ELITE SWIMMERS AND ALTITUDE TRAINING
Human acclimatization to passive stresses serves as the basis for understanding physiological responses to altitude exposure. Published research pertaining to swimming and endurance training is reviewed. It is argued that altitude training does not facilitate improved performances at sea-level because of the specificity of the acclimatization response. It is argued that if complete altitude acclimatization was to occur, it would not be possible to train with sufficient volume or intensity to maintain high levels of performance. Although the field contains many studies, those which are definitive lead to the conclusion that altitude training is not an avenue for enhancing the sea-level performances of highly-trained swimmers. The practice of conducting altitude training camps for elite swimmers is not justified on either physiological grounds or performance benefits.
This article analyzes the proposal that altitude training benefits sea-level performances in trained elite swimmers. It explains some important concepts, evaluates research weaknesses in the field, and attempts to establish a definitive position on the topic.
The status of opinions about the effectiveness of altitude training on sea-level performances of highly-trained athletes is one of division. Noted authorities in applied exercise physiology currently accept that there is insufficient evidence to support any beneficial effect (Brooks & Fahey, 1984, p. 495; McArdle, Katch, & Katch, 1991, p. 543; Noble, 1986, p. 439; Rushall & Pyke, 1990, p. 137; Sutton, 1994, p. 12). Well-formed studies have not found such an effect. Wilmore and Costill (1994) specifically questioned the wisdom of altitude training for swimmers. For running events, it has even been proposed that since the increase in popularity of altitude training the rate of progress of world-records and best times has slowed (Peronnet, 1995).
Many coaches, and some sport "scientists," advocate the value of altitude training despite a lack of acceptable objective evidence. Advocates steadfastly hold to their opinions. For example, at a meeting of the Sports Science Committee of Australian Swimming Inc., an evaluation was made of the effect of its altitude camp, held prior to the 1995 Pan Pacific Championships, on the performances of Australian Team swimmers. Statistical analyses showed no significant benefits from the experience (Australian Swimming Inc., 1995). Although the discussion group was largely supportive of the altitude training concept, swimmer's performances did not reveal objective conclusions other than no effect. Despite this, there still were persistent attempts to imply some benefits from the experience. Further considerations of altitude training for prospective Olympic level athletes were entertained by the US Swimming Steering Committee. The concepts considered were based on opinions, several of which could be argued as being confused and erroneous, and contained the recommendation that ". . 90% of our athletes really should do this altitude training somewhere prior to the anaerobic load to enhance the process of anaerobic training to facilitate recovery to enhance the aerobic system" (Pursley, 1995, p. 5).
Personal opinions are common amongst altitude training proponents. In the confounded circumstances of national team training camps, explanations for improvements, other than an altitude effect, are uncommon (Pursley, 1995). The resiliency of coaches and advocates has been supported partly by some questionable articles and writings that have found their way into the literature. Unless studies are analyzed carefully for various aspects of experimental control, false conclusions from "published" research can be drawn.
Scientific investigations report two classes of response to altitude: (a) physiological mechanisms (e.g., VO2max, hemoglobin (Hb) concentrations), and (b) performance levels (e.g., time to run a particular distance). Although physiological and performance changes normally occur in concert with exercise stimulation, it does not necessarily follow that physiological changes from a non-exercise stimulus (i.e., altitude) will promote exercise performance changes in an unrelated environment (i.e., sea-level) (Wolski, McKenzie, & Wenger, 1996). This latter concept of transfer of effects seems to underlie many proposals concerning altitude training.
There is a strong possibility that altitude training can assist throwers, jumpers, and sprinters (Karvonen, Petola, & Saarela, 1996). The diminished air-resistance and gravitational pull allows performance magnitudes to be practiced that are not possible at sea-level, resulting in mechanical gains which possibly exceed the body's performance decrements. However, the mechanical environment of swimming is practically constant. Changes in sprinting performance after training at altitude have been reported (Martnio, Myers, & Bishop, 1995) but in a study where the use of a control group was questionable. This paper's considerations are generally limited to swimming and endurance activities because of similarities in physiological responses to exercise. The inclusion of endurance activities such as running and cycling is meant to partly offset the sparse literature on swimming at altitude.
This presentation is concerned mainly with aerobic endurance adaptation. It is appropriate for all swimmers because: (a) events of 200 m or more are primarily aerobic, (b) even 100 m sprint events have a considerable aerobic component, and (c) all swimmers participate in a very large amount of aerobic work at practice (Troup, 1990). Aerobic responses also have been the focus of a major portion of relevant research.
For this review high altitudes are considered to be in excess of 3,000 m while moderate altitudes range from 1,800 to 3,000 m. One should not assume the magnitude and timing of adaptations to high altitude exposure would be the same as those at moderate altitude. The majority of references are those which should be readily accessible and understandable by a discerning practitioner. In those references, the basic research to support assertions is usually included.
To better understand the mechanisms and dispositions of humans when reacting to altitude it is worthwhile to consider some general principles of human acclimatization and adaptation. The general characteristics of adaptive responses have been known for quite some time (Selye, 1950). Acclimatization is appropriate for a relatively short period of exposure, such as when swimmers are taken to an "altitude" camp for a month. Adaptation refers mainly to changes that occur over generations under constant exposure to a stress. Many of the features of acclimatization and adaptation are similar and in this paper there will be no distinction drawn between the two.
When individuals habitually live at sea-level, their energy and muscular systems function optimally to accommodate existing atmospheric conditions. Climate moderates that functioning. In hot-humid environments, the adaptations are different to those of dry-cool climates. The flexibility of responses of the human body to various combinations of altitude and climates has made it possible for humans to populate many parts of the earth.
Generally, the body acclimatizes in a variety of ways depending upon the environmental stresses to which it is exposed. Passive stresses are those which are persistent and relatively invariant (e.g., altitude, climate) and active stresses are those which are occasional/variable (e.g., exercise, emotions, diet, vocations). Reactions to excessive stresses are modified by the individual attributes of each person and the nature of the stress. Anholm et al. (1996) reported an example of acclimatization specificity. "Cardiovascular drift" can be observed in extended endurance exercise but at altitude, this feature is manifested differently to that of sea-level. The adaptations and acclimatizations to passive environmental stresses are specific and generalize little between environments (Fox, Bowers, & Foss, 1993).
As an example of the specific demands of active stresses, it has long been recognized that in serious athletes oxygen transport enhancements developed in one form of exercise rarely, and if then only marginally, influence similar characteristics in other activities. For example, VO2max improvements in cycling do not show any substantial changes in VO2max of running (Pechar, McArdle, Katch, Magel, & DeLuca, 1974). Similarly, VO2max improvements in swimming do not influence any change in VO2max of running (Rushall & Pyke, 1990). It should be noted though, that VO2max improvements in running do "transfer" some very minor effects to more specific activities, such as swimming, kayaking, and cycling, in moderately-trained persons. However, with elite athletes, training effects are so specific that there is little to no beneficial carry-over of circulatory improvements from one activity to another. Passive and active stresses interact when training at altitude. Beneficial sea-level performance enhancements from that interaction have to be substantiated.
The length of exposure to passive stresses modifies the nature of changes and the resiliency of those changes when the stress is removed. When a person is exposed to moderate altitude, some initial responses occur to accommodate the changed conditions and in time others follow (Smith & Sharkey, 1984). As the duration of the exposure increases, the repertoire of acclimatization changes becomes complete. The greater the length of time that the body is in a fully acclimatized condition, the more habitual become the changes. Thus, upon exposure to a passive stress, the body undergoes a hierarchy of responsive changes, and eventually becomes fully acclimatized to the point that the changes become constant as well as permanent while residing in the environment. This full acclimatization is compromised by shorter periods of exposure. Generally, the shorter the time spent at altitude, the less dramatic are the acclimatizations and those which do have an opportunity to occur are quite transient (Troup, 1990).
There are three main features that modify acclimatization responses.
If swimmers go to altitude "tired" and spend less than a month on a reduced workload and often with a simplified (less stressful) life-style, then an "unintentional taper" could occur. When those swimmers return to sea-level they may perform as well as or even slightly better than comparable sea-level swimmers, not because of beneficial altitude effects, but because they are more rested. This could be an explanation when sea-level improvements are found after altitude training. The same or a better effect might be achieved by staying at sea-level, reducing the strain of training, and/or simplifying swimmers' life-styles. These possibilities have yet to be investigated.
"The most important physiological adaptations to living at high [>3,000 m] altitude are increased ventilation of the lungs, increased blood hemoglobin, and enhanced extraction of oxygen by the tissues. Maximal cardiac output is not usually affected by altitude" (Sutton, 1994, p. 12). Several points can be made about this statement, while remembering that the acclimatizations discussed occur as a result of exposure to high altitude but are compromised at lower altitudes because varying degrees of stress invoke different levels of acclimatization (Faulkner et al., 1968; Smith & Sharkey, 1984).
To maximize oxygen transport at altitude, one needs to proportionally alter all links in the delivery, extraction, and utilization phases of the aerobic mechanism that results from the acclimatization process (Sutton, 1994). The elements of major change indicated above acclimate at different times (Smith & Sharkey, 1984). One can cautiously assume that the asynchronous development of the segments of the aerobic system will not accommodate the most effective acclimatization in the early stages. If the term of altitude residence is long enough, eventually all changes will be completed and maximal acclimated aerobic function will have occurred. Despite those changes, oxygen delivery at altitude will still be less than that of sea-level if aerobic fitness was fully trained prior to going to altitude (Sutton, 1994).
Maximum physiological capacities are not enhanced by altitude acclimatization. However, submaximal utilizations do change and are associated with improved altitude performance. The longer an athlete is exposed to altitude, the more performances at altitude improve, but they never reach the values obtained at sea-level (Fox et al., 1993).
Confusion in understanding physiological acclimatizations is often caused by the interaction of the acclimatization mechanisms with the altitude to which one is exposed. Since most swimmers are taken to altitude camps at a relatively low height (e.g., Colorado Springs is 1,860 m), the variations and compromises in the acclimatization processes usually will be noticeable between individuals. It is reasonable to expect at moderate to low altitudes that some athletes may not react at all while for others only some, and still for others all of the mechanisms of acclimatization may be exhibited.
There has been a suggestion that elite athletes are more sensitive to minor changes in altitude than non-elites and therefore, will exhibit fuller acclimatization characteristics a lower altitudes. Although only a few indicators of acclimatization were measured, Gore et al. (1995) recorded significant alterations in VO2max and arterial O2 saturation at a simulated altitude of 610 m. On the other hand, Rusko, Kirvesniemi, Paavolainen, Vahasoyrinki, and Kyro (1996), and Friedman, Jost, Rating, Mairbauri, and Bartsch (1996) recorded no changes in elite athletes (skiers and boxers respectively) at 1,800 m. Until Gore et al.'s work is independently replicated, its hypothesis that elite athlete will respond more notably than lesser athletes to moderate altitudes must be regarded cautiously.
Implications from Research
Acclimatization responses (increased ventilation, Hb, and O2 extraction) often are used as the theoretical justification for sea-level performance improvements. The reasoning is: improved oxygen transport factors at altitude must produce improved oxygen transport, and therefore physical performance, at sea-level (McArdle et al., 1991, p. 543). Yet only at altitudes in excess of 3,000 m do these changes normally occur fully and eventually in all humans (Sutton, 1994). At those altitudes it is not possible to perform the volume and intensity of beneficial high-level training that can be accomplished at sea-level. That produces a dilemma: is it better to have: (a) an altered physiology and less training volume and quality, or (b) full training without the altered physiology? The evidence suggests the latter. Since most "altitude" camps are conducted at low to moderate altitudes (e.g., in Australia they range from 1,600 to 2,000 m), acclimatization responses are not guaranteed to occur in their entirety or to their maximum level and will vary between individuals. Moderate to low altitude partial physiological acclimatization usually will not produce a physiological state that can be "theoretically" justified to improve sea-level performance (Sutton, 1984; Wolski et al., 1996).
Further problems arise with the concept of relatively brief exposures to moderate altitude training camps. If an athlete is responsive to the low hypoxic levels at such camps, considerable time will still be needed before all acclimatization responses can be completed. Trained runners took five weeks for performance and VO2max to acclimatize at 2,440 m (Sucec, Hodgon, Roy, & Hazard, 1996). A three-week training camp probably will produce observable, but partial, physiological changes but will require a period of disruption to normal training. Consistent training stimuli will not be maintained because of: (a) travel to the camp, (b) initial reactions to the new mild hypoxic stimulus which reduces the capacity to train, and/or (c) continued compromised training programs that do not support either or both the intensity or volume of work that could be sustained by elite athletes at sea-level.
It is popular in some countries to conduct several short-term training camps at altitude as part of an annual training plan. Support for benefits from such plans is not available in the form of objective evidence. Elite endurance skiers after training and racing at 1,600-1,800 m displayed an unchanged VO2max and reduced anaerobic power after a period from three to four weeks (Rusko et al., 1996). After three weeks at 1,800 m German National Team boxers failed to display any enhanced erythropoietic response (Friedman et al., 1996). For many swimmers altitude camps will amount to training interruptions accompanied by unrelated and partial stress acclimatizations which will be reversed upon return to sea-level. Despite what is known about acclimatization to training and altitude stresses, influential coaches persist with such experiences.
The increased use of anaerobic metabolism at altitude as a substitute for reduced aerobic function is evidenced by the body's alteration in fuel use. Altitude exposure increases the utilization of blood glucose at both rest and in exercise and active skeletal muscle is the predominant site of glucose disposal during high altitude (Brooks, Roberts, Butterfield, Wolfel, & Reeves, 1994a; Butterfield, Mazzeo, Reeves, Wolfel, & Brooks, 1996). Altitude acclimatization decreases reliance on free fatty acids as a fuel and increases the use of blood glucose in both rest and exercise (Brooks, Roberts, Butterfield, Wolfel, & Reeves, 1994b). These changes in fuel use indicate marked alterations in the metabolism underlying both exercise and recovery. It has marked implications for a particular emphasis on nutrition control at altitude training and competition sites.
It could be hypothesized that altitude training would benefit subsequent anaerobic sea-level performance since athletes withstand more discomfort than usual because of increased anaerobiosis at altitude (Daniels & Oldridge, 1970, p. 111). The greater utilization of the anaerobic energy system may be beneficial to sea-level anaerobic performances (Troup, 1992, p. 48). This is only speculation for it has not been investigated thoroughly. The major proportion of research has focused on aerobic benefits. Training and exercise at altitude requires the body to make up for the loss of aerobic energy capacity with anaerobic energy otherwise the work rate must be reduced to meet a diminished energy capacity. The extra stimulation of anaerobic mechanisms may be of benefit. Altitude training may allow a greater mobilization of anaerobic resources which may be difficult to achieve or is not possible at sea-level.
The effects of altitude training on anaerobic performance in swimmers was reported (Martino et al., 1995). Two groups trained under the same protocol. Swimming times and peak power improved significantly more for an altitude trained group than a sea-level group. Despite using a control group adequate controls for extraneous variables did not appear to be followed rendering these results suspicious. Further investigations are needed.
Disruption of neuromuscular patterns. The requirement for work at altitude to entail a greater amount of glycolytic activity is potentially harmful to performance of highly proficient athletes. A standard sea-level performance requires certain proportions of oxidative and glycolytic work. Those proportions are altered at altitude because of the inability to facilitate the same amount of oxidative work (Troup, 1990). Consequently, at altitude, a sea-level standard of performance is energized by altered proportions of the two energy components. To provide the greater amount of anaerobic work to offset the reduction in aerobic energy, glycolytic muscle fibers are recruited into the actions that support a particular level of performance (Brooks et al., 1994a). In highly skilled athletes where movement efficiency is a major requirement, the stimulation of altered muscular patterns at altitude could cause the efficiency of movement to be decreased. In sports where skill is a major determinant of competitive success this could be detrimental to performance.
Particularly in swimming, where high levels of performance are dependent upon swimming as fast as possible without stimulating glycolytic activity beyond the maximum lactate steady state, this altitude-stimulated change could be counter-productive to good training and performance efficiency at sea-level. This means that the economy of sea-level movement could be degraded by altitude acclimatizations, an effect observed by Daniels and Oldridge (1970) (sea-level running economy of world-class athletes was adversely affected after five weeks of intermittent altitude acclimatization). Troup (1990) reported improved swimming economies at sea-level following three weeks of altitude training but, on another occasion (Troup, 1992, p. 48) reported that altitude and sea-level trained groups did not differ in economy profiles or endurance capacities. It is possible that this factor requires a certain time period to become evident.
The main reason for lessened endurance performance at altitude is that it is a consequence of the lowered partial pressure of oxygen which results in varying degrees of hypoxia, the degrees being dependent upon the altitude.
On first arriving at altitude, trained subjects have no greater acclimatization advantage over untrained healthy individuals beyond that which existed at sea-level. Being fit does not alter the form or rate of acclimatization to altitude but does allow an individual to engage in exercise of greater intensity levels. Acclimatization rate depends upon the individual. There are some who never acclimatize and continue to suffer mountain or altitude sickness while at altitude (Fox et al., 1993).
The longer one remains at altitude, the more altitude performance improves. Most improvement occurs within the first two weeks but it never reaches the values that are obtained at sea-level. Sucec (1996) estimated the performance degradation of running events at the 1968 Olympic Games due to altitude. Event times were increased by the following amounts: 1,500 m (3.6%), 3,000 m (5.5%), 5,000 m (4.8%), 10,000 m (5.8%), and marathon (6.2%). He concluded that decrements in running event times due to an altitude effect are dependent upon the degree to which they rely upon aerobic energy. That performances never fully equate to sea-level standards suggests that altitude training fails to elicit specific neuromuscular patterning, exercise intensity, and psychological control factors, to transfer beneficially to sea-level competitive performances. For effective transfer of training effects to competitive performances to occur, the neuromuscular patterns, energy utilization proportions, and psychological experiences of the intended race have to be practiced. Altitude training does not allow the first two of those features to be practiced.
Problems With Past Research
In many studies which show improved sea-level performances after altitude training, possible confounding variables have not been controlled. For example, in some investigations it was not determined whether improved performances were due to altitude exposure or to the fact that subjects eventually increased their fitness level during altitude conditioning. In such cases, it is likely performances would have been improved with further training had the subjects remained at sea-level. Many studies lack adequate control of all factors other than altitude acclimatization.
"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" (Smith & Sharkey, 1984, p. 54).
It is possible to derive a good control group that is matched on critical potentially confounding variables. For example, 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 training was found (Adams, Bernauer, Dill, & Bomar, 1995).
Another very common research weakness is to use one or, at most, a very few limited indices of acclimatization. Because VO2max changed at or after returning from altitude does not mean that the full spectrum of oxygen-transport factors was beneficially affected (Sutton, 1994). Although this variable is used frequently to indicate adaptation to exercise stress, that is only acceptable when exercise is the only stress. When adaptations are confounded between altitude and exercise stresses, it is illogical to attribute the changes to only altitude and to disregard other possibilities.
Statistical analyses of intergroup comparisons may not be sensitive enough to test altitude effects, particularly when group sizes are small. Perhaps intraindividual experimental designs would better reflect the effects of altitude exposure because of their removal of interindividual variation.
The literature shows that some individuals are assisted by altitude training while others are not and even some regress because of the stressful exposure (Daniels & Oldridge, 1970; Smith & Sharkey, 1984). The question arises that in the few who seem to be benefited by altitude exposure what are the mechanisms? Smith and Sharkey offer the following possibilities.
One study that is used extensively to justify the benefits of altitude training was conducted by Daniels and Oldridge (1970). Six world-class runners lived and trained intermittently at altitude (14-days at 2,300 m) and returned to sea-level for 5-day competitive periods. Performances at altitude and sea-level and results of physiological tests were reported. After each of the two altitude exposures, Jim Ryan returned to sea-level to run world-records. The majority of the other athletes also performed personal bests at each competition. These performances led the authors to conclude: "not only was training at altitude vital for sea-level athletes to compete at altitude, altitude training also seemed to be worthwhile for sea-level athletes wishing to perform well at sea-level" (p. 14). However, there were problems with this study's design which negate the conclusion that was postulated: (a) training at altitude was reduced in volume (taper) and increased in pace (specific quality), therefore, training effects could be the principal factor that produced the world-record and personal best performances; (b) there was no control group and so any inference about causality for the group is unjustified, and (c) interindividual variability did not allow general conclusions about any associations in the data.
The VO2max acclimatizations to altitude were particularly variable (a common finding in studies measuring altitude acclimatization and performance). Not only did values change, but the trends of the changes also varied (see Table 1). Some athletes improved from the first to the second exposure but then regressed from the second to the third exposure. At sea-level, only two of the six subjects exhibited an improved VO2max. There is no justification for concluding that there was a general trend of acclimatization to either sea-level or altitude conditions over the term of the study.
Table 1. Number of Ss Out of a Maximum of Six Exhibiting VO2max and Performance Changes Across Time and Conditions in the Original Daniels and Oldridge (1970) Study.
========================================================================= Test Comparison Nature of Change* No Change Worse Improved _________________________________________________________________________ Altitude 1 - Altitude 3 0 1 5 Altitude 1 - Altitude 5 2 1 3 Altitude 3 - Altitude 5 2 3 1 Sea-level 1 - Sea-level 2 4 0 2 Sea-level 1 - Sea-level Post 4 0 2 =========================================================================
* For a notable change to occur in VO2max values, test results had to differ by 2.0 ml/kg/min. If performances differed by more than two sec they were deemed to have changed.
Of particular note was the lack of similarity between physiological reactions and running performances. As sea-level and altitude performances improved, VO2max in one athlete worsened and in two others did not change. In three subjects, physiological factors improved prior to the first improved sea-level performances but worsened prior to the second improved sea-level performances. Inconsistencies such as these strongly suggest a lack of relationship between altitudinal physiological status and running performance. However, despite these deficiencies, there were some valid observations made and reported in the study.
Research shortcomings. Many Olympic and other coaches have accepted the spurious premise of altitude training (a specific acclimatization) somehow benefiting sea-level performance in elite athletes. This misconception largely originated in poor research designs in published studies. Major flaws have been: (a) small sample sizes (high variability and not good for generalizing results); (b) inadequate selection of subjects (few top-class athletes in peak training); (c) a lack of randomized subject assignment (results are biased especially in performance measures); (d) a failure to control the quantity and quality of work performed at altitude and at sea-level; (e) length of stay at altitude; and (f) the actual altitude experienced. Most significant research changes occur at high altitudes (e.g., >3,000 m) which are rarely experienced at training camps.
To be able to assess the adequacy of altitude research, strict evaluation of experimental control and study design has to be employed. Unless all factors which affect acclimatization and performance are controlled, and altitude is the only manipulated variable, it will not be possible to generate unequivocal conclusions. The potential is very high for producing confounded study results in this field of study which, in fact, has happened too often.
Many altitude-training advocates raise the Kenyan running successes as an example to justify altitude training, the popular perception being that all Kenyan runners live and train at altitude.
It was reported (Phillips, 1992) that Bengt Saltin studied Kenyan runners to answer some of the common assertions used to explain their superiority in world distance events. Saltin concluded the following.
The assumption that altitude training/living is responsible for Kenyan running successes is unfounded. Altitude training does not seem to be a variable that gives the Kenyans a competitive "edge" over the rest of the world. While living at altitude is good for aerobic development, training at altitude is not necessarily beneficial for sea-level performance (Phillips, 1992).
Despite the consistent failure of good research to support a beneficial effect of altitude training in highly trained athletes, the topic is still being investigated without any change in the topic status. A matched-control study was performed by Levine and Stray-Gundersen (20) using runners. Adaptations at altitudes of 2,500-3,000 m and 1,500 m (the pseudo-sea-level condition) were compared. Performance, field, and laboratory measures were similar for both groups with the lower altitude group also showing changes in sub-maximum measures of heart rate and lactate. One of the most recent studies concerning altitude training effects was conducted in Australia over the summer period of late 1993 and early 1994. Runners were matched into pairs and formed into training groups for altitude at Charlotte Pass (1,800 m) and sea-level at Narrabeen, New South Wales. Performance changes after training were evaluated at a neutral sea-level site that required the same amount of travel for both groups. The major finding was in agreement with Levine and Stray-Gundersen that both groups' performances improved similarly and that no advantage for sea-level performance was gained by training at altitude (Telford et al., 1996). When control groups have been adequately matched altitude training has not been shown to benefit sea-level performances.
Research using highly-trained swimmers has been sparse. Troup (1990, 1991, 1992) reported three years of observing swimmers train at Colorado Springs and sea-level as part of the work conducted by the International Center for Aquatic Research (ICAR). Upon review of these works two features were obvious: (a) some of the traditional shortcomings of adequate research (e.g., small group sizes, no control group) were evident in some of the studies, and (b) the early studies appeared to be interpreted as favoring altitude training benefits for sea-level performances, but that altered as investigations progressed. A 1991 study (Troup, 1992) was better formed with acceptably large group sizes, a control group, and objective evaluations of data. In spite of the recognized deficiencies in some parts of the studies, some acceptable data and findings were produced.
The belief that there is value in altitude exposure for enhancing sea-level performances is still promoted.
The latest approach includes two components: (a) train at sea-level so that training specificity and quantity will not be compromised, and (b) recover at altitude where the effects of altitude exposure may cause an exaggerated level of overcompensation in the recovery process following specific training stimulation (Rushall & Pyke, 1990, p. 138). This is loosely termed the "train low, recover high" (TLRH) concept.
There are several locations in Europe where it should be possible to train at sea-level and then be quickly transported to high altitude. Those opportunities usually are associated with alpine skiing resorts and valley-situated towns. In the USA an ideal location exists in the southern desert of California. It is possible to train at Palm Springs, a very low elevation, and then within half an hour be transported by aerial tramway to Mount San Jacinto State Park (elevation 3,000 m). In practical terms, that arrangement would minimize recovery at sea-level and maximize it at altitude. Finnish researchers have developed a "nitrogen house" that mimics the gas concentrations of altitude. It is used for living in (i.e., simulated altitude) after training at sea-level and constitutes a simulated TLRH condition.
There have been reports about the TLRH alternative. Five male endurance runners lived in a simulated TLRH environment for five days. A non-matched control group did not exhibit the hematological changes demonstrated by the experimental group (Puranen & Rusko, 1996). The training programs of the two groups were not controlled in that study. Changes in blood parameters were reported in six female cross-country runners after simulated TLRH living for 11 days (Rusko, Leppavouri, Makela, & Leppaluoto, 1995). In that investigation blood indices were not observed until they were stable and no matched control groups were used. As well, the measurements of the TLRH group were quite different to those of a total altitude training and recovery group which suggests that the TLRH condition is not equivalent to altitude acclimatization. Levine et al. (1990) reported that living at 2,500 m and training at 1,250 m produced increased VO2max and blood volume measures and 5,000 m run times that were superior to a group that trained and lived at 1,250 m. Simulated TLRH conditions produced changes in performance and blood variables in cyclists (Mattila & Rusko, 1996) but the absence of a control group weakens the value of those observations. Groups of competitive runners trained and lived at sea-level, at sea-level and altitude, or at altitude for both activities. The TLRH group improved in performance and some physiological variables. However, since the total sea-level group's performance was worse than at the very start of the investigation, the control over training content and stimulation quality has to be questioned and suggest inadequate control. Nummela, Jouste, and Rusko (1996) compared a group of male and female runners in simulated TLRH conditions with a group of males who experienced only sea-level conditions. The TLRH group improved in 400 m race time, velocity to exhaustion, and velocity at 5 mM lactate whereas the sea-level group did not.
While these reports suggest that changes occur with the TLRH experience, the quality of the research is questionable. As occurred with the investigation of altitude acclimatization effects, only when appropriate experimental controls are exhibited can one draw conclusions about a treatment. The TLRH research appears to be frequently repeating the design flaws of the acclimatization work. It is too early to embrace or reject the TLRH concept and caution is warranted until acceptable objective investigations are produced.
Several applied principles are supported by good research. The generalizations offered here relate to moderate altitudes (2,000 - 3,000 m).
The physiological changes that occur with acclimatization to altitude have been studied with varying degrees of proficiency. The circulatory system attempts to compensate for the decreased partial pressure of oxygen by enhancing certain characteristics, some of which are similar to those induced by physical training. Common reasoning asserts that if the characteristics of circulation at altitude are better than those of sea-level, then sea-level performances should be enhanced. There are serious flaws in such an argument. Firstly, circulation is not a limiting factor in extended endurance performances (e.g., >60 min) that require effort levels less than that which elicits a VO2max response. Even if there is an altitude-performance "improvement," it is not likely to influence highly-trained specific activities probably because of the different circulatory dynamics of altitude and sea-level performances (Wolski et al., 1996, p. 254). Second, altitude acclimatization does not mimic "blood doping" characteristics or effects. At altitude Hb concentration changes are coupled with other hematological and respiratory changes. This contrasts to sea-level "blood-doping" which only affects the Hb concentration in the blood. Thus, other moderating variables differentiate between the two physiological aberrations and it is inaccurate to assert the two "doping" phenomena are equivalent. Third, the major aerobic endurance changes that occur in training are particularly specific. Those of importance occur in the muscles. Altitude acclimatization does not enhance the specific (peripheral) nature of the sea-level endurance trained response. It could actually disrupt that state, particularly in events where the aerobic component is significant (e.g., 3,000 m of running; swimming races of 200 m and more).
The above reasonings add further to why altitude training is not the beneficial stimulus it is promoted to be. When confounding factors, for example, greater amounts of recovery and a less complicated and less stressful life-style, enter the altitude training experience, performance at subsequent sea-level events often is improved, but the actual value of altitude acclimatization has been masked by other performance-enhancing factors.
Coaches strive to produce marginal performance gains in elite swimmers. New training programs and variations of training stimuli often are promoted as "causes" for performance changes in exceptional athletes. Contrary to popular beliefs, physiological measures (e.g., VO2max, anaerobic threshold, hematological variables) do not differentiate performance levels among very top swimmers. Despite that fact, beneficial physiological improvements for sea-level swimming performances are deduced from the observed physiological changes that result from complete altitude acclimatization. Although it would seem logical that some increased aerobic components would increase endurance performance, pure physiological alterations usually do not transfer to specific combinations of biomechanical, physiological, and psychological factors, that is, specific performance.
Acclimatization to and training at altitude is governed by two principles of specificity. Specific acclimatization (adaptation) indicates that the changes which occur due to altitude are not necessarily beneficial for sea-level performance (Wolski et al., 1996, p. 258). Specific training requires that training be as close to intended competitive performances as possible in terms of energy requirements, neuromuscular patterns used, and psychological experiences for maximum training benefits to be derived (Kame, Pendergast, & Termin, 1990; Noakes, 1986; Stegeman, 1981, p. 258). With relevance to sea-level performances, neither of these two principles is facilitated by training at altitude.
Despite the consistent evidence about the lack of benefit of altitude training for sea-level performance, it is still a popular notion for training. Anyone who proposes altitude training has to adequately answer and explain the following questions.
It is the opinion of these authors that greater advances in sporting performances still can be gained by implementing verified principles of the sport science sub-disciplines of psychology, biomechanics, and physiology in a balanced fashion rather than seeking some single unusual factor such as an environmental alteration. Only when all the principles that are available are correctly implemented in the coaching process should further unresearched possibilities be considered. Few, if any, coaches currently train athletes according to all the applied principles of sporting performance that are associated with performance enhancement. For immediate performance improvements, it would be better to do correctly what is known, than to seek new avenues and possibilities such as altitude recovery.
One cannot lose sight of the difficulty to conduct altitude training experiments which are not flawed. While the conclusions of "flawed" studies continue to be repeated in the literature, false conclusions and implications for practitioners will be repeated.
There is no conclusive evidence that altitude acclimatization enhances training adaptations in specific exercises in trained high-performance swimmers. Training at and acclimatizing to altitude does not improve return-to-sea-level performances in such athletes.
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