2022 and 2023, dominating iconic races like the Marathon du Mont-Blanc and setting course records at the Pikes Peak Ascent, as detailed on Wikipedia.
This dual-sport approach protects him from overuse injuries. While other runners log massive monthly mileage on flat roads, Bonnet spends his hours accumulating vertical gain at low speeds, which preserves his muscle fibers for explosive race days.
Common Mistakes in Uphill Mountain Running
Many runners trying to tackle steep inclines make fundamental errors that destroy their efficiency. If you're looking to improve your own climbing, watch out for these pitfalls.
- Ignoring upper body strength: Arms are not just for balance on a steep climb. Without proper pole technique, you miss out on pushing up to thirty percent of your body weight with every step.
- Starting too fast: Charging out of the gate on a sustained climb floods your legs with lactic acid before you've cleared the first hundred meters of elevation.
- Wearing the wrong footwear: Standard road shoes lack the deep lugs needed to grip loose dirt and scree on steep alpine slopes, leading to wasted energy with every slip.
Frequently Asked Questions
What is the exact vertical kilometer world record time?
The record is 27 minutes and 21 seconds, set by Rémi Bonnet at the Kilomètre Vertical de Fully in Switzerland on October 18, 2025.
How does Rémi Bonnet train for these events?
He spends winter competing in ski mountaineering—winning world titles on the ISMF circuit—and transitions to mountain running in the summer, focusing on high-gradient uphill intervals.
What makes the Fully course so special?
The course follows a straight, ultra-steep utility line path, offering a pure 1,000-meter vertical gain over a very short horizontal distance without technical switchbacks.
Does Bonnet compete in standard flat marathons?
No, he focuses exclusively on technical mountain running, skyrunning, and ski mountaineering where vertical elevation change is the primary challenge.
