Long-time followers may recall an article I wrote way back in 2004 titled, the Altitude Applecart. No article before or since has seemed to garnered as much impact as that one did for no particular reason, I suppose. However, like so many things, altitude performance was and still is an area of great interest to me because it represents an extreme environment where hours, days and years of preparation can dissipate into an oxygen-deprived hallucination. More recently, extended training camps at altitude have renewed discussion on if and how extended periods of time living at altitude can improve performance. Interestingly, altitude training could be potentially used to mask EPO use, but that’s another topic I won’t cover. The purpose of this updated article is to explain why altitude limits performance, and what you can do to prepare for competition at altitude.
Physiological Effects of Acute Altitude Exposure
Possibly the most common misunderstanding about altitude is the belief that high altitude air is “thinner”, or contains less oxygen. However, the air on Mt. Everest contains the same percentage of oxygen, carbon dioxide and nitrogen as the air I’m breathing in Richmond, albeit without as much pollution. What is different is the barometric pressure (PB). Case in point, I’m pretty much at sea level here on the Cape and my barometric pressure is approximately 760 mmHg. Compare this to the summit of Mt. Everest (~29,000 ft) where barometric pressure is only 200 mmHg. Great, the air pressure is less, but what does that have to do with athletic performance at altitude? Everything! To understand why PB important we need to understand how our lungs and muscles deal with oxygen and carbon dioxide.
When we breathe, oxygen (among other gases) enters the lungs and gets picked up by the blood through the interaction of tiny air sacks in the lungs (alveoli) to the capillaries, whereas carbon dioxide carried by the blood gets dumped off in the alveoli to be exhaled. The rate of diffusion is driven by gas concentrations (i.e., the amount of a gas in a particular space) and is affected by barometric pressure; when pressure decreases gas molecules expand and thus take up more space within a given area. So while the percentage of gases is the same, the actual concentration is lower at altitude.
It is this last fact that is at the heart of your decreased performance at altitude, because as blood passes through the lungs it needs a certain amount of time to transfer gases. At sea level, transit time (of blood passing by those air sacs) is rarely so short that problems arise (assuming you’re an average healthy Joe), but when exercising at altitude transit time is a factor because gas concentrations are lower in the lungs (remember the gas molecules are bigger now). Figure 1 depicts this effect. The lower gas concentrations are why your breathing rate increases when you first arrive at altitude. Other changes occur, as well, and are outlined in table 1. Unfortunately, these changes just aren’t enough compensation at a mile or more above sea level.
Now that you’re armed with an understanding of some of the atmospheric differences and physiological responses, its now time to delve into WHY performance goes down. Obviously, with less oxygen being delivered to the muscles, your ability to produce power goes down steadily as altitude increases. Based on research by Bassett et al. (1999) we can estimate how much you stand to lose off your threshold power output by looking at figure 2.
This figure illustrates a few things. First, even at ~3000 ft (1000 m) you lose about 5% in power output. A second more subtle change is that past 1500 m, power drops a little bit fast per 500 m. While every athlete varies in their response to altitude, even from exposure to exposure, the 1-mile mark (~1600 m) is a boundary where performance really starts to suffer (nearly 10% drop). The reason for this goes back to oxygen transport, and in particular oxygen saturation of hemoglobin (Hb); depicted in figure 3. The lower pressure 1-mile up means that only about 80% of your Hb is carrying oxygen (vs 98% at sea level); at 7000 ft (e.g., Flagstaff, AZ, XTerra USA in Utah) less than 70% of the Hb is carrying oxygen. The body tries to compensate by increasing ventilation (air in and out) which shifts the curve to the left, flattening it for a time. However, when the hill steepens, oxygen carrying decreases, and with it, power. There are many adaptations that occur as you acclimatize, but the most important one, increase red blood cells and Hb, takes about 14 days to really make an impact. A fully acclimatized athlete could see little, if any significant drop at, and definitely below lactate threshold, which can have significant implications for race planning.
Strategies for Racing at Altitude
Riders planning on competing at altitude often consider early arrival to acclimate, but most misunderstand what is needed to do so. Current research supports to approaches:
- BEST: Arrive 14 – 30 days prior to competition, but continue to train mainly at sea level. Athletes considering any major competition at altitude would be best served by this strategy.
- NEXT BEST: Arrive about 7 days before competition, mixing some altitude and sea level training, if possible. It is believed that in this short period of time, ventilation plays a key role in performance improvement (Fulco et al. 2009).
- PRACTICAL: Arrive 48-72 hrs before competition and continue your taper. Current research, including Weston et al. (2001), indicate that after 48 hrs you start to improve, while arriving 6 hrs before leads to the largest decrease.
Obviously, strategy 1 is nearly impossible for most, and strategy 2 also unlikely, which leaves strategy as the most practical approach for the masses. The reason being that the body’s initial response is to improve oxygen delivery to the muscles by increasing ventilation and plasma volume. The loss of body water can be compensated for by concerted efforts to hydrate, but the dehydration may decrease muscle size making it easier to unload oxygen from the blood to the muscles. However, this short time period still falls well short of extended acclimatization, so race strategies should be modified. Further, activities like swimming, have been reported to be more difficult because of the restrictions on breathing even at sea level. Therefore, it is best to use this short adaptation period to determine how you will respond at race intensity.
In my next article, I will take the hypothetical and apply it to Lachlan Morton’s recent Everesting Record. Here you will be able to see why moderate altitude in elite athlete performances like this might not be so impactful.
The goal of this article is to provide athletes with a better understanding of what happens to the body at altitude and how to compensate for those changes to optimize one’s training and/or performance with consideration to their budget. Competition at altitude can be intimidating, but adequate preparation can help mitigate its effects improving one’s performance. For those unaccustomed to altitude and unable to allow for full acclimatization (2-4 weeks), a few training rides at altitude can educate you on your individual response and helping prevent any race day confidence loss when you don’t feel like your usual self.
From the original Altitude Applecart article:
Live High, Train Low
No doubt many of us have heard the title phrase, but my experience has shown that most cyclists still believe that training at high altitude is some how superior to sea level training. Unfortunately, research on this issue is clear; extended training periods at high altitude (1 mile or more above sea level) often leads to DECREASED performance. When you consider that your performance will always be lower at altitude than at sea level, then the reason why performance goes down is pretty clear. If it isn’t consider this example:
Joe Ryder needs to train at 320 watts to improve his aerobic power (AP) while at sea level because its about 20 watts over his threshold (i.e., it creates and overload on his body) and training at this wattage feels very hard and elicits a heart rate (HR) of 180 beats. Now Joe spends 2 weeks in Utah (~6000 ft) and continues his AP training, but repeatedly finds that he can only hold 270-280 watts, despite his HR being over 180 and his effort very high. Upon return to sea level, Joe finds that his AP decreased to 300 watts and no change in threshold.
This example, while a bit extreme, indicates the problems of training at altitude; namely, your effort feels sufficient, but your output is lower. To put it another way, you’re doing less training relative to the overall load on your body. If you reduce your load, you can actually detrain and lose fitness. This is exactly what happens with long-term training at altitude. This is also the premise behind the Live high, train low strategy; by living high, your body adapts to the reduced oxygen availability, but you train low to maintain your optimal intensity, thereby gaining the best of both worlds. Clearly, this strategy holds true for either race preparation, or training camps.
Of all the articles I have written over the past year, none garnered more inquiries than The Altitude Applecart. Due to the large number of contacts I received regarding this article, I felt it useful to revisit the subject and address some the questions I have received. If you have not read that first article, I strongly suggest you read it first before continuing with this article.
Question: What is the Applecart you describe?
Answer: A lot of people asked me this and what it came down to is too many graphics in the article. My original concept was to show a cart full of different apples representing the issues one faces regarding altitude. I eliminated that graphic, but the title stuck because it was catchy.
Question: How much of a disadvantage does competing/staying at 3000-7000 feet (~1000-2110 m) cause?
Answer: This is tough to answer, because each person is different as is their response. One way to find out is to travel to an area that has a climb that goes above 5000 feet. Many areas of the country are near some high altitude climbs. The idea here is to be mentally prepared for how you’ll respond, possibly driving to the top to spend some time and then heading down and climbing back up at and above lactate threshold. This will also give you an idea of how much you’ll be “hurt”. That said, expect to lose 10-20%.
Question: How can I prepare for a stage race held at altitude if I can’t acclimate?
Answer: Again, I think the previous answer is your best strategy if you cannot acclimate. You will also need to be more cognizant of your fluid intake because water losses are higher at altitude. Also keep in mind that the unacclimatized athlete produces more lactate at any given power output while at altitude which is indicative of greater glycogen (stored carbohydrate) use. This means that even relatively easy rides use more glycogen requiring an increase in carbohydrate consumption.
Question: How long will I need to spend at altitude to gain any real blood acclimatization and performance enhancement? What is the best strategy for acclimatization.
Answer: The latest research* indicates that it takes at least 12 hours a day for 3 weeks at an altitude (actual or simulated) of nearly 7000 feet. It also appears that living High and training Low (or with supplemental Oxygen) is the best protocol for enhancing performance. However, it is still unclear whether training at altitude or intermittent, short term severe hypoxia is of any benefit to performance. That said, the more time you have, the better. Moreover, it is better to stay at the altitude you plan to compete at, rather than a lower altitude – it goes without saying
*Rusko H.K., H.O. Tikkanen, J.E. Peltonen. Altitude and endurance training. J Sports Sci. 22(10):928-45