Smith, M. H., & Sharkey, B. J. (1984). Altitude training: who benefits? The Physician and Sportsmedicine, 12, 48-62.

Studies at moderate altitude are not conclusive in demonstrating a beneficial training effect for talented athletes who are already fully trained. Limitations are inherent in conclusions drawn from studies done at various altitudes [because varying degrees of stress invoke different forms of adaptation.]

Responses. When the body is subjected to a hypoxic environment, adaptive processes attempt to facilitate the intake, transport, and use of oxygen.

1. Immediate responses. Ventilation is markedly increased on exposure to reduced oxygen pressure. The body attempts to move greater amounts of oxygen into the lungs by increasing respiratory rate, tidal volume, or both. Breathing is heavier, that is, the athlete works harder at breathing. However, in sports where ventilation is synchronized with work rate (e.g., rowing, swimming, cross-country skiing) tidal volume is altered and provides the needed increase in ventilation without disturbing ventilatory work rate patterns.

   Opinions differ as to whether cardiac output is initially elevated or unchanged.

2. Intermediate responses. The second phase of adaptation deals more with the body's adaptations to increase the oxygen transport capacity of the blood. Changes in ventilatory, cardiovascular, and hematological variables occur.

   Cardiac output is reduced when compared to sea-level variables several days to weeks after exposure primarily through a reduced stroke volume. Once depressed, cardiovascular function remains depressed and does not recover with increasing length of exposure.

   Hematological adjustments occur to augment the oxygen content of the blood. Hemoglobin concentration increases as the plasma volume decreases. RBCs increase due to a hypoxic-sensitive erythropoietic mechanism that alters HB and hematocrit values. The greater circulating volume of Hb increases the oxygen-carrying capacity of the blood.

3. Long-term responses. The pH changes, and other biochemical changes occur as an adjustment to altered internal conditions.

Altitude Training

Maximum aerobic power (VO2max) is a function of cardiac output and arteriovenous oxygen difference. The changes that occur raise the question of whether the altered conditions would increase sea-level performance because of the supranormal condition. The work in this area is conflicting.

Better studies that employ control groups and design considerations do not support any beneficial effect. This has been reported on swimmers:

• Faulkner, J. A., Daniels, J. T., & Balke, B. (1967). Effects of training at moderate altitude on physical performance capacity. Journal of Applied Physiology, 23, 85-89.

• Saltin, B. (1967). Aerobic and anaerobic work capacity at an altitude of 2,250 meters. In R. F. Goddard, (Ed.), Proceedings of the Effects of Altitude on Physical Performance Symposium (pp. 97-102). Chicago: The Athletic Institute.

"One of the major problems with these early studies was the lack of a control group, where an equivalent group underwent the same training program at sea-level. Without a control group, it is difficult to separate an improvement in fitness and performance caused by training from the possible potentiating effects of altitude." (p. 54)

The main difficulty is getting a good control group that is matched on critical potential confounding variables. In one study, one leg was trained at altitude, the other at sea-level in highly trained runners. Thus, subjects served as their own controls. No benefit from altitude was found. [Adams, W. C., Bernauer, E. M., Dill, D. B., & Bomar, J. B. (1975). Effects of equivalent sea-level and altitude training on VO2max and running performance. Journal of Applied Physiology, 39, 262-266.]

Individual response. Statistical analyses of groups may not be the most sensitive tests of effects. It is strongly supported in the literature that some individuals are assisted by altitude training while others are not and even some regress because of the stressful exposure.

The generalization of laboratory measurements to performance potential is also a source of error. The predictive reliability of laboratory physiological measures is not high. The question arises that in the few who seem to be benefited by altitude exposure what are the mechanisms?

1. Several athletes with suboptimal hemoglobin levels have developed a preference for altitude training because it tends to raise their hemoglobin toward the population mean. On the other hand, athletes with already high levels should undergo further increase at altitude could develop a blood viscosity that is detrimental to adequate blood flow (oxygen delivery is reduced).

2. Athletes with borderline iron stores might suffer during the early days at altitude because hard training accelerates RBC production which could deplete already limited iron stores. Combined with a loss of appetite or inadequate dietary iron intake, a serious iron deficiency could result causing a deteriorated cardiovascular function.

3. A preference for altitude training could be based on the simple fact that sea-level work seems easier on return. The reduced demand of sea-level work for an anaerobic component produces this appraisal.

   "A critical reading of the literature casts doubt on the value of altitude training, at least for some athletes." (p. 59)

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