High altitude can benefit cyclists in many ways, from increased hematocrit due to sleeping at altitude to increased speed due to reduced air density. But high altitude also means reduced threshold power due to reduced oxygen.
In road bike racing, the competitors are all on the same page by being in the same place, either top or bottom. With the UCI esports world championship, or racing in general, competitors are literally all over the world. And with the Zwift algorithm providing every rider with the same effective air density pattern, there is only one penalty for being at altitude.
An accepted rule of thumb for professional trainers and physiologists is a 1% decrease in threshold power per thousand feet of elevation above sea level down to approximately 5,000 feet. Above that, and the fall gets steeper.
“It’s crazy the impact it has,” said NeXT eSports co-founder Greg Abbott, who was nine runners from six countries at Zwift Worlds. “They could probably use geolocation to improve game performance and that would be totally fair.”
A quick scan of the Zwift Worlds starting roster reveals that most runners are at or near sea level. Zwift declined to provide the riders’ exact locations, citing privacy concerns. For NeXT, however, their highest pilot is Niki Hug in Olten, Switzerland, at 1,300 feet above sea level.
“The effects on your body when running at altitude are higher heart rate and lower power output,” trainer Jake Rytlewski wrote in a post on the subject. “As you get less oxygen to your muscles, your body increases its heart rate to help bring in more oxygen, which means you reach your peak output faster. This leads to Functional Threshold Power (FTP) weaker and also makes it more difficult to recover from maximal efforts.
It’s not just human motors that are affected by oxygen reduction; gasoline vehicles are also affected. An RV resource group claims that a popular diesel engine loses 3.5% power for every 1,000 feet of elevation above 3,000 feet. “A good rule of thumb is that you will lose 10% of rated power every time you gain 3,000 feet in elevation,” Mark Quasius wrote on the RV Tech Library.
Ashton Lambie is the world champion and world record holder in the individual pursuit, which is a 4km time trial. Lambie has raced and trained all over the world at different altitudes, and he chose the high altitude velodrome in Aguascalientes, Mexico for his world record. He said the Bassett chart above tracks pretty well with his own power output changes.
Lambie is also part of the NeXT team, and last year, while training at the Olympic Training Center in Colorado Springs, Colorado, he landed a unique trick, using the altitude chamber OTC to simulate sea level oxygen levels for racing a Zwift Team Time Trial.
“It was for our first round of playoffs around February 2021 I think, and I got it approved by the OTC because USAC sports physiologist Lindsay Golich is a big fan of running Zwift as a workout,” Lambie said. “I was training at the OTC for the World Championships in Berlin, if I remember correctly, but I still wanted to do solid aerobic work.”
“I would say that was a noticeable benefit, but there were also some weird parts, like an incredibly high heart rate immediately dropping from altitude to sea level. We’re talking like 200 bpm for 10 minutes during TTT” , Lambie said. “So if you live and train at altitude, that can definitely be an advantage. [to go race low], but maybe not as huge as people think! You must have the muscles ready to use the extra oxygen, especially for high intensity anaerobic efforts.
Beyond reduced steady-state power, runners at altitude could be disadvantaged in other ways, says Jeff Winkler, a professional trainer who specializes in running and Zwift training.
“The [Bassett study] The table captures production differences, but not how acute recovery rates might be affected,” Winkler said. “For example, if you did a two-minute maximal effort, would you recover faster at sea level or at 5,000 feet? Or if you did an elevation-adjusted effort at both altitudes by going 5% harder at sea level, would the recovery rate be the same or even faster at sea level? I guess recovery would be faster at sea level either way. I’m not aware of any studies, but I haven’t done extensive research.
Sharp recovery aside, Winkler said the shorter the effort, the less impact the elevation has on power output.
“Since the chart reflects the impact on aerobic capacity, it follows that the impact should be scaled with the degree of aerobic contribution to effort,” he said. “Sprint power is generally considered to be do not be impacted by elevation, does it therefore follow that anaerobic efforts are also less or not affected? I haven’t seen any specific studies on this shade either, but it seems like a reasonable application of science.
Repeated alactic and anaerobic efforts are affected because the PCr regeneration system is aerobic and requires oxygen. I just read a study of soccer players that supports these ideas, where although peak speed and acceleration rate are largely unaffected, the average speed of these efforts is decreased due to the recovery effect, and the total distance traveled decreases in matches at altitude.
Winkler pointed out that another virtual cycling software, BigRingVR, can correct the altitude of riders in-game.
“I can have it increase power in-game for speed calculation, but it still reports/records my actual power in the .fit file,” he said. “They just add an asterisk to the time recorded on the leaderboard.”
Zwift currently has no altitude correction.
“It would be quite simple for Zwift to assign a rider a home elevation for a ride, like using GPS data from the Zwift Companion app, and just apply a multiple to the power of the game,” said said Winkler. “While this is an improvement, it probably wouldn’t fully explain the disadvantages of Zwifters at altitude.”