Sutton, J. R. (1994). Exercise training at high altitude. Swimming Technique, February-April, 12-15.

Sutton makes some tentative assessments of some of the research literature involved with adaptation to high altitude environments. Several points made are worthy of further consideration because if they were taken out of context without knowing the limitations of their generality, wrong conclusions and inferences could be made, that is, they would be interpreted incorrectly.

It is not clearly stated in the article as to what is "high" altitude. Generally, research involving high altitude focuses on heights of 3,000 m or more. There is less research, and less of an adaptation reaction at moderate altitude (2,000 to 3,000 m). The work referred to generally involves studies of high altitude adaptation. It would be incorrect to assume that the magnitude and timing of adaptations to high altitude are the same as those of moderate altitude.

The physiological changes noted are usually those fostered by extensive exposure to high altitude environments. In practical terms adaptation requires living at the site for at least six months. It is incorrect to infer that beneficial athletic performance effects, if there are any, will develop in a month and can be transported back to sea-level. Generally, the shorter the time spent at altitude, the less dramatic are the adaptations and those which do occur are quite transient.

"The most important physiological adaptations to living at high altitude are increased ventilation of the lungs, increased blood hemoglobin, and enhanced extraction of oxygen by the tissues. Maximal cardiac output is not usually affected by altitude." (p. 12)

Right from the outset, Sutton recognizes that there is no firm evidence to support beneficial effects of altitude training for sea-level performance. (p. 12)

A further factor of concern is highlighted: "Nutrition for athletes at altitude can be a major problem, and weight loss will be significant at moderate to high altitudes" (p. 12). The amount of weight loss depends upon the altitude.

It is important for sea-level athletes to acclimatize to altitude when competing at altitude. In a gross generalization, the author states that at the Mexico Olympic Games, ". . . none of these sea-level dwellers performed in Mexico City as well as did the life-long residents at high altitude." (p. 13)

". . . the benefit of high altitude training does not necessarily translate to improved performance at sea-level." (p. 13)

There are physiological changes which occur at altitude, particularly those which include effects on the transport and utilization of oxygen. To maximize oxygen transporting ability, one needs to optimize all of the links in the delivery, extraction, and utilization phases of the aerobic mechanism. Factors such as ventilation and the central ventilatory drive, which do not limit VO2max at sea-level, may limit performance at extreme altitude.

Physiological responses. "Residence at high altitude and exercise at high altitude will have significant but variable impacts on each component of the oxygen transport chain. . . . Ventilation of the lungs increases and is one of the earliest responses to ascent to altitude. Heart rate and cardiac output during rest and sub-maximal exercise also increase rapidly, and oxygen extraction at the tissue level will reach its maximum rate during exercise at altitude. Later, the number of red blood cells, which contain hemoglobin and are responsible for carrying oxygen, also increases; this adaptive increase continues for a considerable time . . . . The earliest increase in hemoglobin concentration on exposure to altitude is due primarily to a decrease in plasma volume, rather than a true increase in the manufacture of new red cells (erythropoiesis)." (p. 13)

The activities of key enzymes involved in aerobic metabolism in muscle increase, as do capillary and mitochondrial density in skeletal muscles. However, much of the capillary and mitochondrial density increases are not true increases but rather, result from loss of muscle mass. (p. 13)

". . . neither the transfer of oxygen from the lung alveoli to the capillary blood nor the cardiac output appear to be maximally extended by exposure to high altitude." (p. 13)

At less extreme altitudes (e.g., <4,300 m) curious adaptations occur: VO2max will not be increased, although endurance performance while remaining at that altitude will be enhanced. (p. 13) "Strangely, however, the body, as if to compensate for the increased blood oxygen content, reduces the cardiac output and the blood flow . . . so that the total amount of oxygen delivered . . . . to the whole body is actually unchanged following acclimatization." (p. 14)

Effects on performance. One study that is used extensively to justify the benefits of altitude training was conducted by Daniels and Oldridge [Daniels, J., & Oldridge, N. (1970). The effects of alternate exposure to altitude and sea level on world-class middle distance runners. Medicine and Science in Sports, 2, 107-112.] This recounts six world-class athletes living and training mainly at 2,300. After 14 days at altitude Jim Ryan returned to sea-level to run a WR mile (3:51.3 s). The majority of the other athletes also performed personal bests. After spending an additional 14 days at altitude, Ryan returned to sea-level to run a WR for 1,500 m. Also, best performances were produced by the majority of the other athletes. This set the scene for advocating that "not only was training at altitude vital for sea-level athletes to compete at altitude, altitude training also seemed to be worthwhile for sea-level athletes wishing to perform well at sea-level." (p. 14)

Some problems with the Daniels and Oldridge study were:

• the training at altitude was reduced in volume (taper) and increased in pace (specific quality), therefore, training effects could be the principal factor that produced the WRs and personal best performances;
• there was no control group and so the study design was a pre-control experiment which does not allow any conclusion about causality, and
• the variability of results between individuals does not allow one to form general conclusions about any associations in the data.

Apart from a lack of methodological control, the findings of the Daniels and Oldridge study have not been independently verified by other studies. In fact, it appears that the finding is refuted by the consensus of well-designed subsequent studies.

Research shortcomings. Many Olympic coaches have accepted the spurious premise of altitude training (a specific adaptation) somehow benefiting sea-level performance in elite athletes. This misconception largely originated in poor research designs in published studies. Major flaws have been:

• small sample sizes (not good for generalizing results);
• inadequate selection of subjects (few top-class athletes in peak training); and
• lack of randomized subject assignment (results are biased).

The following problems can also be added:

• A failure to control the quantity and quality of work performed at altitude (both sea-level and altitude work have to be similar -- when work is reduced at altitude, it serves as an "unintentional taper" which promotes improved performance, particularly on return to sea-level).
• Length of stay at altitude (some changes which hypothetically might be argued to improve performance do not have time to change in brief, less than one month, stays).
• The actual altitude experienced. Most logged research changes occur at high altitudes (e.g., >3,000 m). However, most athlete training camps are held at low altitudes (e.g., Colorado Springs 2,000 m) which would have little to no affect on physiological changes that might benefit performance. The altitude experienced modifies the nature and level of the adaptation response.

Further complications. When altitude acclimatization is accompanied by added stresses, for example, heat or cold, further demands are made on the body's resources and athletic performance will suffer accordingly.

With increased altitude and ventilation, fluid is lost via the respiratory tract, often an unsuspected route for fluid loss.

Lean body mass and fat will be lost after prolonged periods at high altitude.

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