Fox, E., Bowers, R., & Foss, M. (1993). The physiological basis for exercise and sport. Madison, WI: Brown & Benchmark. pp. 449-471.

Acclimatization

The longer one remains at altitude, the more performance improves, but it never quite reaches the values that are obtained at sea-level. Acclimatization rate depends upon the individual. There are some who never acclimatize and continue to suffer mountain or altitude sickness while at altitude.

Physiology of Acclimatization

The main reason for lessened endurance (>2 min) performance at altitude is that it is a consequence of the lowered partial pressure of oxygen (PO2). That results in varying degrees of hypoxia (a lack of adequate oxygen), the degrees being dependent upon the altitude.

1. Increased pulmonary ventilation (hyperventilation). This response is immediate upon arrival at altitude, being more pronounced during the first few days and then stabilizing about after a week.

2. Increased number of red blood cells and hemoglobin concentration. This is rapid in the first few weeks and serves to increase the oxygen content of the arterial blood. However, for the total RBC volume to be achieved takes as long as three months.

3. Elimination of bicarbonate (HCO3-) in the urine. Its main function is to maintain blood pH at near normal levels.

4. Tissue level changes. (a) increased muscle and tissue capillarization; (b) increased myoglobin concentration; (c) increased mitochondrial density; (d) enzyme changes that enhance the oxidative capacity.

On first arriving at altitude, trained subjects have no greater advantage over untrained individuals beyond that which existed at sea-level. Being fit does not alter the form or rate of adaptation to altitude.

Altitude has the greatest effect on endurance events, rather than anaerobic activities (they may even be helped -- particularly power events).

The Lexington-Leadville Study. The athlete or team that is highly successful in competition at sea-level should be equally successful at altitude after acclimatization. [Grover, R., Reeves, J., Grover, E., & Leathers, J. (1967). Muscular exercise in young men native to 3,100 m altitude. Journal of Applied Physiology, 22(3), 555-564.]

The Penn State Study. Performance decreases are most pronounced in longer events. Altitude affects the working capacity of the native in much the same manner as it does the newcomer to altitude. UPON RETURN TO SEA-LEVEL, ATHLETES' PERFORMANCES WERE NOT IMPROVED AS A RESULT OF TRAINING AT ALTITUDE. As a matter of fact, performances in one and two-mile events were slower the third and fifteenth days after returning from altitude. [Buskirk, E., Kollias, R., Akers, E., Prokop, E., & Picon-Reategui, E. (1967). Maximal performance at altitude and on return from altitude in conditioned runners. Journal of Applied Physiology, 23(2), 259-266.]

The Michigan-Penn State Study. Performances were not quite as good as at sea-level after acclimatization. The longer the event, the more degraded the performance. Maximal aerobic power did not improve with acclimatization. Upon return to sea-level, one mile performances did improve but two and three miles did not. EVEN AT MODERATE ALTITUDE, PHYSICAL PERFORMANCE, PARTICULARLY IF IT RELIES ON THE AEROBIC SYSTEM, WILL BE IMPAIRED AND WILL NOT ALWAYS IMPROVE WITH ACCLIMATIZATION. [Faulkner, J., Daniels, J., & Balke, B. (1968). Maximum aerobic capacity and running performance at altitude. Journal of Applied Physiology, 24(5), 685-691.]

The California-Colorado Study. VO2max and 2-mile performances were significantly decreased at days 1 and 3 at altitude. Only a slight (2%) improvement in VO2max and 2-mile performance occurred after 18-20 days of acclimatization in altitude performance. Performances equaled but did not exceed pre-altitude values on returning to sea-level. THERE IS NO POTENTIATING EFFECT OF HARD ENDURANCE TRAINING AT 2300 M OVER EQUIVALENTLY SEVERE SEA-LEVEL TRAINING ON SEA-LEVEL VO2max OR 2-MILE TIME IN ALREADY WELL-CONDITIONED MIDDLE DISTANCE RUNNERS. [Adams, W. C., Bernauer, E. B., 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(2), 262-266.

The Ohio State Studies. The ability to perform hard physical work at high altitudes improves markedly during 3 weeks of acclimatization. It does not, however, approach sea-level working capacity during that period. Training volumes at particular intensities at altitude are always compromised over that which can be performed at sea-level.

On studies that show performance improvement. In studies which show improved sea-level performances after altitude training, it usually is not determined whether the improved performances were due to altitude exposure or to the fact that Ss eventually increased their fitness level during the conditioning at altitude. It is possible their performances would have been improved with further training at sea-level. FOR HIGHLY TRAINED ATHLETES, TRAINING AT AND ACCLIMATIZATION TO ALTITUDE DOES NOT IMPROVE RETURN-TO-SEA-LEVEL PERFORMANCE.

MAXIMUM AEROBIC POWER AND PERFORMANCE WITH THESE ATHLETES DOES NOT ALWAYS IMPROVE WITH ALTITUDE ACCLIMATIZATION. One of the major reasons for this might be that the training programs required for these athletes cannot be sustained at altitude at an intensity and volume commensurate with that at sea-level. The degree and amount of beneficial stimulation for maximum performance is reduced. [Kollias, J., & Buskirk, E. (1974). Exercise and altitude. In W. Johnson & E. Buskirk, (Eds.), Science and medicine of exercise and sports. New York: Harper and Row. pp. 211-227.]

Implications

1. Training at altitude might enhance sea-level performance in originally unconditioned, non-athletic individuals. (p. 469)
2. For highly trained athletes, the training intensity required for maintenance of peak performances cannot be achieve at altitude. (p. 469)
3. Altitude training is not a stimulus for further adaptive responses in specific exercises in high-performance athletes.

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