Demystifying Altitude Tents

© 2004 Andy Applegate

For the past several years many of the world’s best athletes have been using altitude tents to simulate high altitude while at rest. This “live high-train low” approach has caused quite a stir among athletes, coaches and scientists. For most athletes, the whole idea of an altitude tent or chamber is a huge mystery. What is all this voodoo about? Does it really work, and if so, how much? We decided to put an athlete inside a tent to not only see if it lived up to the hype, but also to relate exactly what the experience is like. This was by no means a scientific “experiment” – there was no control – simply one athlete giving us subjective and objective data.

Why altitude?

The basic concept of living or training at altitude is to cause the body to adapt to the lower oxygen content and lower air pressure by producing more oxygen-carrying red blood cells and hemoglobin. Theoretically, this should improve the athlete’s ability to perform work, because more oxygen is available to the working muscles. This is an oversimplification and there are many other adaptations that take place, but for our purposes this is what you need to know.

Sleeping in a simulated altitude environment allows the body to achieve some of the positive adaptations to altitude while still permitting the athlete to perform workouts at an oxygen-rich lower altitude where muscles can perform at their normal work level.

The equipment

The two keys to simulating an altitude environment are oxygen content and barometric pressure. An altitude “chamber” reduces both the air pressure and oxygen content, but is generally more expensive and cumbersome than the “tent” systems currently available. For our study we used a tent system that displaces oxygen in the air entering the tent with nitrogen to reduce the oxygen content percentage. This is accomplished with a “hypoxic air generator” outside the tent pumping the conditioned air into the tent. This type of system reduces the oxygen content, but does not affect the air pressure.

The tent itself was an “in home” model measuring approximately 7 feet long by 7 feet wide and 5.5 feet tall, much like a camping tent with clear plastic windows and no mesh vents. Assembly of the tent was quite easy and only took approximately 30 minutes. Hypoxic (low oxygen) air was pumped into the tent via a ¾-inch clear delivery hose that was long enough to allow the generator to be placed in a different room. This significantly reduced generator noise heard in the tent. The percentage of oxygen in the air entering the tent was easily attenuated with a knob on the front of the generator.

The protocol

We had an athlete sleep in an altitude tent for four weeks leading up to a goal race at sea level. The amount of time per day spent in the tent was between eight and ten hours at a simulated altitude of between 9,000 and 10,000 feet. The oxygen content of the air in the tent was monitored upon waking each morning, as was the athlete’s resting heart rate and body weight. Hematocrit was tested before and after the four-week period.

Critical power tests (average power for a specific amount of time) were done the week before tent use and the week after. We also tracked race performance information. We chose CP6 (average power for six minutes) and CP30 (average power for 30 minutes) as tests. CP6 is a good proxy for power at VO₂ max and CP 30 is a good estimate of power at lactate threshold. We gradually increased the sleeping altitude over four nights to 9,000 feet. During the test period the athlete competed in two races per weekend and did one or two hard interval session per week. The remainder of the training was skills and endurance work along with two days per week of weight training.

Adaptation

During the first week of tent use the athlete experienced some very interesting and uncomfortable sensations as his body was adapting to the simulated altitude. During the first few nights, even at a relatively low altitude (4,000-5,000 feet) the atmosphere in the tent became very warm, about 90 degrees F., and extremely humid.

Respiration was markedly increased and the conditions were extremely uncomfortable, resulting in fitful and disturbed sleep. Over the remainder of the first week the temperature and humidity inside the tent subsided as adaptation took place.

After about seven nights, and at our goal altitude, his sleep returned to normal and he even reported sleep to be deep and sound. Resting heart rate was elevated for the first week, but was back to “normal” by the end of the second week.

Another issue was an increased need to urinate. Over the course of the test the athlete also experienced a marked increase in appetite. Caloric intake was increased slightly with no effect on body weight.

It seemed to take two weeks for the athlete’s body to fully adapt to use of the tent. Interval sessions during these first two weeks showed a loss of power and race performance during this time was flat. During the third week a noticeable improvement took place with the interval sessions, and race results were above expectations, all with a low perceived exertion level. At this time the athlete reported deep and comfortable sleep. Tent use was discontinued just three nights before the goal race. During the goal race the athlete felt “powerful” and “in control”. The race result was as good as or better than expected.

The tests

All power tests and interval sessions were done inside on a trainer with an SRM power meter. Here is a summary of the pre- and post-test results for our subject.

            Pre                              Post:               Improvement:

Weight           151lbs                        150lbs              stable

Hematocrit     44.1                            42.6                decreased

CP6                381watts                    399watts        +4.7%

CP30              314watts                    343watts        +9.7%

Other considerations

Due to the increased respiration rate and an increase in urine production, especially during the adaptation period of any altitude exposure, hydration is a major issue. Care needs to be taken to ensure proper hydration in order to maintain the ability to perform in training and racing.

An athlete who is considering embarking on any kind of altitude training regime, whether real or simulated, should have blood iron (ferritin) levels checked. If ferritin levels are low to normal, iron supplementation may be recommended by a doctor. Since excess iron can be toxic, a test should be done to check levels before starting any iron supplementation.

What is the optimum sleeping altitude? At higher altitudes an athlete may experience more beneficial adaptations; however, there is a trade off. The higher you sleep, the more detrimental it will be to recovery from training efforts. Individuals will want to work to find the proper balance between recovery and sleeping altitude. Generally, simulated altitudes of 7,000 feet and above are used. Base elevation and performance goals also need to be taken into account when setting sleeping altitudes.

There has been a lot of discussion about hematocrit (HCT) and altitude exposure. Altitude exposure may increase HCT in some athletes. This is often offset by the decrease in HCT due to a heavy training load, as seen in our subject. For this reason increased HCT is not necessarily a good indicator of altitude adaptation. Performance based testing is a more reliable approach.

Conclusions

For our athlete, under these circumstances, the tent appeared to work well as the athlete improved power at lactate threshold and VO₂ max. It is difficult to say exactly how much of the improvement, if any, was due to the tent and how much was due to training response. A conservative estimate in this case would be approximately a 5% improvement in power at LT, or about half of the total improvement. This would fall well in line with what the manufacturers regularly advertise. The bottom line is that we believe altitude tents can work for most athletes.

Be aware that adaptation to altitude is very individualistic. Some athletes respond much more than others. For this reason if you are interested in trying a tent it might be advisable to attempt to rent or lease a system to first determine if you are a “responder”. We saw in this exercise that the “live high, train low” approach works for competition at sea level, but the implications are even greater for an athlete preparing for competition at altitude.

Is this type of “training” for everyone? Perhaps not. Apart from the price tag (our test system was valued at $7000) there are some serious quality of life issues with sleeping in a tent, especially if you have a less than understanding spouse or pets. While altitude tent systems can be uncomfortable to use and a substantial monetary investment, the performance benefits they may be able to offer cannot be ignored.

Andy Applegate heads a2 coaching and is an elite-level road, cyclo-cross, and mountain bike racer. He is also a USA Cycling and Ultrafit-certified coach. He may be reached at aapplegate@ultrafit.com. For more information check out www.a2coaching.com.

originally published VeloNews Spring 2004