In my first post on estimating your FTP (Functional Threshold Power), I mentioned that altitude was a factor since FTP is a metric based on aerobic function. The bottom line of that portion of my blog post was that as the altitude increases, aerobic function decreases and so FTP decreases. And as you acclimate to a new, higher altitude your aerobic function and FTP improve, but they never attain the level you would have at a lower altitude.
So how much does increasing altitude decrease your aerobic performance? The accompanying chart is from studies by Basset et al.¹ and Peronnet et al.² to find the answer to that question (click to enlarge the chart). The data comes from world-class road cyclists and runners, so there may well be some population-specific results here. But we can probably use the data with well-trained endurance athletes to get general estimates of the effect of altitude. Peronnet’s data is not divided by acclimatization, but the athletes were probably acclimated given that they were competing at world-class events.
Note the increasing spread in data between the two studies as the altitude increases beyond 5,000 feet (1,516m), with Peronnet’s showing slightly less loss of performance at increasing altitudes. Generally, however, they are quite close.
So as you can see here, if you live and train at about 5,000 feet you could theoretically expect a 5% increase in FTP and performance if you went down to sea level to race. Conversely, if you came from sea level where you live and trained at some place like Denver at about 5,000 feet, you might expect, initially, about a 9% drop in FTP and performance. If you arrived a few weeks early allowing your body to fully adapt, that loss of performance would theoretically and gradually shrink to about 5%.
When traveling to races at a higher altitude, it’s best to arrive days earlier for the adaptation process.
- Bassett, D.R., Jr., et al. “Comparing Cycling World Hour Records, 1967–1996: Modeling with Empirical Data,” abstract, Medicine and Science in Sports and Exercise 31, no. 11 (1999):1665–76.
- Péronnet, F., G. Thibault, and D.L. Cousineau, “A Theoretical Analysis of the Effect of Altitude on Running Performance,” abstract, Journal of Applied Physiology 70, no. 1 (1991):399–404.