STILL NO CONCLUSIVE EVIDENCE OF ALTITUDE BENEFITS
Wolski, L. A., McKenzie, D. C., & Wenger, H. A. (1996). Altitude training for improvements in sea level performance: Is there scientific evidence of benefit? Sports Medicine, 22, 251-263.
Altitude acclimatization invokes some physiological changes which are similar to some of those which accompany endurance training. This is the hypothesis which is used to assert that altitude training improves endurance performance at sea-level.
The acclimatization and training changes that are similar are increases in myoglobin, hemoglobin level, hematocrit, and aerobic enzymes in the muscle.
Initial exposure to altitude is characterized by a variety of functional changes that together facilitate oxygen transport to partly maintain tissue PO2 and oxygen consumption. Increased ventilation reduces the partial pressure of carbon dioxide resulting in increased alkolosis which then stimulates an increase in renal bicarbonate secretion. With acclimatization, the acid-base balance of the blood is restored and ventilation decreases. Arterial oxygen saturation also increases.
Erythrocyte infusion (blood doping) improves exercise performance and increases maximal oxygen consumption at sea-level. Over time, altitude exposure causes an increase in red cell volume and at first glance appears to be a natural form of blood doping. However, the initial red cell concentration increase is due to a reduction in plasma volume which occurs almost immediately upon altitude exposure. Despite an increase in oxygen carrying capacity per unit of blood, the system has not increased in capacity and the greater blood viscosity results in an increase in workload on the heart. This is the opposite of what happens with endurance training where plasma volume increases. The rate of erythropoiesis is governed by the severity of the altitude stress, being accelerated the higher the altitude. After 4 to 7 days, real hemoglobin levels start to increase. The rate of increase is about 1% per week up to 12%. Thus, to maximize this factor a stay of at least 12 weeks would be necessary for the total change to occur. This is a time period that is generally much longer than the traditional altitude camp.
After reviewing the literature, the authors conclude that ". . . it still remains to be proven that the most important changes invoked by altitude training for improving sea-level performance are hematological" (p. 254).
A difficulty with altitude training is athletes may not be able to maintain the same training intensity as at sea-level and eventually may show a decrease in aerobic fitness after acclimatization and training (p. 254). Also, when oxygen availability is potentially limiting, as occurs at altitude, the rate of anaerobic metabolism increases at higher intensities of exercise. Thus, altitude and sea-level performances of the same quality will differ because they are energized by different proportional contributions of the energy systems.
The increases in aerobic enzymes, myoglobin level, hematocrit, hemoglobin, and muscle buffering capacity from altitude acclimatization are similar to those of endurance training. However, those benefits might be offset by the significant reduction in plasma volume, total blood volume, and VO2max.
Altitude training forces a reduction in workload which may offset any benefit of altitude exposure. To produce physiological changes that could have the greatest similarity to a sea-level endurance training response, the recommended altitude is between 2,200 and 3,500 m. Red cell mass does not increase until an altitude of 2,200 to 2,500 m is experienced. Physiological changes that theoretically could improve sea-level performances are unlikely to develop at altitudes below this range. [Editor's note: at least one study has shown that trained athletes are possibly more sensitive to altitude stimulation and that adaptations occur at lower altitudes (Gore, C. J., et al. VO2max and arterial O2 saturation at sea level and 610 m. Medicine and Science in Sports and Exercise, 27(5), Supplement abstract 42, 1995).] Above elevations of 3,500 m, the decrement in work capacity is too great to be offset by any physiological changes which could be beneficial. Thus, the altitude of exposure seems to have to be one which minimizes workload decrements but produces greater benefits from physiological enhancements. That is purely speculative.
There is no clear evidence that continuous or intermittent exposure to altitude provokes a better form of exercise response.
The latest "spin" on altitude training is the "live high and train low" hypothesis which limits effects to altitude acclimatization rather than acclimatization and training effects. The research in this field is sparse and, as with a large proportion of altitude research, suffers from poor experimental design considerations.
". . . it has yet to be proven that acclimatization to altitude and the subsequent physiological changes improve sea-level exercise" (p. 258).
With descent from altitude there is an immediate decrease in red blood cell production and inhibition of erythropoietin activity. Even though some hematological parameters may remain elevated for some time after altitude exposure, the increases do not transfer to improvement in exercise performance either immediately after descent or one to two weeks post descent (p. 259). There even is a possibility of deteriorated performance several months after altitude training due to the depression of red blood cell production and its potential anemia.
Not all athletes respond in the same way to altitude exposure. Thus, the same type of training camp may not be suitable for different athletes as their response to the environmental conditions will be highly individual.
As has been alluded to above (Gore et al.), highly trained athletes respond differently to altitude exposure than lesser-abilitied and untrained individuals. This altered response needs to be investigated fully because altitude acclimatization, long or short term altitude acclimatization could have effects on performance that have not yet been objectively measured.
Research shows that short- or long-term altitude exposure does not affect maximal force output, fast-to-slow fiber motor unit ratio, or motor activation pattern during isometric exercise. However, muscle buffer capacity is increased. It would seem logical to assert that anaerobic athletes may benefit from altitude training.
"However, the actual training for anaerobic events usually consists of repeated sets of high intensity activity interspersed with low intensity recovery periods. During the recovery periods, the aerobic energy system plays the primary role in the replenishment of adenosine triphosphate and creatine phosphate stores and lactate removal. Thus, the volume of alactic and lactic anaerobic training may be subject to the same limitations as aerobic training at altitude if absolute training time must be maintained. Recovery periods between anaerobic bouts would have to be extended when training at altitude to allow for the same extent of recovery as at sea-level" (p. 260).
Conclusions. "Altitude training studies have shown that some of the changes induced by altitude exposure are similar to those induced by endurance training, however, the mechanism by which some of these changes occur may be totally different. Regardless, elite athletes have focused on the similar end result and train at altitude in an attempt to attenuate the training response and consequently improve sea-level performance. Many of the studies in this area have severe limitations that compromise the conclusions that can be drawn. However, anecdotal evidence cited in the literature shows that many coaches and athletes still believe that altitude training works. Thus, the issue of whether altitude training enhances sea-level performance remains a controversial topic. At the present time, there is no evidence in the scientific literature to suggest that altitude training could benefit any type of athlete who is interested in improving sea-level performance" (p. 261).
Implication. The die is cast. With regard to altitude training benefiting sea-level performance, one has two choices: accept the persistent failure of scientific investigations to support any benefit or follow the often hysterical fervor of devoted coaches who are convinced that it is beneficial.
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