Application of altitude/hypoxic training by elite athletes

At the Olympic level, differences in performance are typically less than 0.5%. This helps explain why many contemporary elite endurance athletes in summer and winter sport incorporate some form of altitude/hypoxic training within their year-round training plan, believing that it will provide the "competitive edge" to succeed at the Olympic level. The purpose of this paper is to describe the practical application of altitude/hypoxic training as used by elite athletes. Within the general framework of the paper, both anecdotal and scientific evidence will be presented relative to the efficacy of several contemporary altitude/hypoxic training models and devices currently used by Olympic-level athletes for the purpose of legally enhancing performance. These include the three primary altitude/hypoxic training models: 1) live high+train high (LH+TH), 2) live high+train low (LH+TL), and 3) live low+train high (LL+TH). The LH+TL model will be examined in detail and will include its various modifications: natural/terrestrial altitude, simulated altitude via nitrogen dilution or oxygen filtration, and hypobaric normoxia via supplemental oxygen. A somewhat opposite approach to LH+TL is the altitude/hypoxic training strategy of LL+TH, and data regarding its efficacy will be presented. Recently, several of these altitude/hypoxic training strategies and devices underwent critical review by the World Anti-Doping Agency (WADA) for the purpose of potentially banning them as illegal performance-enhancing substances/methods. This paper will conclude with an update on the most recent statement from WADA regarding the use of simulated altitude devices.     

The ergogenics of hypoxia training in athletes

Hypoxia elicits hematopoiesis, which ultimately improves oxygen transport to peripheral tissues. In part because of this, altitude training has been used in the conditioning of elite endurance athletes for decades, despite equivocal evidence that such training benefits subsequent sea level performance. Recently, traditional live high-train high athletic conditioning has been implicated in a number of deleterious effects on training intensity, cardiac output, muscle composition, and fluid and metabolite balance —effects that largely offset hematopoietic benefits during sea level performance. Modifled live high-train low conditioning regimens appear to capture the beneficial hematopoietic effects of hypoxic training while avoiding many of the deleterious effects of training at altitude. Because of the logistical and financial barriers to living high and training low, various methods to simulate hypoxia have been developed and studied. The data from these studies suggest a threshold requirement for hypoxic exposure to meaningfully augment hematopoiesis, and presumably improve athletic performance.     

Introduction to altitude/hypoxic training symposium

Altitude/hypoxic training has traditionally been an intriguing and controversial area of research and sport performance. This controversial aspect was evident recently in the form of scholarly debates in highly regarded professional journals, as well as the World Anti-Doping Agency's (WADA) consideration of placing "artificially-induced hypoxic conditions" on the 2007 Prohibited List of Substances/Methods. In light of the ongoing controversy surrounding altitude/hypoxic training, this symposium was organized with the following objectives in mind: 1) to examine the primary physiological responses and underlying mechanisms associated with altitude/hypoxic training, including the influence of genetic predisposition; 2) to present evidence supporting the effect of altitude/hypoxic acclimatization on both hematological and nonhematological markers, including erythrocyte volume, skeletal muscle-buffering capacity, hypoxic ventilatory response, and physiological efficiency/economy; 3) to evaluate the efficacy of several contemporary simulated altitude modalities and training strategies, including hypoxic tents, nitrogen apartments, and intermittent hypoxic exposure (IHE) or training, and to address the legal and ethical issues associated with the use of simulated altitude; and 4) to describe different altitude/hypoxic training strategies used by elite-level athletes, including Olympians and military special forces. In addressing these objectives, papers will be presented on the topics of: 1) effect of hypoxic "dose" on physiological responses and sea-level performance (Drs. Benjamin Levine and James Stray-Gundersen), 2) nonhematological mechanisms of improved performance after hypoxic exposure (Dr. Christopher Gore), 3) application of altitude/hypoxic training by elite athletes (Dr. Randall Wilber), and 4) military applications of hypoxic training (Dr. Stephen Muza).     

Intermittent hypoxic training: fact and fancy

Intermittent hypoxic training (IHT) refers to the discontinuous use of normobaric or hypobaric hypoxia, in an attempt to reproduce some of the key features of altitude acclimatization, with the ultimate goal to improve sea-level athletic performance. In general, IHT can be divided into two different strategies: (1) providing hypoxia at rest with the primary goal being to stimulate altitude acclimatization or (2) providing hypoxia during exercise, with the primary goal being to enhance the training stimulus. Each approach has many different possible application strategies, with the essential variable among them being the "dose" of hypoxia necessary to achieve the desired effect. One approach, called living high-training low, has been shown to improve sea-level endurance performance. This strategy combines altitude acclimatization (2500 m) with low altitude training to ensure high-quality training. The opposite strategy, living low-training high, has also been proposed by some investigators. The primacy of the altitude acclimatization effect in IHT is demonstrated by the following facts: (1) living high-training low clearly improves performance in athletes of all abilities, (2) the mechanism of this improvement is primarily an increase in erythropoietin, leading to increased red cell mass, V(O2max), and running performance, and (3) rather than intensifying the training stimulus, training at altitude or under hypoxia leads to the opposite effect - reduced speeds, reduced power output, reduced oxygen flux - and therefore is not likely to provide any advantage for a well-trained athlete.     

The effect of a sleep high-train low regimen on the finger cold-induced vasodilation response

The present study evaluated the effect of a sleep high-train low regimen on the finger cold-induced vasodilation (CIVD) response. Seventeen healthy males were assigned to either a control (CON; n=9) or experimental (EXP; n=8) group. Each group participated in a 28-day aerobic training program of daily 1-h exercise (50% of peak power output). During the training period, the EXP group slept at a simulated altitude of 2800 meters (week 1) to 3400?m (week 4) above sea level. Normoxic (CIVD(NOR); CON and EXP groups) and hypoxic (CIVD(HYPO); F(I)O(2)=0.12; EXP group only) CIVD characteristics were assessed before and after the training period during a 30-min immersion of the hand in 8°C water. After the intervention, the EXP group had increased average finger skin temperature (CIVD(NOR): +0.5°C; CIVD(HYPO): +0.5°C), number of waves (CIVD(NOR): +0.5; CIVD(HYPO): +0.6), and CIVD amplitude (CIVD(NOR): +1.5°C; CIVD(HYPO): +3°C) in both CIVD tests (p<0.05). In contrast, the CON group had an increase in only the CIVD amplitude (+0.5°C; p<0.05). Thus, the enhancement of aerobic performance combined with altitude acclimatization achieved with the sleep high-train low regimen contributed to an improved finger CIVD response during cold-water hand immersion in both normoxic and hypoxic conditions.     

Current trends in altitude training

Recently, endurance athletes have used several novel approaches and modalities for altitude training including: (i) normobaric hypoxia via nitrogen dilution (hypoxic apartment); (ii) supplemental oxygen; (iii) hypoxic sleeping devices; and (iv) intermittent hypoxic exposure (IHE). A normobaric hypoxic apartment simulates an altitude environment equivalent to approximately 2000 to 3000m (6560 to 9840ft). Athletes who use a hypoxic apartment typically 'live and sleep high' in the hypoxic apartment for 8 to 18 hours a day, but complete their training at sea level, or approximate sea level conditions. Several studies suggest that using a hypoxic apartment in this manner produces beneficial changes in serum erythropoietin (EPO) levels, reticulocyte count and red blood cell (RBC) mass, which in turn may lead to improvements in postaltitude endurance performance. However, other studies failed to demonstrate significant changes in haematological indices as a result of using a hypoxic apartment. These discrepancies may be caused by differences in methodology, the hypoxic stimulus that athletes were exposed to and/or the training status of the athletes. Supplemental oxygen is used to simulate either normoxic (sea level) or hyperoxic conditions during high-intensity workouts at altitude. This method is a modification of the 'high-low' strategy, since athletes live in a natural terrestrial altitude environment but train at 'sea level' with the aid of supplemental oxygen. Limited data regarding the efficacy of hyperoxic training suggests that high-intensity workouts at moderate altitude (1860m/6100ft) and endurance perfor- mance at sea level may be enhanced when supplemental oxygen training is utilised at altitude over a duration of several weeks. Hypoxic sleeping devices include the Colorado Altitude Training (CAT) Hatch (hypobaric chamber) and Hypoxico Tent System (normobaric hypoxic system), both of which are designed to allow athletes to sleep high and train low. These devices simulate altitudes up to approximately 4575 m/15006 ft and 4270 m/14005 ft, respectively. Currently, no studies have been published on the efficacy of these devices on RBC production, maximal oxygen uptake and/or performance in elite athletes. IHE is based on the assumption that brief exposures to hypoxia (1.5 to 2.0 hours) are sufficient to stimulate the release of EPO, and ultimately bring about an increase in RBC concentration. Athletes typically use IHE while at rest, or in conjunction with a training session. Data regarding the effect of IHE on haematological indices and athletic performance are minimal and inconclusive.     

Classical altitude training

For more than 40 years, the effects of classical altitude training on sea-level performance have been the subject of many scientific investigations in individual endurance sports. To our knowledge, no studies have been performed in team sports like football. Two well-controlled studies showed that living and training at an altitude of ≥1800–2700 m for 3–4 weeks is superior to equivalent training at sea level in well-trained athletes. Most of the controlled studies with elite athletes did not reveal such an effect. However, the results of some uncontrolled studies indicate that sea-level performance might be enhanced after altitude training also in elite athletes. Whether hypoxia provides an additional stimulus for muscular adaptation, when training is performed with equal intensity compared with sea-level training is not known. There is some evidence for an augmentation of total hemoglobin mass after classical altitude training with duration ≥3 weeks at an altitude ≥2000 m due to altitude acclimatization. Considerable individual variation is observed in the erythropoietic response to hypoxia and in the hypoxia-induced reduction of aerobic performance capacity during training at altitude, both of which are thought to contribute to inter-individual variation in the improvement of sea-level performance after altitude training.     

Exercise economy does not change after acclimatization to moderate to very high altitude

For more than 60 years, muscle mechanical efficiency has been thought to remain unchanged with acclimatization to high altitude. However, recent work has suggested that muscle mechanical efficiency may in fact be improved upon return from prolonged exposure to high altitude. The purpose of the present work is to resolve this apparent conflict in the literature. In a collaboration between four research centers, we have included data from independent high-altitude studies performed at varying altitudes and including a total of 153 subjects ranging from sea-level (SL) residents to high-altitude natives, and from sedentary to world-class athletes. In study A (n=109), living for 20-22 h/day at 2500 m combined with training between 1250 and 2800 m caused no differences in running economy at fixed speeds despite low typical error measurements. In study B, SL residents (n=8) sojourning for 8 weeks at 4100 m and residents native to this altitude (n=7) performed cycle ergometer exercise in ambient air and in acute normoxia. Muscle oxygen uptake and mechanical efficiency were unchanged between SL and acclimatization and between the two groups. In study C (n=20), during 21 days of exposure to 4300 m altitude, no changes in systemic or leg VO(2) were found during cycle ergometer exercise. However, at the substantially higher altitude of 5260 m decreases in submaximal VO(2) were found in nine subjects with acute hypoxic exposure, as well as after 9 weeks of acclimatization. As VO(2) was already reduced in acute hypoxia this suggests, at least in this condition, that the reduction is not related to anatomical or physiological adaptations to high altitude but to oxygen lack because of severe hypoxia altering substrate utilization. In conclusion, results from several, independent investigations indicate that exercise economy remains unchanged after acclimatization to high altitude.     

Physiological responses to exercise at altitude : an update

Studies performed over the past decade have yielded new information related to the physiological and metabolic adjustments made in response to both short- and long-term high-altitude exposure. These investigations have examined the potential mechanisms responsible for the alterations observed in such key variables as heart rate, stroke volume, cardiac output, muscle blood flow, substrate utilization and mitochondrial function, both at rest and during exercise of varying intensities. Additionally, the occurrence and mechanisms related to the 'lactate paradox' continues to intrigue investigators. It is apparent that exposure to high altitude is an environmental stressor that elicits a robust sympathoadrenal response that contributes to many of the critical adjustments and adaptations mentioned above. Furthermore, as some of these important physiological adaptations are known to enhance performance, it has become popular to incorporate an aspect of altitude living/training into the training regimens of endurance athletes (e.g. 'live high-train low'). Finally, it is important to note that many factors influence the extent to which individuals adjust and adapt to the stress imposed by exposure to high altitude. Included among these are (i) the degree of hypoxia; (ii) the duration of exposure to hypoxic conditions; (iii) the exercise intensity (absolute vs relative workload); and (iv) the inter-individual variability in adapting to hypoxic environments ('responders' vs 'non-responders').     

A three-week traditional altitude training increases hemoglobin mass and red cell volume in elite biathlon athletes

It is well known that altitude training stimulates erythropoiesis, but only few data are available concerning the direct altitude effect on red blood cell volume (RCV) in world class endurance athletes during exposure to continued hypoxia. The purpose of this study was to evaluate the impact of three weeks of traditional altitude training at 2050 m on total hemoglobin mass (tHb), RCV and erythropoietic activity in highly-trained endurance athletes. Total hemoglobin mass, RCV, plasma volume (PV), and blood volume (BV) from 6 males and 4 females, all members of a world class biathlon team, were determined on days 1 and 20 during their stay at altitude as well as 16 days after returning to sea-level conditions (800 m, only males) by using the CO-rebreathing method. In males tHb (14.0 +/- 0.2 to 15.3 +/- 1.0 g/kg, p < 0.05) and RCV (38.9 +/- 1.5 to 43.5 +/- 3.9 ml/kg, p < 0.05) increased at altitude and returned to near sea-level values 16 days after descent. Similarly in females, tHb (13.0 +/- 1.0 to 14.2 +/- 1.3 g/kg, p < 0.05) and RCV (37.3 +/- 3.3 to 42.2 +/- 4.1 ml/kg, p < 0.05) increased. Compared to their sea-level values, the BV of male and female athletes showed a tendency to increase at the end of the altitude training period, whereas PV was not altered. In male athletes, plasma erythropoietin concentration increased up to day 4 at altitude (11.8 +/- 5.0 to 20.8 +/- 6.0 mU/ml, p < 0.05) and the plasma concentration of the soluble transferrin receptor was elevated by about 11 % during the second part of the altitude training period, both parameters indicating enhanced erythropoietic activity. In conclusion, we show for the first time that a three-week traditional altitude training increases erythropoietic activity even in world class endurance athletes leading to elevated tHb and RCV. Considering the relatively fast return of tHb and RCV to sea-level values after hypoxic exposure, our data suggest to precisely schedule training at altitude and competition at sea level.     

Improving athletic performance: is altitude residence or altitude training helpful?

Exercise training studies conducted at different altitudes (1250-5700 m) of varying durations (30 min to 19 wk) are critically reviewed to determine the efficacy of using altitude as a training stimulus to enhance sea level and altitude exercise performance. Four strategies are discussed: a) exercise training while residing at the same altitude; b) exercise training at altitude but residing at sea level; c) exercise training at low altitude but residing at a higher altitude; and d) exercise training under sea level and altitude conditions but only after altitude acclimatization has occurred. Residing at altitude causes a multitude of potentially beneficial physiological, ventilatory, hematological and metabolic changes that theoretically should induce a potentiating effect on endurance exercise performance. While it is accepted that endurance performance is greatly enhanced at altitude, there is less support for the view that altitude training while residing at altitude improves subsequent sea level endurance performance. There is some evidence, though also not universally accepted, that training at altitude but residing at sea level may benefit sea level endurance performance. Most recently, the combination of "living high" (e.g., at 2500 m) to obtain beneficial physiological changes associated with altitude acclimatization and "training low" (e.g., at 1250 m) to allow maintenance of high-intensity training is accumulating scientific and popular support as the most advantageous strategy to improve subsequent sea level exercise performance in well-trained, competitive runners.     

Effects of intermittent exposure to high altitude on blood volume and erythropoietic activity

The purpose of this review is to describe changes in blood volume and erythropoietic activity occurring under different types of intermittent exposure to hypoxia. These hypoxic episodes can vary from a few seconds or minutes to hours, days, or even weeks. Short hypoxic episodes like sleep apnea only lead to a small increase in hemoglobin concentration, which is mainly due to a hormonal-mediated decrease in plasma volume. In most of these cases the cumulative time spent under hypoxia does not exceed the critical threshold of about 90 min. Endurance athletes and mountaineers who voluntarily expose themselves to hypoxia for some hours or during the night while spending the day at normoxia ("sleep high-train low" concept) do improve their physical performance. Despite raising erythropoietic activity, indicated by elevated plasma concentrations of EPO and the transferrin receptor, the postulated increase in red cell volume has not satisfactorily been proved. Frequent changes between low and high altitudes, which are usual in some South American and Asian countries, provoke similar adaptations in red cell mass as occur in high altitude residents. However, the plasma volume decreases at altitude and increases again when staying at sea level. Even after more than 20 yr of regular moving between low and high altitude, the total blood volume, hemoglobin concentration and hematocrit, as well as the plasma EPO concentration, noticeably oscillate during every hypoxic-normoxic cycle. We assume these changes to be an optimal rapid adaptation of the oxygen transport system to the prevailing hypoxic or normoxic environment. However, possible risks for the organism cannot be excluded.     

中日联合阿尼玛卿山医学科学考察——人在极高高原的生理研究

为了探讨人在极高高原的低氧生理适应,考察队在急速进抵阿尼玛卿山(海拔6282m)进行了一项综合性的生理学研究。在4个不同海拔(2261m,3719m,4 904m及5 200m)动态地检测了静息及运动负荷下的心肺功能、心电图改变、运动动脉血氧饱和度、球结膜微循环、神经反应时、睡眠特征、凝血因子、能量消耗与体重丧失,急性高山病的发生率及生理学评价指标,同时进行了低氧动物实验研究。本研究获取了大量有意义的高原生理资料,特别在若干生理反应和急性高山病的发生率上在汉族队员与藏族世居者间存在明显差别,提示他们生理适应方式的差别和高原藏族的适应优势。     

Military applications of hypoxic training for high-altitude operations

Rapid deployment of unacclimatized soldiers to high mountainous environments causes debilitating effects on operational capabilities (physical work performance), and force health (altitude sickness). Most of these altitude-induced debilitations can be prevented or ameliorated by a wide range of physiological responses collectively referred to as altitude acclimatization. Acclimatization to a target altitude can be induced by slow progressive ascents or continuous sojourns at intermediate altitudes. However, this "altitude residency" requirement reduces their utilization in rapid response military missions that exploit the air mobility capability of modern military forces to quickly deploy to an area of operations on short notice. A more recent approach to induce altitude acclimatization is the use of daily intermittent hypoxic exposures (IHE) in lieu of continuous residence at high altitudes. IHE treatments consist of three elements: 1) IHE simulated altitude (inspired oxygen partial pressure: PIO2), 2) IHE session duration, and 3) total number of IHE sessions over the treatment period. This paper reviews and summarizes the results of 25 published IHE studies. This review finds that an IHE altitude>or=4000 m, and daily exposure duration of at least 1.5 h repeated over a week or more are required to have a high probability of developing altitude acclimatization. The efficacy of shorter duration (<1.5 h) hypoxic exposures at >or=4000 m simulated altitudes, and longer exposures (>4 h) at moderate altitudes (2500-3500 m) is not well documented. The predominate IHE-induced altitude acclimatization response appears to be increased arterial oxygen content through ventilatory acclimatization. Thus, IHE is a promising approach to provide the benefits of altitude acclimatization to low-altitude-based soldiers before their deployment to high mountainous regions.     

Effects of intermittent hypoxia on heart rate variability during rest and exercise

Changes in heart rate variability induced by an intermittent exposure to hypoxia were evaluated in athletes unacclimatized to altitude. Twenty national elite athletes trained for 13 days at 1200 m and either lived and slept at 1200 m (live low, train low, LLTL) or between 2500 and 3000 m (live high, train low, LHTL). Subjects were investigated at 1200 m prior to and at the end of the 13-day training camp. Exposure to acute hypoxia (11.5% O(2)) during exercise resulted in a significant decrease in spectral components of heart rate variability in comparison with exercise in normoxia: total power (p < 0.001), low-frequency component. LF (p < 0.001), high-frequency component, HF (p < 0.05). Following acclimatization, the LHTL group increased its LF component (p < 0.01) and LF/HF ratio during exercise in hypoxia after the training period. In parallel, exposure to intermittent hypoxia caused an increased ventilatory response to hypoxia. Acclimatization modified the correlation between the ventilatory response to hypoxia at rest and the difference in total power between normoxia and hypoxia (r (2) = 0.65, p < 0.001). The increase in total power, LF component, and LF/HF ratio suggests that intermittent hypoxic training increased the response of the autonomic nervous system mainly through increased sympathetic activity.     

Erythropoiesis and performance after two weeks of living high and training low in well trained triathletes

The purpose of our study was to evaluate hematologic acclimatization during 2 weeks of intensive normoxic training with regeneration at moderate altitude (living high-training low, LHTL) and its effects on sea-level performance in well trained athletes compared to another group of equally trained athletes under control conditions (living low - training low, CONTROL). Twenty-one triathletes were ascribed either to LHTL (n = 11; age: 23.0 +/- 4.3 yrs; VO 2 max: 62.5 +/- 9.7 [ml x min -1 x kg -1]) living at 1956 m of altitude or to CONTROL (n = 10; age: 18.7 +/- 5.6 yrs; VO 2 max: 60.5 +/- 6.7 ml x min -1 x kg -1) living at 800 m. Both groups performed an equal training schedule at 800 m. VO 2 max, endurance performance, erythropoietin in serum, hemoglobin mass (Hb tot, CO-rebreathing method) and hematological quantities were measured. A tendency to improved performance in LHTL after the camp was not significant (p < 0.07). Erythropoietin concentration increased temporarily in LHTL (Delta 14.3 +/- 8.7 mU x ml -1; p < 0.012). Hb tot remained unchanged in LHTL whereas was slightly decreased from 12.5 +/- 1.3 to 11.9 +/- 1.3g x kg -1 in CONTROL (p < 0.01). As the reticulocyte number tended to higher values in LHTL than in CONTROL, it seems that a moderate stimulation of erythropoiesis during regeneration at altitude served as a compensation for an exercise-induced destruction of red cells.     

The effect of intermediate altitude on the Army Physical Fitness Test.

Official physical training records of personnel stationed at intermediate altitude (elevation 5,280 feet) for at least 1 year were reviewed to gauge the effect of altitude on 2-mile running performance. An average of 48 additional seconds (a 5% increase in time) was required to complete the run compared to sea-level values in the same subjects. Run times gradually diminished during the first 9 months of assignment to altitude before stability was established. These data indicate that acclimatization occurs over several months. Even with acclimatization, substantial loss of performance is associated with habitation at intermediate altitude.     

Effect of F(I)O(2) on physiological responses and cycling performance at moderate altitude

PURPOSE: To evaluate physiological responses and exercise performance during a "live high-train low via supplemental oxygen" (LH + TLO(2)) interval workout in trained endurance athletes. METHODS: Subjects (N = 19) were trained male cyclists who were permanent residents of moderate altitude (1800-1900 m). Testing was conducted at 1860 m (P(B) 610-612 Torr, P(I)O(2) approximately 128 Torr). Subjects completed three randomized, single-blind trials in which they performed a standardized interval workout while inspiring a medical-grade gas with F(I)O(2) 0.21 (P(I)O(2) approximately 128 Torr), F(I)O(2) 0.26 (P(I)O(2) approximately 159 Torr), and F(I)O(2) 0.60 (P(I)O(2) approximately 366 Torr). The standardized interval workout consisted of 6 x 100 kJ performed on a dynamically calibrated cycle ergometer at a self-selected workload and pedaling cadence with a work:recovery ratio of 1:1.5. RESULTS: Compared with the control trial (21% O(2)), average total time (min:s) for the 100-kJ work interval was 5% and 8% (P < 0.05) faster in the 26% O(2) and 60% O(2) trials, respectively. Consistent with the improvements in total time were increments in power output (W) equivalent to 5% (26% O(2) trial) and 9% (60% O(2) trial; P < 0.05). Whole-body [VO](2) (L.min-1) was higher by 7% and 14% (P < 0.05) in the 26% O(2) and 60% O(2) trials, respectively, and was highly correlated to the improvement in power output (r = 0.85, P < 0.05). Arterial oxyhemoglobin saturation (S(p)O(2)) was significantly higher by 5% (26% O(2)) and 8% (60% O(2)) in the supplemental oxygen trials. CONCLUSION: We concluded that a typical LH + TLO(2) training session results in significant increases in arterial oxyhemoglobin saturation, [V02] and average power output contributing to a significant improvement in exercise performance.     

Hemoglobin mass after 21 days of conventional altitude training at 1816 m

The underlying mechanisms of altitude training are still a matter of controversial discussion but erythropoietic adaptations with an increase of total haemoglobin mass (tHb) have been shown in several studies, partly depending on an adequate hypoxic dose. The aim of this retrospective study was to investigate if a 3 weeks sojourn at moderate altitude (1816 m) with conventional training sessions (live and train at moderate altitude), especially under real and uncontrolled conditions, results in an increased tHb. tHb was measured in seven male cyclists competing at elite level (German national cycling team, U23 category) prior to the ascent to altitude and immediately after descent to sea-level. The athletes completed a 21 days altitude training camp living at 1816 m and training at 1800–2400 m during the competitive season. No significant difference was found in tHb after the altitude sojourn (prior 927 ± 109 g vs. 951 ± 113 g post, 95% CI ?13–61 g). Additionally, the analysis of red cell volume, plasma volume and blood volume or haemoglobin concentration [Hb] as well as haematocrit (Hct) did not reveal any significant changes. The data supports the theory that an adequate hypoxic dose is required for adaptations of the erythropoietic system with an increase of tHb and a threshold of approximately 2100–2500 m has to be exceeded.