Brent S. Rushall
San Diego State University
[April 2002]

US Swimming recently circulated claims about three training and recovery protocols: altitude, the live-high--train-low (Hi-Lo) regimen, and nitrogen/hypoxic recovery tents.

Contrary to implications of published research, the communication implied the environmental manipulations were beneficial for swimming performance and seemingly equivalent in effect. It claimed that altitude training in Colorado Springs was a good experience, but coaches were not embracing it. If such training was not possible, the next best option for a team would be to train at sea level and live at altitude (the Hi-Lo regimen). The other similar-in-effect alternative, but most expensive option, was sleeping in a nitrogen tent. One has to ask if this information is correct. Is this a responsible communication that explains how to produce benefits for swimmers and coaches? The initial part of the US Swimming communication was as follows:

USA Swimming has an annual budget that pays for USA National Team members to come to Colorado Springs and take advantage of a great facility while improving their cardiovascular profile via adaptation to altitude. In 2001 not many swimmers took advantage of this budget, and we used the excess funds to purchase two Altitude Sleeping tents from Hypoxico Inc. There is some anecdotal evidence in our sport that the tents are beneficial (Ed Moses), and quite a number of people in other sports are extolling the benefits of the system. There has always been a debate about the value of altitude training, and although recent studies have shown the benefits of altitude (stay at altitude), or Hi-Lo training (stay at altitude & train at sea level), we still don't have that many coaches/swimmers who are pursuing the opportunity. (See related articles at this web site for more information. https://www.usa-swimming.org/programs/template.pl?opt=news&pubid=2222) The reasons are many, but a major one is the logistics of getting to a place where an athlete can use altitude adaptation as a part of the training program. The altitude tents remove the need to travel outside of your home training environment and bring the possibility one step closer. [Email sent by Jonty Skinner, February 06, 2002 - 6:38 PM -- Subject: Altitude Tent training opportunities.]

Table 1 illustrates the six conditions that need to be considered when comparing or equating altitude, Hi-Lo, and nitrogen-tent living and training. The three recovery (living) and training environments are not equivalent or similar, which poses a question of why would they be similarly beneficial for training and performance improvement. The three different environments should not be expected to produce similar adaptations or performance effects, because they present different atmospheric conditions and durations of exposures to those conditions. However, until acceptable research is conducted in these matters, equivocal opinions will continue to permeate the topic.



Atmospheric pressure

Oxygen concentration

Research indications

Altitude recovery

Hypobaria (reduced atmospheric pressure)

Environmental hypoxia-pressure (decreased partial pressure of oxygen due to reduction in atmospheric pressure)

Physiological changes occur

Altitude training

Hypobaria (reduced atmospheric pressure)

Environmental hypoxia-pressure (decreased partial pressure of oxygen due to reduction in atmospheric pressure)and exercise hypoxia

Physical capabilities are reduced while some physiological changes occur

Live high

Hypobaria (reduced atmospheric pressure)

Environmental hypoxia-pressure (decreased partial pressure of oxygen due to reduction in atmospheric pressure)

Physiological changes occur

Train low

Normobaria (normal atmospheric pressure)

Environmental normoxia (normal partial pressure of oxygen) and exercise hypoxia

Physiological capabilities are maximal while some physiological changes occur

Nitrogen (hypoxic) tent recovery

Normobaria (normal atmospheric pressure)

Environmental hypoxia-concentration (decreases partial pressure of oxygen due to reduction of percentage of oxygen in inspired air)

Claims of changes

Normal training

Normobaria (normal atmospheric pressure)

Exercise hypoxia

Physiological capabilities are maximal and some physiological changes occur

Altitude and sea level environments differ in atmospheric (barometric) pressure. It is low at altitude (hypobaria), low when living high, but normal (normobaria) when using a nitrogen tent. It is low when training at altitude but normal when training in the Hi-Lo and nitrogen tent conditions. If what US Swimming says about the environmental equivalencies is correct, then barometric pressure cannot be important and thus, that aspect of being at altitude is not an important factor for training or recovery. It is not the purpose of this commentary to relate the conclusive evidence that demonstrates that atmospheric pressure is a significant stimulus to human adaptation.

Altitude and sea level environments differ in the amount of oxygen that is delivered to the lungs. At altitude, the overall density of air is reduced causing less oxygen, and all other gases, to be presented to the lungs with each breath. The partial pressures of all atmospheric gases are lowered because of lowered atmospheric pressure. This condition can be termed environmental hypoxia-pressure, indicating hypoxia is produced because of reduction in atmospheric pressure. For performance, more breaths would need to be taken to supply a standardized amount of oxygen to circulating blood in the lungs. This condition exists for both training and recovery at altitude, but only in recovery in the Hi-Lo situation. The partial pressure of oxygen is lowered in the nitrogen tent circumstance but for a different reason to that of altitude. In the tent condition, the percentages of gases, mainly through the introduction of more nitrogen, are altered. Increased nitrogen causes the overall proportion of oxygen in inspired air to be reduced. This condition can be termed environmental hypoxia-concentration, indicating hypoxia is produced because of reduction in the concentration percentage of atmospheric oxygen. That is possibly a very different physical stimulus to the reduced partial pressures of altitude gases. However, research has not been conducted to assess the interaction effects of partial pressures of oxygen and atmospheric pressures. Until that is done, it is worthwhile to remain skeptical of claims of equivalency. The mixture of inspired gases during training and recovery are not the same across the three training regimens. If what US Swimming says about the environmentally-equivalent effects on performance were correct, then the gaseous make-up of inspired air in either training or recovery cannot be important. Thus, being at altitude would not be an important factor for training.

Neither atmospheric pressure nor the nature of inspired air is similar across the three environments. Because of that, altitude training would not produce the same effects as Hi-Lo training and would be vastly different to those of the nitrogen tent condition. The body does respond to different environmental conditions in specific differential ways.

For many years, altitude training has been promoted as an environment that stimulates greater than normal physiological adaptations that are beneficial for sea level swimming performance. That belief played a substantial part in the decision to finance a substantial upgrade of swimming facilities at the Olympic Training Center in Colorado Springs in the late 1980s. However, evidence does not support the benefits of altitude training on sea level performance in swimming (Rushall, Buono, Sucec, & Roberts, 1998). Even scientists at ICAR in Colorado Springs substantiated that viewpoint (Troup, 1990; 1991, 1992). One should not expect performance improvements from training at Colorado Springs if previous training has been "sane." Attempts to establish high-performance training squads and to conduct Games' preparatory training camps in Colorado Springs have largely been unsuccessful. The highly successful USA 2000 Olympic Team trained and prepared at sea level. If altitude training was beneficial for swimmers, the following question would need to be answered with positive evidence:

Why aren't there a greater number of successful college and club teams that live and train in altitude environments?

With regard to Hi-Lo environments, initial published results are positive, make some extraordinary claims, particularly with regard to the speed of physiological changes, but replicate the poor experimentation and pseudo-scientific work that plagued altitude-training research for many years. Until the standard of science involved with Hi-Lo environments improves, it is prudent to remain skeptical of the claims of benefits that have emerged in various publications and at conferences. This warning is given despite this writer being one of the original promoters of the concept of Hi-Lo environments for athletic development (Rushall & Pyke, 1990). Researchers who "believe" Hi-Lo is beneficial are the most prolific at publishing positive findings, despite frequently unacceptable research designs and particularly poor control of confounding factors. One major feature that has not been considered in Hi-Lo is that the body is cyclically exposed to adapting to sea level and altitude conditions. It does not adapt to altitude and ignore sea level conditions when in this protocol.

Nitrogen tents are a money-making proposition. Their effects are confounded by infomercials, anecdotal evidence, paid testimonies from successful athletes, and particularly poor research. The basic question that must be asked of these tents is this:

If physiological adaptations occur during 8-12 hours of hypoxia in the tents, why don't those transitory adaptations readapt to normal conditions when outside of the tents (whether training or not) for a similar or longer period?

The human body is not selective in its adaptations. It responds dynamically and continually to all environmental changes. As with Hi-Lo advocates, the implication of the tent-promoters is that the body responds adaptively in the tents and then waits for the next tent-experience to continue the adaptation. The training and daily living experiences of normoxia and exercise induced hypoxia are somehow ignored despite the exposure of athletes to that set of conditions usually for greater periods than that spent in tents. The body will be just as aggressive at adapting to normal conditions as tent conditions, which alternate daily. It is absurd to advocate that tent-adaptations will only occur in that contrived environment and will be sustained despite greater exposure to "normal" environments.

Until research is conducted objectively and properly, the effects of Hi-Lo and nitrogen tents, if any, will not be truly known. There are likely to be other factors not considered in these regimens that are beneficial to performance. Increased rest and sleep in recovery are two that come to mind.

What Does This Mean for Swimming/Sport Coaches?

If US Swimming's advice has some merit, that is, that benefits for swimming are derived from altitude, Hi-Lo, and nitrogen tent habituation because they are in essence interchangeable (similar), then contradictions are involved.

  1. If altitude training is beneficial, then neither Hi-Lo nor nitrogen tent environments are likely to be as beneficial. The constant hypoxia-pressure and hypobaria of altitude living/training does not exist in either of the other two protocols. In the Hi-Lo condition, only recovery is equivalent to that of altitude, and in the nitrogen tent, only hypoxia-concentration in recovery is somewhat similar. Both Hi-Lo and tent conditions have more difference than similarity to an altitude-training environment. It is incorrect to equate the three environments, let alone their effects upon physiology, and to a much lesser extent, performance.
  2. If the Hi-Lo protocol is beneficial for swimming, then altitude training or nitrogen tent environments are not likely to be as beneficial. Altitude training promotes less quantity and more stress in training. Hi-Lo recovery is similar to that of altitude. The nitrogen tent only approximates the hypoxia of recovery. Both altitude and nitrogen tents have greater difference than similarity to Hi-Lo environments.
  3. If the nitrogen tent protocol is beneficial for swimming, then altitude training or Hi-Lo environments are not likely to be as beneficial. Following with similar premises to those included in the two previous points, the nitrogen tent protocol only presents unique recovery hypoxia. It provides no experience of hypobaria, which suggests that altitude is irrelevant to an athlete's adaptation.

Until appropriate research is conducted, one should be skeptical of US Swimming's claims although those claims may have been made with the best of intentions. The human body adapts specifically and uniquely to minor variations in environmental circumstances. The atmospheric differences between the three conditions discussed are large enough to suggest that there could be as many differences between them as there are similarities. Confound that situation with the great range of individual differences that exist in the swimming population and the possibility of a claim of general effects on training and performance is even further removed. The implication of US Swimming's stance on altitude, Hi-Lo, and nitrogen tent protocols is circumspect and should be treated with caution.

The most important lesson from this consideration is BEWARE! One could opine that another costly fad is being proselytized to swimmers and coaches. The true situation is not that which has been communicated. Wait until the truth is known before investing in another useless device touted as being important for swimming improvement. It is quite likely that this US Swimming proclamation will go the way of lactate testing, biopsies, and body suits -- all expensive accoutrements that have little to do with improving performances in races that count. For the time being, swimmers and coaches could spend their funds better rather than follow this questionable assertion from US Swimming.


  1. Rushall, B. S., Buono, M. J., Sucec, A. A., & Roberts, A. D. (1998). Elite swimmers and altitude training. Australian Swim Coach, 14(4), 22-33.
  2. Rushall, B. S., & Pyke, F. S (1990). Training for sports and fitness. Melbourne, Australia: Macmillan Educational.
  3. Troup, J. (1990). The effects of altitude training on sea level swimming performance. International Center for Aquatic Research annual - Studies by the International Center for Aquatic Research, 1989-90. United States Swimming Press, 1750 East Boulder Street, Colorado Springs, Colorado, USA 80909-5770.
  4. Troup, J. (1991). The time course of physiological adaptations made during altitude training. International Center for Aquatic Research annual - Studies by the International Center for Aquatic Research, 1990-91. United States Swimming Press, 1750 East Boulder Street, Colorado Springs, Colorado, USA 80909-5770.
  5. Troup, J. (1992). Physiological time course adjustments to endurance training at altitude and tapering at sea level. International Center for Aquatic Research annual - Studies by the International Center for Aquatic Research, 1991-92. United States Swimming Press, 1750 East Boulder Street, Colorado Springs, Colorado, USA 80909-5770.

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