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

PURPOSE: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.