Research Says
A conference abstract titled “Physiological Determinants of Performance in Vertical Kilometer Running” by Forrest Schorderet and colleagues (2026), published in Current Issues in Sport Science, examined the relationship between lab-based physiological measurements and Vertical Kilometer (VK) race performance in elite athletes. Eight members of the Swiss national ski mountaineering team (four men, four women) completed treadmill tests at a 25% slope, then raced the Fully VK course in Switzerland—one of the steepest in the world (1.9 km distance, 1,000 m of climbing, 52% average slope)—10–12 days later. The strongest predictors of race time were maximal vertical velocity (the fastest uphill speed an athlete could sustain on the treadmill), VO₂max (the maximum amount of oxygen your body can use during exercise), and hemoglobin mass (the total amount of oxygen-carrying protein in your blood). Athletes who experienced greater drops in blood oxygen saturation during the treadmill test—a phenomenon called exercise-induced hypoxemia, or EIH—tended to perform worse in the race. Surprisingly, body fat percentage did not significantly predict performance.
Why It Matters
Vertical Kilometer racing pushes your body to its oxygen-delivery limits on extreme uphill terrain. This study shows that how efficiently your body transports and uses oxygen—not just general fitness or leanness—is what separates faster athletes from slower ones on steep climbs. For athletes training for VK events or steep mountain races, the message is clear: your aerobic engine and your ability to sustain speed on steep terrain matter most.
Applied Insights
How to use this research in your training:
- Train on Steep Terrain: Maximal vertical velocity was the single strongest predictor of VK race time. That means the ability to move fast uphill is specific and trainable. Incorporate regular steep-grade sessions into your program — steep trail repeats, hiking with poles at race intensity, or stairmill intervals. Flat running fitness alone won’t get you there.
- Build Your VO₂max: Aerobic capacity was strongly linked to performance. Include high-intensity interval work and threshold sessions to push your VO₂max ceiling higher. This is the engine that powers sustained uphill effort.
- Don’t Obsess Over Body Fat: Body fat percentage did not significantly predict VK performance in this group of elite athletes. Rather than chasing a number on the scale, invest that energy in building sport-specific fitness and vertical strength.
I’m Thinking
The most interesting finding here may not be the most actionable one. Hemoglobin mass — the total amount of oxygen-carrying protein in your blood — was one of the tightest predictors of VK race time. Athletes with more hemoglobin mass were almost always faster. The study also found that athletes whose blood oxygen levels (SpO₂) dropped more during maximal effort on the treadmill tended to race slower, suggesting that for some athletes there may be an oxygen-delivery bottleneck that limits performance on extreme terrain even when overall fitness is high.
These two findings point in the same direction: oxygen transport capacity matters enormously for VK performance. That naturally raises the question of whether altitude acclimation — living, training, or sleeping at elevation — could boost hemoglobin mass and improve performance. There’s a solid body of research outside this study showing that altitude exposure does increase hemoglobin production over time. But this study didn’t test that, and it’s worth noting that these athletes are Swiss national team ski mountaineers who likely already have significant altitude exposure woven into their training history. We can’t say from this abstract alone whether more altitude would help athletes who already train at elevation, or how much benefit recreational athletes at sea level might gain.
The SpO₂ finding is similarly thought-provoking but hard to act on directly. Exercise-induced drops in blood oxygen are largely a physiological characteristic — related to how efficiently your lungs oxygenate blood at very high cardiac outputs — rather than something you can straightforwardly train away. It’s better understood as an explanatory mechanism: it helps us understand why some athletes hit a ceiling in VK performance, not necessarily what to do about it.
On the study’s limitations: the sample size of eight athletes is quite small, and the cohort was exclusively elite. These relationships may look different in recreational or mid-pack athletes. Body fat came close to being a significant predictor but didn’t quite get there with such a small group — that doesn’t mean it’s unimportant, just that the study wasn’t large enough to detect a smaller effect. Future research with larger and more diverse samples would strengthen these conclusions considerably.
Reference
Schorderet, Forrest, Justin Mottet, Antoine Raberin, Nicolas Bourdillon, and Grégoire P. Millet. 2026. “Physiological Determinants of Performance in Vertical Kilometer Running.” Current Issues in Sport Science 11 (2). https://doi.org/10.36950/2026.2ciss028
