Research Says
A study by David Jeker and colleagues (2020) in the European Journal of Sport Science, examined how altitude and race distance affect uphill vertical speed and running mechanics during an extreme mountain ultra-marathon. Twenty-seven experienced ultra-runners (24 men, 3 women) participated in the 2015 Tor des Géants race, considered one of the world’s most challenging mountain ultras. The race covers 205 miles with 78,740 feet of elevation gain and loss across the Italian Alps, with a maximum altitude of 10,826 ft and 25 mountain passes over 6,560 ft. Runners typically have 150 hours (6.25 days) to complete the course, though this particular edition was stopped at 80 hours due to bad weather conditions.
The researchers attached sensors to participants’ lower legs to measure vertical speed (VS), stride height (SH), and stride frequency (SF) across ten mountain passes at different altitudes. Measurements were taken during specific sections with 482 to 1,207 feet elevation gain, categorized as either low altitude (2,100-6,844 ft) or high altitude (7,848-10,512 ft). The researchers found that runners initially moved faster on the lower altitude climbs compared to the higher altitude climbs, but this difference disappeared after the first quarter of the race as neuromuscular fatigue accumulated. The decrease in speed was more pronounced at lower altitudes throughout the race.
Why It Matters
For mountain ultra-runners, understanding the relationship between altitude, fatigue, and performance is crucial. This study reveals that while running at higher altitudes initially results in slower uphill speeds (likely due to reduced oxygen availability), as the race progresses, the accumulated neuromuscular fatigue becomes the dominant factor limiting performance — even more than the oxygen limitations at altitude. The speed differential between low and high altitude sections eventually disappeared, with neuromuscular fatigue causing a more dramatic speed decrease at lower elevations. The strongest correlation was between vertical speed and stride height rather than stride frequency, suggesting that leg muscular endurance — particularly in the knee extensors — most significantly impacts the ability to maintain pace on climbs during ultra-distance mountain events.
Although not explicitly discussed in the paper, the finding has interesting implications for how we understand fatigue in ultra-endurance events. Exercise scientists have proposed competing theories about what ultimately limits performance: the Central Governor Model suggests brain-regulated fatigue is primary; cardiovascular models focus on heart/lung oxygen delivery limitations; while peripheral fatigue models emphasize local muscle damage. By demonstrating that neuromuscular fatigue eventually overshadows altitude-related oxygen delivery constraints, this study lends support to peripheral fatigue models for multi-day mountain events. The convergence of speeds at different altitudes challenges conventional wisdom that altitude effects would persist or even compound with fatigue throughout a race. Instead, the study suggests there is a crossover point where the primary performance limiter shifts from systemic (oxygen delivery) to local (neuromuscular) factors.
Applied Insights
The study reveals that in longer mountain ultra events, your muscles — especially your quads — become the main performance limiter, rather than cardiovascular fitness. Maintaining the power to push yourself upward with each step matters most as the race progresses.
To train for this, focus on targeted quad-strengthening exercises and muscular endurance workouts. Include squats, lunges, and step-ups in strength training workouts. Integrate long uphill hikes with a weighted pack done at a moderate pace into your long endurance days, and run hill repeats at your lactate threshold pace as part of your run-specificic training on shorter training days.
I’m Thinking
These findings suggest a transition point where neuromuscular fatigue overtakes aerobic capacity/altitude as the primary performance limiter in mountain ultrarunning events. The researchers specifically note that “the effect of aerobic capacity on performance is only reduced beyond 75 km (46.6 miles),” referencing earlier research showing maximal aerobic speed remained the stronger predictor throughout a race up to about 47 miles. Their data indicates this crossover occurs after approximately 51 miles (the first quarter of the Tor des Géants race).
This suggests that for events up to 50 miles (typically 8-13 hours for most runners), aerobic development and altitude adaptation are the most important limiting factors for performance; for events of 100 miles (typically 20-36 hours for most runners) and beyond, while aerobic capacity remains essential, preserving neuromuscular function becomes increasingly critical. The timing of the crossover likely varies with ability level and training status.
Reference
Jeker, David, Mathieu Falbriard, Gianluca Vernillo, Frederic Meyer, Aldo Savoldelli, Francis Degache, Federico Schena, Kamiar Aminian, and Grégoire P. Millet. 2020. “Changes in Spatio‐temporal Gait Parameters and Vertical Speed during an Extreme Mountain Ultra‐marathon.” European Journal of Sport Science 20 (10): 1339–1345. https://doi.org/10.1080/17461391.2020.1712480.
