Why Is the Vertical-Kilometer of Fully (Switzerland) So Fast? Physiological and Mechanical Benefits of Stair Ascent on Extreme Uphill Slopes.

Abstract

The world's fastest vertical kilometer course in Fully (Switzerland) is comprised of stairs at a very steep grade (~31°). The aim was to determine whether stair ascent, with and without poles, lowered physiological, mechanical, and neuromuscular demands compared with continuous uphill ramp locomotion at VK-relevant slopes. Twenty-two endurance-trained participants completed randomized treadmill trials at a constant vertical speed (800 m·h-1) in three conditions: uphill ramp (R), stairs (S), and stairs with poles (SP), each performed at six slopes (18-38°). Metabolic power (MP), heart rate (HR), minute ventilation (V̇E), rating of perceived exertion (RPE), internal mechanical work, step frequency, and lower-limb electromyography were measured. At 18°, S elicited greater MP (6%), HR (4%), and V̇E (7%) compared to R (all P<0.001), with no difference in RPE. From 26° to 38°, S elicited less MP (6-10%), HR (5-10%), V̇E, and RPE relative to R (all P≤0.05). Across 26-38°, S involved less internal mechanical work (23-45%, P<0.001), lower step frequency (P<0.001), and reduced gastrocnemius lateralis activity (P<0.001) compared with R. Relative to S, SP reduced gastrocnemius lateralis and vastus lateralis activity (P<0.05) but did not change MP, HR, V̇E, or RPE (all p≥0.09). On very steep slopes, stairs improve uphill economy and reduce rate of perceived exertion, likely through reductions in internal mechanical work and plantar-flexor demand. These findings provide a mechanistic explanation for exceptional performances on VK courses featuring extended stair sections. Using poles on stairs altered the activation of the measured lower-limb muscles, particularly by reducing gastrocnemius lateralis activity, without clear physiological or perceptual benefit at the tested intensity.