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Does Altitude Training Improve Sea Level Performance In Endurance Athletes?

Proposition for Debate - by Nicola Brash

Statement of the Topic
Introduction
Background Knowledge - The Challenge of Altitude
New Knowledge
Conclusion
References
Short Answer Review Questions

Statement of the Topic

Does altitude training improve sea level performance in endurance athletes?

Introduction

Altitude training prior to competition at sea level has been used by elite athletes since approximately 1968 (Peronnet 1994). While it is well established that adequate acclimatization and physical training at altitude improves performance at altitude, it is questionable whether training at altitude also improves performance at sea level, more than training at sea level itself.

The use of altitude training to optimally enhance sea level endurance performance is widely practiced by athletes and coaches who primarily believe that acclimatization to environmental hypoxia initiates a series of metabolic, muscular and cardio-respiratory adaptations that will influence oxygen transport and utilization.

Additional beliefs for training at altitude include; improvement in coordination and reaction times, aerobic fitness during and post injury, a more rapid recovery between rounds of competition and between rounds at sea level, and for an aerobic boost prior to high intensity training.

Variables thought to influence the physiological outcomes of altitude training are: the level of ascent, the duration of time spent at altitude, the athletes pre-altitude level of fitness, intensity and type of training performed at altitude, and it appears most importantly, the variation in an individuals response to acclimatization and altitude training. The consensus of opinion amongst experienced coaches is that the optimal benefits of altitude are achieved by training at a moderate altitude of 2000-2500m for a duration of three weeks, and that peak performance on return to sea level occurs during days 15-28. However, scientific evidence to support the use of this strategy for improving sea level performance is scarce. The best designed studies on living and training at altitude as recommended above, show no benefit for sea level endurance athletes. Despite this knowledge, elite athletes continue to spend valuable time and resources living and training at altitude to optimize sea level performances. However, in 1991 a new training strategy was introduced to gain an advantage in sea level performance over just sea level training alone. Instead of living and training with constant altitude exposure, athletes began to live at altitude while continuing to train at sea level ("live high, train low"). This approach is hypothesized to optimize the benefits of acclimatization while maintaining training intensity thus, leading to enhanced sea level performances.

Background Knowledge - The Challenge of Altitude

Air density decreases progressively with ascent above sea level. However, the amount of oxygen contained in the air at altitude does not change i.e. both sea level and altitude O2, is equal to 20.93 percent. It is the density of oxygen molecules in the air (P_O₂) that is reduced in direct proportion to the fall in barometric pressure upon ascending to higher elevations. Therefore a decrease in oxygen availability occurs as one ascends in altitude.

McArdle et al (1996, p. 483) state "The challenge of altitude is directly from the decreased ambient P_O₂ and not the reduced total barometric pressure per se or from any change in the relative concentrations of the gases in the inspired air."

Because the diffusion of oxygen across the alveoli is directly dependent on the P_O₂ gradient, a decreased P_O₂ results in less oxygen transfer from the air into the blood and thus, to the tissues of the body. The body responds to this exposure to hypoxia via physiological adaptations that aim to facilitate oxygen transport and therefore, maintain tissue P_O₂ and oxygen consumption (V_O₂). This adaptive response is termed acclimatization. Each adjustment to a higher altitude is progressive and requires time (Boning 1997).

Within the first few hours of altitude exposure hyperventilation occurs to counter the decrease in availability of O₂. The increased respiratory rate also causes an increase in CO₂ excretion via the lungs. This leads to a decrease in PaCO₂ and subsequently hydrogen ion levels, resulting in a rise in blood PH.

The cardiovascular system initially responds to hypoxia by increasing both heart rate and cardiac output. It is reported that the submaximal heart rate and cardiac output can increase up to 50 percent, while stroke level remains unchanged. These adaptations increase the rate of blood flow therefore, partially compensating for the decrease in O2 in arterial blood (McArdle et al 1996).

Before reviewing the results of different altitude training strategies, it is important to briefly describe some of the longer-term physiological changes that occur in response to altitude that could benefit exercise performance at sea level.

Physical training at altitude is thought to invoke similar physiological changes to those caused by endurance training at sea level. The adaptations considered most important for performance enhancement include increases in blood haemoglobin and myoglobin, improved buffering capacity and improved aerobic enzymes in the muscles.

It is postulated that the stress of hypoxic exposure, in addition to training stress will compound the training adaptations the athlete experiences and therefore be an advantage over sea level training (Wolski et al 1996).

Haematological Adaptations

The most sought after physical adaptation at altitude by scientists, athletes and coaches is an increased efficiency of oxygen transport and consumption and thus, an increase in work capacity (Boning 1997). The mechanism thought to be responsible is an increase in red blood cell mass. This is expected to lead to an improved Vo2max and thus, sea level performance (Rusko 1996). Hypoxia is thought to stimulate the production of red blood cells (erythropoiesis), which will lead to an increase in total red blood cells (polycythemia). Polycythemia directly translates into an increase in the blood's capacity to transport oxygen (McArdle, Katch and Katch 1996).

Debate exists in the literature as to whether a true increase in red blood cell mass occurs or if the increased oxygen content of arterial blood is solely due to hemoconcentration, which occurs as a response to a rapid decrease of plasma volume after arrival at altitude.

Plasma volume is thought to decrease within the first 2-3 days of altitude exposure due to a fluid shift from the intravascular space into the interstitual and intracellular spaces. The reason for this shift in fluid balance appears to be related to a decrease in antidiuretic hormones, the dry enviroment and hyperventilation (Berglund 1992).

Fulco et al (2000) states that after 2-3 weeks at altitude arterial oxygen content is restored to near sea level values due to a decrease in plasma volume with little change in red blood cell number and an increase in arterial oxygen saturation due to ventilatory acclimatization, but cardiac output is reduced. Therefore, during maximal levels of exercise the potential advantage of a restored arterial oxygen content is cancelled out by the reduction in cardiac output. Additionally, Vo2max remains depressed after 2-3 weeks of altitude acclimatization compared with sea level.

However, other studies suggest that there is a true increase in red blood cell mass. These studies have demonstrated an increase in erythrocyte production beginning within 4-7 days of altitude exposure. It is postulated that there is a one percent increment per week in the true haemoglobin level during hypoxic exposure. As there is a 12 percent difference in haemoglobin levels between sea level residents and those who reside long term at altitude, an inference can be made that it would require a minimum of 12 weeks altitude exposure to achieve the optimal level of acclimatization (Bailey and Davies 1997, Berglund 1992, Wolski et al 1996). Furthermore, there is a critical value of PaO2 for red cell mass production. It has been shown that red cell mass does not increase until PaO2 decreases below approximately 65 mmHg, this tends to occur in most people at altitudes between 2200-2500m. Therefore it is unlikely for physiological adaptations to take place at altitudes below this value (Levine and Stray-Gundersen 1992).

Another important consideration is the availability of iron in the blood, which is crucial for the production of blood cells and platelets in the bone marrow (haemopoiesis). It appears that low iron stores may significantly limit any potential benefits from training at altitude. Berglund (1992) suggests that when exposed to altitude, sea level residents experience an increase in iron absorption of approximately 3.8 times, and the clearance of iron from the plasma also increased by 35 percent. To overcome this effect the author recommends starting iron supplementation 2-3 weeks prior to commencing altitude training, then continue through the first 2-4 weeks at altitude. However, a study by Friedmann et al (1999) concluded that iron supplementation in non-iron-deficient athletes cannot be recommended during endurnce training at moderate altitude as it was found to be detrimental to their subjects total body haemoglobin (TBH) levels, for reasons that could not be explained from their research.

It is also worth mentioning here that an increase in the blood's oxygen carrying-capacity also occurs at sea level with endurance training, as this is the body's normal response to physical activity. For instance, at sea level endurance athletes with a high aerobic capacity can achieve a haemoglobin concentration (Hb) measuring twice that of sedentary controls. Additionally, plasma volume increases by as much as 500ml after approximately one month of endurance training at sea level. This is due to the increased activity of the renin-angio-tensin-aldosterone (RAA) system, which is stimulated during exercise (Berglund 1992).

Lactic Acid Buffering Capacity

It has been demonstrated that during submaximal exercise there is a decrease in blood lactate levels in acclimatized athletes at altitude in comparison to sea level, at the same absolute exercise intensity. This could be due to increased lactate removal from the blood and/or in response to altitude, the muscles use less glycogen as the main source of energy leading to a decreased production of lactate. This adaptation is termed the lactate paradox as it is expected that a state of hypoxemia would increase lactate accumulation, in fact the opposite occurs. Additionally this reduced lactate concentration during altitude hypoxia is not associated with an increased V_O₂max or enhanced oxygen delivery to the tissues post acclimatization (Boning 1997, McArdle et al 1996).

Furthermore, McArdle et al (1996, p.491) states: "Reduced blood lactate accumulations at high altitude do not appear to be due to the decrease in buffering capacity that accompanies high-altitude acclimatization".

Blood bicarbonate is the primary buffer of lactic acid. Hyperventilation reduces arterial CO₂ resulting in an elevated PH level. To compensate the kidneys excrete more bicarbonate, this in turn reduces the effectiveness of the body's buffering capabilities. However an increase of red blood cell mass including numerous young red cells is postulated to raise the buffer capacity against lactic acid and CO₂, above pre-altitude levels when these bicarbonate stores are replaced upon return to sea level (Boning 1997).

Wolski et al (1996) suggests that if muscle buffering capacity at sea level can be enhanced by altitude acclimatization, then altitude training may also be an advantage for athletes competing in anaerobic sporting events.

Muscular Adaptations

Post acclimatization, muscle biopsies from humans residing at altitude are found to have a myoglobin level up to 16 percent higher than at sea level, as well as a significantly increased number of mitochondria and enzymes required for aerobic energy transfer.

Studies investigating muscular metabolism report an increased concentration of 2,3-diphosphoglycerate 2,3-DPG). This compound is produced in the red blood cell during the anaerobic reactions of glycolysis. 2,3-DPG reduces the haemoglobin molecules affinity for oxygen and therefore may reflect an adaptive response to facilitate oxygen delivery to the tissues during strenuous exercise (McArdle et al 1996, Rusko 1996).

It is also theorized that altitude might increase the concentration of skeletal muscle capillaries that would reduce the distance for oxygen diffusion between the blood and tissues. Such adaptations could lead to an increase in the oxygen reservoir within muscle fibres and improve oxidative function (McArdle et al 1996). Therefore the increases in haematocrit, haemoglobin, aerobic enzymes, muscle myoglobin level and muscle buffering capacity are important training adaptations that may be augmented by training at altitude. However, the significant reduction in plasma volume, total blood volume and VO2max with altitude exposure may negate the potential physiological benefits.

Exercise Training and Residing at Altitude.

Well designed studies with appropriate control groups found that altitude training is not superior to equivalent training at sea level for enhancing either altitude or sea level performance. This indicates that the adaptations of training per-sé exceed any additional benefit gained by altitude training (Levine and Stray-Gundersen 1992)

However Fulco et al (2000) suggests that moderate altitude training can provide an additive effect on subsequent sea level performance of highly conditioned athletes. These studies found that matched training programs performed by athletes with already high fitness levels, at both sea level and altitude, found no improvement in Vo2max after sea level training but a significant increase in V_O₂max after altitude training. This may or may not provide these athletes with the edge they require to win their competition.

Another topic of debate is whether Vo2max is a reliable and valid measure of physical performance. Many studies report that altitude exposure had no effect if V_O₂max did not improve, however Fulco et al (2000) states that this interpretation may be incorrect as significant improvements have been shown to occur in response to standard endurance tests and during athletic performances with or without an increase in V_O₂max.

In the past the relatively small number of well controlled studies on living and training at altitude have clearly demonstrated no benefit in sea level performance. This conclusion is contrary to what we would expect from the physiological adaptations that occur during altitude training therefore, recent studies have begun to consider more closely the potential confounding variables i.e., negative effects of altitude training, that may negate the positive adaptations to acclimatization and thus, veil any improvements in sea level performance.

Negative effects on performance in response to altitude training.

Induced hypoxia results in a decrease in maximal aerobic power of approximately one percent for every 100m above 1500m. (Levine and Stray-Gundersen 1992). As Vo2max declines with increasing elevation (Terrados 1992), the specific power output will correspond to a higher relative exercise intensity, i.e. a higher percentage of Vo2max. This leads to higher blood lactate levels, elevated heart rate, increased ventilation and increased perceived effort. Therefore, an inference can be made that training at altitude compared to sea level leads to a decrease in power output, and a relative deconditioning could potentially occur (Fulco et al 2000). Therefore highly conditioned athletes may not be able to sustain the same level of training intensity they can achieve at sea level, which may negate the positive effects of altitude that might have lead to an improvement in sea level performance.

Another factor which could lead to a decrease in sea level VO2max, after altitude training is overtraining. Rusko (1996) found a significant rise in resting cortisol levels in their national team of cross-country and biathlon skiers, after altitude training. They postulated from this that training at altitude may be so physically stressful that the athletes become exhausted and therefore unable to react positively to the altitude training stimulus.

A study by Boning (1997) also demonstrated an elevated resting cortisol concentration in their subjects after descent which adds weight to Rusko's (1996) theory above that, altitude training may induce a subclinical overtraining state.

Liu et al (1998) cites numerous studies that demonstrate additional negative effects of training at altitude. These include a reduction in working muscle mass, decreased maximal oxygen uptake, an impairment of gas exchange, and reduced stroke volume. However, Terrados (1992) states that the reduction in muscle mass due to an increased metabolic rate can be avoided if athletes do not train above 3000m.

In an attempt to avoid these adverse responses to hypoxic training, while capitalizing on the beneficial effects of altitude exposure, a new approach has been introduced by Levine and coworkers in 1991, where the athletes live at altitude but train at sea level, the coined term is living high, training low (LHTL).

New Knowledge

A Case For Training at Sea Level While Residing at Moderate Altitude.

The proposed physiological benefits of altitude training may be due to the effect of acclimatization, an enhancement of the training effect by hypoxic exercise or both.

In the past it has been difficult to interpret from studies, which provides the most effective stimulus for enhancing exercise performance.

In order to examine the effects of hypoxic exercise training without acclimatization, recent studies had subjects train in hypobaric chambers while continuing to live at sea level, while other studies had altitude natives train at altitude to reduce the confounding variables caused by the progressive physiological changes associated with altitude acclimatization. These authors showed no significant changes in Vo2max, haemoglobin level or haematocrit. Therefore, no additional benefit appeared to be gained from training at altitude over the physiological benefits achieved by previous acclimatization. (Fulco et al 2000, Wolski et al 1996)

Levine et al (1990) cited in Wolski et al (1996) successfully designed a study that separates the effects of acclimatization and altitude training. In this study they had one group live at altitude and train at sea level, and another control group both live and train at sea level. Their results demonstrated that the athletes whom were living high and training low improved their Vo2max by 5 percent and most importantly, decreased their 5000m run time by 30 seconds, compared with the athletes who lived and trained at sea level. From this study the authors concluded that it is the acclimatization rather than the altitude training per se that improves sea level performance.

This conclusion lends weight to the efficacy of living high and training low (LHTL) by demonstrating that training in hypoxic conditions may not be important for improving sea level performances. Therefore it may be possible to avoid the detrimental effects shown to occur with training at altitude without losing any of the benefits obtained by acclimatization, which is postulated to be the most effective stimulus for altering exercise performance.

Due to the fact that cardiac function is one of the major determinants of oxygen delivery, a study by Liu et al (1998) investigated the effect of LHTL on the resting cardiac functions at sea level in athletes. They found no significant change to the cardiac function of already well trained athletes, but mentioned that they found evidence to suggest that LHTL may improve systolic cardiac function and left ventricular contractility. What was unanswered by this study is, do these potentially beneficial effects of LHTL on cardiac function correspond to any measurable improvement in physical performance at sea level?

Research by Stray-Gundersen et al (1999) also confirms that LHTL can improve sea level endurance performance in already well-trained competitive runners, above and beyond equivalent sea level training. This series of well designed studies were randomized, had an adequate number of subjects in each group, used highly motivated and trained athletes who were accustomed to intense training, used appropriate control groups, documented what the training sessions involved in detail, and measured exercise performance in a variety of different ways (Fulco et al, 2000). These authors hypothesized that if an athlete lives at the correct altitude for the correct time period i.e., four weeks in their studies, they will increase their red cell mass. If at the same time they are able to maintain their current training velocity and oxygen flux i.e., by continued training at sea level, they should show improvement in their sea level performance as a direct consequence. This series of well-controlled and designed studies showed a 1.4 percent improvement in performance, immediately on return to sea level and for up to three weeks after. Whether 1.4 percent in real terms, is associated with a measurable advantage in performance for an athlete, is questionable. However to place it in perspective these authors stated that the LHTL athlete would be at the finish line and the living high, training high (HiHi) and living low, training low (LoLo) control groups would still have approximately 100m to run. The same authors also found that the LHTL athletes obtained a significant 500ml increase in blood volume that was not seen in their control groups, thus providing further evidence that acclimatization may be the most important factor in improving sea level performance with altitude training. Another recent study by Nummela et al (1996) has confirmed this LHTL hypothesis for maximizing sea level performance in 400m race times as well as anaerobic running tests. In Finland, Rusko (1996) investigated the LHTL approach by using altitude houses where the athletes could live in pre-set hypoxic conditions and go outside 1-3 times per day to train at sea level. The results confirmed an increase in serum EPO, reticulocyte number, and 2,3 diphosphoglycerate. These physiological adaptations remained elevated for at least two weeks during the altitude house exposure. However, whether these specific physiological changes would correspond with an improved sea level performance in these subjects was not discussed.

A potential drawback to LHTL is that there may be medical problems associated with the athletes having to alternate between sea level and altitude on a daily basis. It is recommended that further research be done to determine if this method is safe for the athletes (Wolski et al 1996). Additional important questions that have not been addressed in the LHTL studies reviewed are: How long do these beneficial effects last after cessation of LHTL? Does this response vary widely between individuals, as demonstrated in the studies for living and training at altitude? What altitude and time period of LHTL maximizes these beneficial physiological adaptations?

Conclusion

Residing at altitude allows a number of potentially beneficial physiological, ventilatory, haematological and metabolic adaptations to occur. These adaptations are postulated to improve endurance exercise performance. While is widely supported that training at altitude enhances performance at altitude, there is much less support for the view that altitude training will improve sea level endurance performance.

It is now theorized that the reason that many studies found no improvement in sea level performance after altitude training is due to the fact relative deconditioning appears to occur while training at altitude, which may offset the potential beneficial changes resulting from altitude exposure.

Therefore a new strategy has been introduced where the athletes live at altitude but train at sea level. This approach allows both the beneficial adaptations of acclimatization to develop, as well as provide the opportunity to train without reducing power output during exercise. Therefore, this strategy is accumulating support from scientists, athletes, and coaches alike, as the most advantageous method for enhancing sea level performance in highly trained endurance athletes.

In conclusion, well trained athletes whose development has included adequate base preparation with regular, high intensity interval work, and have reached a plateau in their training response at sea level are likely to derive the most benefit from altitude training using the LHTL approach.

References

Bailey D and Davis B (1997): Physiological implications of altitude training for endurance performance at sea level: a review. British Journal of Sports Medicine 31:183-190.
Berglund B (1992): High-altitude training: aspects of haematological adaptation. Sports Medicine 14:289-303.
Boning D (1997): Altitude and hypoxia training. International Journal of Sports Medicine 18:565-570.
Friedmann B, Jost J, Rating T, Weller E, Werle E, Eckardt K, Bartsch P and Mairbaurl H (1999): Effects of iron supplementation on total body hemoglobin during endurance training at moderate altitude. International Journal of Sports Medicine 20:78-85.
Fulco C, Rock P and Cymerman A (2000): Improving athletic performance: is altitude residence or altitude training helpful? Aviation Space and Enviromental Medicine 71:162-171.
Levine B and Stray-Gundersen J (1992): A practical approach to altitude training: where to live and train for optimal performance enhancement. International Journal of Sports Medicine 13:209-212.
Liu Y, Steinacker M, Dehnert C, Menold E, Baur S, Lormes W and Lehmann M (1998):: Effect of "living high-training low" on cardiac functions at sea level. International Journal of Sports Medicine 19:380-384.
McArdle W, Katch F and Katch V (1996): Exercise Physiology. (4^th ed). Baltimore: Williams & Wilkins.
Nummela A, Jouste P and Rusko H (1996): Effect of living high and training low on sea level anaerobic performance in runners. [Abstract] Medicine of Science and Spots Exercise 28:S124.
Peronnet F (1994): Altitude training did not speed up the progression of running performance in man. International Journal of Sports Medicine 15:335-336.
Rusko H (1996): New aspects of altitude training. The American Journal of Sports Medicine 24:48-52.
Terrados N (1992): Altitude training and muscular metabolism. International Journal of Sports Medicine 13:206-209.
Wolski L, McKenzie D and Wenger H (1996): Altitude training for improvement in sea level performance: Is there scientific evidence of benefit? Sports Medicine 22:251-163.

Short Answer Review Questions

Why does training at altitude result in relative deconditioning of athletes?
What physiological adaptations occur in response to acclimatization?
Why are these adaptations beneficial to endurance athletes?
Why have studies in the past shown no benefit from altitude training on sea level performance?
What is now proposed to be the best approach to altitude training for improving sea level performances? Why?

Exercise Physiology Educational Resources 2000