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Curtin University
School of Physiotherapy

Athletic Training at Altitude

Proposition for Debate - by Phoebe Cheuk

Contents

Statement of the Topic

Athletic training at altitude

Introduction

In order to improve athlete's physical performance one of the methods is to have athletes train at high altitude. There is no doubt that physical training at altitude is a must for success in competition held at altitude. However, whether altitude training also improves the performance at sea level is still controversial. Interestingly, almost all endurance athletes used altitude training to prepare themselves for the Olympic Games in Atalanta, which were held near sea level. A new approach of living high and training low (LHTL) is reported to be beneficial in enhancing physical performance. In this paper, the physiological response of altitude exposure and the potential benefit will be discussed. Then the practical aspect of altitude training with respect to duration and relative altitude of exposure will be addressed.

Altitude exposure

The oxygen concentration in air at both sea and altitude is 20.93%. However, the PO2 is directly reduced to the proportion of fall in barometric pressure during ascent. The immediate physiological adjustments to altitude are stimulated by the decrease in PO2 and arterial hypoxia. Acclimatisation is the body adaptation to physiological and metabolic demand by improving the tolerance to changed altitude. The rate of acclimatisation varies among individuals and depends on the change in altitude. There are several physiological changes occurred when an athlete exposure to a higher altitude, they are classified as follow:

Haematological changes

In native altitude resident, a significant increase of red cell volume as well as haemoglobin concentration and hematocrit value is found above 2500m. During the first few days of ascent in altitude training, the red blood cell becomes more concentrated in the plasma. This is due to fluid shift from the intravascular space into the interstitial and intracellular spaces. The hypoxia causes an increase in heart rate and renal blood flow, decrease antidiuretic hormones and plasma volume.

Altitude exposure can in fact act as a natural blood doping by increase red cell mass. These depend on a decrease in plasma volume and secondary to it, polycytemia (an increase in the total red blood cell mass) leads to increase in the blood capacity to transport oxygen. The increase in red blood cell mass with acclimatisation to reduced PO2 in altitude is mediated by the hormone erythropoietin, which is released by the kidney. Some investigation of altitude training found that the increase in red cell volume amount is 10% on average. This is only slightly more than after sea training in non-athletes (8%). Besides, only modest rise of serum erythropoietin concentration could be measured. Other studies found that increase in haemoglobin between sea level resident and high level resident is about 12%. The increase in haemoglobin occurs after approximately 4-7 day of altitude exposure. The critical altitude is somewhere between 1600 and 3000m.

Stray-Gundersen and co-worker has conducted a study to investigate the red cell mass and VO2 max after altitude training. The athletes have first had a 4-week training camp at an altitude of 2500m. One group trained at that altitude and another group trained at a lower altitude of 1300m. Resulted showed that the red blood cell mass and sea level VO2 max increased significantly when compare to the sea level control group. Another study also supported this argument. A 6% increased in red blood cell mass was found following an altitude training of 2200 to 2300m. This study also found that serum erythropoietin typically peak within 2 to 4 days at altitude. Their data also showed that the individual red blood cell mass response is related to the availability of iron and the ability of bone marrow to produce red blood cell.

Cardiovascular changes

The function of cardiovascular system is for transportation of oxygen and removal of carbon dioxide from the body tissue. As altitude increase, a decrease of partial pressure of O2 resulted. This result in a decrease PO2, decrease the arterial oxygen saturation and hypoxia is resulted. The body compensate by increase cardiac output. The cardiac output has been reported increases by 20 % at rest and submaximal exercise, but not the maximal cardiac output.

One study showed that left ventricular end systolic diameter of subjects that undergo a living high and training low (LHTL) programme was smaller. In this study, 21 subjects has been recruited and divided into two groups. One group lived at an altitude of 1980m for 12 hours a day and duration of 2 weeks, and then they trained at sea level. Result showed that LHTL improved the contractility of left ventricle as the end systolic diameter was smaller. In addition, stroke volume and cardiac output in LHTL increased. The improved contractility of the left ventricle might be a result of improved myocardial energy utilisation, but the mechanism is still unknown. The authors also showed that the effect of hypoxia produces dilatation in coronary vessels. Due to the hypoxic vasoconstriction in lung vessels, the right heart compensated by pump against an increased resistance during acclimatization. Another positive effect might be a stimulation of capillary growth, which has been observed with lowering heart rate in animal.

Respiratory responses

Athletes that born and raised at a median altitude of 2000m above sea level have a superior performance in distance running. Much investigation has focused on the four steps of oxygen transport system, namely alveolar ventilation, lung diffusion, circulatory oxygen transport, and tissue oxygen extraction. The peripheral chemoreceptor senses the hypoxia during ascent and stimulates the hypoxic drive to increase the ventilatory rate. The respiratory muscles must be under more stress at altitude than at sea level because of the marked hyperventilation.

An increase alveolar O2 concentration and a decrease in alveolar CO2 are gained from hyperventilation. As a result, arterial PO2 is increased. With the effect of increase haemoglobin concentration, the total amount of O2 in the blood will increase significantly. This may be the explanation of the decrease in CO2 in some cases.

2,3-diphosphoglycerate is produced with the red blood cell during anaerobic reaction of glycolysis. Studies showed that the concentration of 2,3-diphosphoglycerate increased with altitude training. Therefore, a right shift of oxygen dissociation curve resulted. With increased quantity of haemoglobin and red blood cells, tissue oxygenation improved.

VO2 max is usually measured to detect athletic improvement. The lack of consistency of result in VO2 max could be due to various reasons in some studies. VO2 max is related to training pace and training stimulus at altitude. Training pace is decreased at altitude and overtraining could also decrease the sea level VO2 max.

Acid/ base changes and buffering

The PCO2 in the blood is decreased by the hyperventilation, and therefore a decrease in hydrogen ion level occurred and an increase in PH level resulted. The respiratory alkalosis increases the renal bicarbonate excretion in the kidney. This stimulates the respiratory centre and ventilation is further improved. Blood bicarbonate is the primary buffer of lactic acid. The increase in PH cause the increase excretion of blood bicarbonate, and thus the ability of blood to buffer lactic acid will be decreased. Higher lactic acid level in athletes could be resulted from using more anaerobic energy, when aerobic energy is limited during early acclimatisation. However, a lower blood lactate concentration during maximal exercise has been showed after 6 weeks training at altitude than in sea level. A higher fat metabolism when compare to glycogen usage was observed during altitude training. Therefore, lower blood concentration of ammonia during exercise at altitude than at sea level was resulted. NH3 is suggested as a cause of fatigue and its concentration is reduced during short-term acclimatization to hypoxia. The often- described better feeling after altitude training might be based on this physiological effect.

The buffering in the body is less effective at altitude, due to loss of bicarbonate via kidneys as mentioned above. When the bicarbonate stores are replenished after descent, the increased haemoglobin mass and higher proportion of young red cell might raise the buffer capacity above pre-altitude values. An increased buffer capacity of blood against CO2 and lactic acid was found, after two weeks moderate altitude training. Study showed a small increase in nonbicarbonate can improve buffer capacity after altitude training, and that was correlated with improved endurance performance.

Muscle changes

In altitude training, a loss of body mass was a major concern. This is partly due to an increase in metabolic rate and a decrease muscle mass. Prolong exposure to altitude above 4500m has been shown to reduce muscle mass. The increase in metabolic rate can be controlled at altitude from 2000 to 3000m during training, because the energy intake can be regulated without too much difficulty. Muscle carbohydrate consumption is shifted from glycogen to blood glucose and lactate production decreased. De-acclimatisation of this lactate paradox last approximately 2-3 weeks. However, the importance for performance and measurement of anaerobic threshold after return to sea level remains unknown.

The assumption that hypoxia leads to augmented mitochondrial volume and oxidative enzyme capacity is not confirmed. Low-pressure chamber training resulted in an increased oxidative capacity and myoglobin concentration was reported, when compared to normoxia at equal training load. Enzymes of anaerobic metabolism are unaffected by altitude except under very severe hypoxic condition.

A positive correlation between relative increase in muscle buffer capacity and short term running at altitude was reported. There was a decrease in mitochondrial enzyme activity, and no change in VO2 max at sea level before and after altitude training. The authors suggested that hypoxia could be critical for enhancing muscle-buffering capacity, as a slower increase in O2 uptake has been observed under hypoxia when compared to normoxia. A greater O2 deficit and higher muscles lactate concentration were resulted, and these increase the anaerobic energy yield. If muscle-buffering capacity at sea level can be enhanced, athletes involved in anaerobic events may be benefit from altitude training.

Hormones are essential for metabolic regulation, but they are rarely investigated after the athletes had return to sea level. One study showed that plasma glucose, free fatty acid, lactate, cortisol and serum growth hormone concentration all increased during hypoxia exercise than with normoxic condition. It was suggested that these changes resulted in an increased mobilisation and utilisation of free fatty acid during exercise and a sparing of muscle glycogen. Besides, hormonal elevation may indicate overtraining. A significant increase in resting serum cortisol values has been found after altitude training in cross country and biathlon skiers that might indicate a subclinical overtraining state.

Aerobic power and endurance

Whether maximal aerobic power and endurance performance is enhanced after altitude is still controversial. Some studies showed that a decrease, no change or increase have been observed in VO2 max occurrence after altitude training. The comparison between studies is difficult as they use different training regime at different altitude. A decrease of 3.2% in VO2 max has been reported. While other study showed that significant improvement in aerobic performance after return to normoxia. Although there is no increase in VO2 max at sea level, 10 km personal best running time improved by 6% has been shown.

Submaximal percentage of VO2 max has been showed to be highly correlated with endurance performance. Altitude training has shown to improve endurance performance although VO2 max was unchanged. A possible explanation is the hypoxia environment decreased oxygen supply and reduced the aerobic capacity. Therefore, sympathetic stimulation occurs and this is similar to the situation in endurance sports. The increase in endurance time found with altitude acclimatisation may be due to a decreased reliance on glycogen and an increased use of fat stores as mentioned above, or an increased ability to tolerate decreased PH.

Practical implications

There are several potential problems related to altitude training. Preliminary evidence showed that additive stress of hypobaric hypoxia might provoke an adverse immune response. This would present a threat to both the fitness and health of the elite competitor. Besides, careful monitoring is needed to avoid overtraining at altitude. A significant increase in resting serum cortisol has been found in national Finnish cross-country skier after altitude training. This suggested altitude may impose a stress on athlete to exhaustion and a negative response is resulted. Stress hormone may have negative effect on the erythropoiesis in the bone marrow

In addition, iron loss is another problem need to be solved when adopted altitude training. When a sea resident exposure to high altitude, iron absorption elevated by 3.8 times and the clearance of iron from the plasma increase by 35% (4500m above sea level). This explains polycytemia occurring at a high altitude exposure, the great demand of iron to synthesis haemoglobin. Hypoxia increase iron demand and mobilisation, and therefore endurance athletes training at altitude may be prone to iron deficiency. This may be the explanation of some studies that failed to show an increase in Hb concentration, as only a suboptimal iron stores was reached on pre-altitude training. As a result, several authors suggested iron supplement is essential before and during altitude training. Besides, air is drier and hyperventilation occurred in higher altitude, constant fluid loss is encountered in the respiratory system. Therefore, water consumption has to increase at high altitude.

Based on the anecdotal date collected on a retrospective study, altitude training may be suitable for experienced athletes for several conditions:

  1. aerobic boost prior to high intensity training in preseason
  2. performance advantage in endurance events at sea level
  3. aerobic fitness during and post injury
  4. preparation for quicker recovery between rounds of competition and
  5. preparation for performance at altitude.

Duration and elevation of exposure

For the level of training, an altitude between 2200 to 3500m was recommended because training intensity is not scarified. Red blood cell mass does not increase until PO2 decrease to 65mmHg. This is corresponding to altitude level around 2200m. Athlete might suffer from altitude sickness above 3500m, and the large decrease in VO2 max will affect the intensity of training for maintaining aerobic fitness.

Several authors support the recommendation of level of altitude mentioned. Study showed that a biphasic relationship exist between the arterial partial pressure of oxygen and red blood cell mass. A clear inflection point at a critical PO2 of 67mmHg was also showed, that is equivalent to an interpolated arterial oxygen saturation of 92%. This point is correlated to the steeper portion f the oxygen-Hb dissociation curve. The equivalent PO2 would equate to about 135mmHg and is comparable with an altitude of 2200-2500m above sea level. That is required to stimulate sufficient hemopoiesis at rest to influence endurance performance. Negative effects from reduced caloric intake and sleep disturbances should be avoid in altitude. To avoid these drawbacks and maintain the exercise intensity at a sufficient level, training at about 2000m is suggested.

The anecdotal data collected by suggested that each raining camp should be last for 3 weeks in duration and twice a year. This allows time for physiological response to occur and gain performance advantage. The first altitude training should be held in preseason and the second prior to major competition. At least 7 week between the two session of altitude training is recommended.

Different combinations of living and training

Living high training low (LHTL) has been introduced into altitude training. Living high theoretically provides the advantages of adaptation to altitude and the undisturbed training intensity at sea level. With this programme, the disadvantage of training at high altitude: hypoxia, different temperature, inconvenient training condition and additional emotional stress that lead to reduction of maximal oxygen uptake and working muscles mass could be reduced.

One study conducted that recruited nine competitive runner for a 4-week experimental training period. A low-low group lived and trained at 1300m while a high-low group lived at 2500m and trained at 1300m with the low-low group. A significant improved (5%) maximal oxygen uptake was gained in the high-low group only. The high-low group also improved their sea level 5 km running time by 30 seconds. Besides, there is a significant increase in total blood volume of 500 ml in high-low group but not in low-low group. This suggested that acclimatization might be the most important factor for improving exercise performance at sea level. In addition, the training at lower level avoided problems related to decrease training pace usually seen at higher altitude. Another researcher has conducted a study using 3 altitude houses to investigate the living high training low approach. The altitude house consists of a nitrogen membrane generator to monitor the oxygen level at the predetermined limit. Elite skier lived and slept 14 to18 hours daily in the altitude house, where the oxygen concentration (PO2=116mmHg) was kept at a level corresponding to 2500m. The athletes performed normal training at sea level 1 to3 times a day. The result showed that serum erythropoietin and reticulocyte numbers were both significantly increased during the 8-day altitude house exposure period. Heat rate and blood lactate levels were tested during a treadmill test in the house and result showed that this parameter behaved exactly the same as in normal altitude training. They concluded that altitude house can be used to simulate moderate altitude living atmosphere at sea level to enhance sea level performance in elite athletes. Another study showed that ten days of living high (2200m) and training low resulted in greater improvement in 400m running. Both running time and velocity at a fixed concentration of blood lactate was improved when compare with equivalent programme at sea level training.

In return to sea level

Whether altitude training can improve performance depends on the physiological response in return to sea level. On descent, time is needed for maximise performance. Maximal performance has been reported after 15 to 28 days when return to sea level. Poor performance is usually seen from day1-11, followed by normal performance from day 8-17 and maximal performance 15-28. However, some authors concluded this varies between individual athletes. One study showed that there is a progressive decrease in erythrocyte production and iron stores reach a minimum level after 2 to 3 weeks when return to sea level. These may account for deterioration of red cell mass and haemoglobin level weeks after altitude training. Therefore, the period of altitude training should be carefully considered with respect to the competition season, so that sufficient time is allowed for maximise the training effects.

Conclusion

In conclusion, a number of persistence physiological changes after an altitude stay should actually contribute to improvement in endurance capacity (especially trained respiratory muscle, increased alveolar PO2, increase blood volume, reduce red cell age, decrease lactate and ammonia concentration, increase buffer capacity). Recently approach of living high and training low has showed to enhanced endurance performance. In addition, maximal oxygen uptake mostly measured may be less sensitive for monitoring performance capacity changes. The endurance time measurement is suggested to show the effect gained in some studies. Therefore, further research may be needed to review the benefit of altitude training using measurements other than VO2 max, and the potential benefits of altitude training for power athletes.

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Exercise Physiology Educational Resources 2000