How altitude affects cycling performance
The basics of altitude work like this: as you go higher the air becomes less dense, which means the oxygen molecules are more spread out. As a result, when you breathe in and fill your lungs, there are fewer oxygen molecules in that volume of air. Most people from sea level don’t notice any difference at elevations up to about 5,000 feet above sea level, and between 5,000 and 8,000 feet most healthy people feel perfectly fine at rest and might get out of breath more quickly while exercising. The impact of “moderate” elevation is relatively minor because your lungs are very good at extracting oxygen from air, and even as the air gets thinner you’re still able to satisfy the body’s needs.
Once you get above about 8,000 feet, things are a bit different. At these higher elevations people who normally live at sea level get out of breath just walking up a flight of stairs. Your heart rate and breathing rates at rest will be slightly elevated as your body tries to pull more air through the lungs so it can grab the oxygen it wants. And when you exercise you reach your maximum sustainable pace or intensity level much more quickly than at sea level. This means that if you can produce 250 watts of power on the bike at lactate threshold at sea level, at 8,000 feet above sea level you’ll likely reach lactate threshold at about 225 watts (a 10% decline). You’ll be slower riding uphill, or you’ll need to push yourself harder than normal to achieve the same speed you can hold on a climb at sea level.
As you go from 8,000 feet to 10,000 and then to 12,000 feet, your maximum sustainable power output declines even further. Power meters on the bikes – both road bikes and now mountain bikes as well – enable us to measure the extent of the decline. As riders approach the 12,000-foot summits of Columbine Mine (Leadville 100), and Cottonwood Pass and Independence Pass in Colorado, their maximum sustainable power output is about 70-80% of what it is at elevations below 5,000 feet. To put that in perspective consider this: At sea level a pro might have a lactate threshold power output of 350 watts, and a fit weekend warrior of the same bodyweight might have an LT power of 275 watts. At 12,000 feet that pro’s LT power may come all the way down to 245-280 watts; even to the supermen of endurance sports, high altitude is like kryptonite.
It gets worse. Up to now I’ve been talking about max sustainable pace or power. But the worst thing about racing at high elevations is what happens when you dig deep to go even faster – like when you attack to break away or win a mountain-top finish. At lower elevations extreme efforts are difficult, but your body can recover fast because you can get a lot of oxygen to your muscles very quickly. At high elevations, however, extreme efforts exact a much heavier cost. When you push yourself over your sustainable limits for too long, your power output suddenly goes way down, you pant uncontrollably, and slow to a crawl. That can happen at sea level too, but it passes quickly. At high elevations it can take several minutes to recover from hard efforts; by which time you may have completely lost contact with the pack.
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Preparing to Train and Compete at Altitude
Our understanding of the impact of altitude on performance has improved dramatically in the past 40 or so years (the 1968 Olympics in Mexico City was a major turning point in the science of altitude training). Here are some of the ways LT100 and USAPCC racers cope with the elevation:
- Acclimation: Spending time at higher elevations enables the body to adapt and increase the number of oxygen-carrying red blood cells. This improves your ability to deliver oxygen to the brain and working muscles at all levels of activity, including high-intensity exercise. But true acclimation can take three weeks or more, so it’s often unrealistic to schedule.
- Altitude Training: It is difficult to train and recover optimally at high elevation, so some top athletes strategically plan exposures to altitude (spending a few weeks living and training at higher elevations) throughout the year. This enables them to gain the cardiovascular benefits of acclimating to altitude, and then return to sea level where they can train at higher intensities and recover from training more effectively.
- Acclimatization: (different than acclimation in that it requires proactive steps) Some athletes use specially-designed tents or rooms that simulate the conditions of living/sleeping at high altitude. For some athletes, this can produce an increase in red blood cell count similar to actually spending time at altitude. But the results are highly individual – some people are “responders” and see a benefit, while others do not.
- Hydration: The air at higher elevations is very dry, so sweat evaporates quickly and you lose a lot of fluid moistening/humidifying the air as it enters your lungs. As a result, you dehydrate very quickly at higher elevations. That means less fluid in your blood, which in turn can lead to a higher heart rate because your body has to move the remaining volume faster in order to continue delivering oxygen to working muscles and your brain. If you don’t increase your fluid intake throughout the day you’ll soon have a headache. If you don’t drink enough while exercising, your power output and performance decline very quickly.
- Pacing/Power Meters: Altitude changes racing strategies because some athletes cope with the conditions better than others. Riders who live at high altitudes or who have spent time adapting to high altitude have an advantage, and they can push the pace to put their low-altitude rivals into difficulty. But all riders have to understand where their limits are and be careful about when and how often they exceed those limits. For athletes who don’t have time to adapt to altitude before coming to ride/race at higher elevations, it’s important to be conservative with pacing so you go as fast as you can handle without pushing yourself to the point where you’ll have to suddenly slow down and recover. This is where power meters on the bikes become very useful, because they help riders gauge their efforts.
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