Hypoxic Tent Research Articles

Hypoxia induces no change in cutaneous thresholds for warmth and cold sensation

Hypoxia can affect perception of temperature stimuli by impeding thermoregulation at a neural level. Whether this impact on the thermoregulatory response is solely due to affected thermoregulation is not clear, since reaction time may also be affected by hypoxia. Therefore, we studied the effect of hypoxia on thermal perception thresholds for warmth and cold. Thermal perception thresholds were determined in 11 healthy overweight adult males using two methods for small nerve fibre functioning: a reaction-time inclusive method of limits (MLI) and a reaction time exclusive method of levels (MLE). The subjects were measured under normoxic and hypoxic conditions using a cross-over design. Before the thermal threshold tests under hypoxic conditions were conducted, the subjects were acclimatized by staying 14 days overnight (8 h) in a hypoxic tent system (Colorado Altitude Training: 4,000 m). For normoxic measurements the same subjects were not acclimatized, but were used to sleep in the same tent system. Measurements were performed in the early morning in the tent. Normoxic MLI cold sensation threshold decreased significantly from 30.3 ± 0.4 (mean ± SD) to 29.9 ± 0.7°C when exposed to hypoxia (P < 0.05). Similarly, mean normoxic MLI warm sensation threshold increased from 34.0 ± 0.9 to 34.5 ± 1.1°C (P < 0.05). MLE measured threshold for cutaneous cold sensation was 31.4 ± 0.4 and 31.2 ± 0.9°C under respectively normoxic and hypoxic conditions (P > 0.05). Neither was there a significant change in MLE warm threshold comparing normoxic (32.8 ± 0.9°C) with hypoxic condition (32.9 ± 1.0°C) (P > 0.05). Exposure to normobaric hypoxia induces slowing of neural activity in the sensor-to-effector pathway and does not affect cutaneous sensation threshold for either warmth or cold detection.

The biochemistry of drugs and doping methods used to enhance aerobic sport performance

Optimum performance in aerobic sports performance requires an efficient delivery to, and consumption of, oxygen by the exercising muscle. It is probable that maximal oxygen uptake in the athlete is multifactorial, being shared between cardiac output, blood oxygen content, muscle blood flow, oxygen diffusion from the blood to the cell and mitochondrial content. Of these, raising the blood oxygen content by raising the haematocrit is the simplest acute method to increase oxygen delivery and improve sport performance. Legal means of raising haematocrit include altitude training and hypoxic tents. Illegal means include blood doping and the administration of EPO (erythropoietin). The ability to make EPO by genetic means has resulted in an increase in its availability and use, although it is probable that recent testing methods may have had some impact. Less widely used illegal methods include the use of artificial blood oxygen carriers (the so-called 'blood substitutes'). In principle these molecules could enhance aerobic sports performance; however, they would be readily detectable in urine and blood tests. An alternative to increasing the blood oxygen content is to increase the amount of oxygen that haemoglobin can deliver. It is possible to do this by using compounds that right-shift the haemoglobin dissociation curve (e.g. RSR13). There is a compromise between improving oxygen delivery at the muscle and losing oxygen uptake at the lung and it is unclear whether these reagents would enhance the performance of elite athletes. However, given the proven success of blood doping and EPO, attempts to manipulate these pathways are likely to lead to an ongoing battle between the athlete and the drug testers.

Drugs and ergogenic aids to improve sport performance

The use of biochemical aids to enhance athletic performance has a long history. In our current sporting culture we attempt to divide these between the accepted legal ‘ergogenic aids’ and the unacceptable performance-enhancing ‘drugs’. It is unclear whether this distinction would have been made 2000 years ago when Pliny the Elder reported the effects of Horsetail juice on performance. Interestingly, the sporting ergogenic effects of horsetail haven’t passed the test of time. In the middle ages its astringency, due to its high silica content, made it ideal for scouring pewter and wooden kitchen utensils. The juice's current ergogenic properties are more refined, its main use being in bath and shower products where a ‘natural conditioning effect’ is required. Perhaps more controversially, hidden amongst his 600 books, Claudius Galen, the 2nd century Greek physician to the gladiators, mentioned the positive effects of eating herbs, mushrooms and testicles. Galen believed that the right testicle was hotter and purer than the left, though whether this led to differential performance-enhancing effects was not rigorously tested. We shouldn't think that modern people are unusual in being obsessed with winning at all costs. Philostratos's (200 AD) view of the Ancient Greeks was that “They made war training for sport and sport training for war.” He was less impressed with his generation of sportsmen who “spent too much time eating, drinking and fornicating instead of actually training”. This was reflected in their poor choice of ergogenic aids. Although the ancient Spartan athletes trained on a meat-full diet of bulls, oxen, goats and deer, athletes of his generation ate white bread, poppy seeds, fish and pork [1]. They treated sports as “more of a hobby than a way of life”. Grumpy old men are clearly not a modern phenomenon! Clearly, if not actually preparing for war, … The use of biochemical aids to enhance athletic performance has a long history. In our current sporting culture we attempt to divide these between the accepted legal ‘ergogenic aids’ and the unacceptable performance-enhancing ‘drugs’. It is unclear whether this distinction would have been made 2000 years ago when Pliny the Elder reported the effects of Horsetail juice on performance. Interestingly, the sporting ergogenic effects of horsetail haven’t passed the test of time. In the middle ages its astringency, due to its high silica content, made it ideal for scouring pewter and wooden kitchen utensils. The juice's current ergogenic properties are more refined, its main use being in bath and shower products where a ‘natural conditioning effect’ is required. Perhaps more controversially, hidden amongst his 600 books, Claudius Galen, the 2nd century Greek physician to the gladiators, mentioned the positive effects of eating herbs, mushrooms and testicles. Galen believed that the right testicle was hotter and purer than the left, though whether this led to differential performance-enhancing effects was not rigorously tested. We shouldn't think that modern people are unusual in being obsessed with winning at all costs. Philostratos's (200 AD) view of the Ancient Greeks was that “They made war training for sport and sport training for war.” He was less impressed with his generation of sportsmen who “spent too much time eating, drinking and fornicating instead of actually training”. This was reflected in their poor choice of ergogenic aids. Although the ancient Spartan athletes trained on a meat-full diet of bulls, oxen, goats and deer, athletes of his generation ate white bread, poppy seeds, fish and pork [1]. They treated sports as “more of a hobby than a way of life”. Grumpy old men are clearly not a modern phenomenon! Clearly, if not actually preparing for war, …

Adaptación al aire enrarecido de las simas y cuevas. Estudio de laboratorio

Introduction and aimsThe atmosphere in the abysses of the mountains of Garraf (Barcelona) have lower oxygen levels and higher CO2 concentrations with respect to normality. To evaluate the risk of speleological exploration in this area, we studied 19 cavers (14 men and 5 women) while performing controlled exercise in a hypercapnic, hypoxic and normobaric atmosphere (15.2±0.8% of 299 O2 and 19,049±299 ppmv of CO2). MethodsThe study was performed in a laboratory through ergometry. Two identical tests were used: one in a standard atmosphere (NN) and another in a confined atmosphere (a hypoxic tent), with rarefied air (HH). The following parameters were monitored: electrocardiogram, heart rate, oxygen saturation of hemoglobin, lactate, capillary glycemia, and final blood pressure. ResultsThe volunteers had distinct symptoms during the test with rarefied air: heat sensation (100%), dizziness (47%), headache (3%), ocular pruritus (21%), hand tremor (16%), extrasystoles (16.5%), hypertonic blood pressure behavior (26%), tachycardia (158.5±15.9 bpm in rarefied air versus 148.7±15.7 bpm in normal air; p<0.0002).All participants showed reduced oxygen saturation (93.4±3.4% in rarefied air versus 97.7±9.92% in normal air; p<0.00004). DiscussionWide individual variability was found in symptoms and the parameters studied. In view of the results of this study, we recommend that a threshold of 45,000 ppmv of CO2 not be exceeded in speleological exploration. Likewise, fitness assessment should be performed in individuals planning to enter confined atmospheres, such as the caves and abysses of this mountain.

Response to “Prohibition of artificial hypoxic environments in sports: health risks rather than ethics”

We appreciate the comments made by Dr. Lippi, Dr. Franchini, and Dr. Guidi in response to our article ‘‘The spirit of sport, morality, and hypoxic tents: logic and authenticity’’ (Malloy et al. 2007). In their response, Lippi et al. have made a case for a prospective health risk associated with ‘‘excessive exposure to hypobaric hypoxia’’. The scientific evidence they report indicates that exposure to hypoxic environments — be they natural or artificial — beyond 3000 m presents a potential for significant physical risk. However, Levine and Stray-Gundersen (1992) suggest that an altitude of up to 4000 m is safe to facilitate the necessary physiological adjustments that improve sport performance. Consistent with the logic of the argument we presented, any training regime that places athletes in danger would be condemned. That is, teleologically, sleeping in a tent that replicates a dangerous environment (e.g., >4000 m) would be unacceptable — as would sleeping in the naturally, yet dangerously high, hypoxic environment of a mountain 5000 m above sea level to achieve the similar physiological adaptation. Both of these extremes take the hypoxic training strategy to a hazardous level and are therefore unacceptable. Having said this, extremes in training of any kind are potentially dangerous. For example, a progression of training volume (e.g., kilometres per week) or intensity is used by athletes as a necessary part of the training regime. However, if the progression in volume or intensity is too great, the athlete will be at an increased risk of injury. Thus, too much training too quickly is detrimental to both athletic performance and health. Some of the negative health outcomes associated with an inappropriate progression in training is an elevated resting heart rate, shin splints, decreased appetite, low energy levels, and depression. Reason seems to dictate that athletes are to avoid these dangerous extremes and seek what Aristotle (1968) would argue as ‘‘virtuous’’ training. He describes virtue as the mean between excess and deficit. To occupy either extreme is not only to choose badly, but also to damage the individual’s ‘‘soul’’. He states that

Prohibition of artificial hypoxic environments in sports: health risks rather than ethics

There is actual debate on a recent position of the World Anti-Doping Agency (WADA), which has cautiously refrained from banning hypoxic tents and intends to monitor their health risk. Regardless of teleological and deontological concepts, we highlight that the health risks inherent to the widespread use of these artificial performance-enhancing devices would make them as unsafe as other forms of blood doping.

Live High + Train Low: Thinking in Terms of an Optimal Hypoxic Dose

"Live high-train low" (LH+TL) altitude training allows athletes to "live high" for the purpose of facilitating altitude acclimatization, as characterized by a significant and sustained increase in endogenous erythropoietin and subsequent increase in erythrocyte volume, while simultaneously enabling them to "train low" for the purpose of replicating sea-level training intensity and oxygen flux, thereby inducing beneficial metabolic and neuromuscular adaptations. In addition to natural/terrestrial LH+TL, several simulated LH+TL devices have been developed including nitrogen apartments, hypoxic tents, and hypoxicator devices. One of the key issues regarding the practical application of LH+TL is what the optimal hypoxic dose is that is needed to facilitate altitude acclimatization and produce the expected beneficial physiological responses and sea-level performance effects. The purpose of this review is to examine this issue from a research-based and applied perspective by addressing the following questions: What is the optimal altitude at which to live, how many days are required at altitude, and how many hours per day are required? It appears that for athletes to derive the hematological benefits of LH+TL while using natural/terrestrial altitude, they need to live at an elevation of 2000 to 2500 m for =4 wk for =22 h/d. For athletes using LH+TL in a simulated altitude environment, fewer hours (12-16 h) of hypoxic exposure might be necessary, but a higher elevation (2500 to 3000 m) is required to achieve similar physiological responses.

Effect of Hypoxic "Dose" on Physiological Responses and Sea-Level Performance

Live high-train low (LH+TL) altitude training was developed in the early 1990s in response to potential training limitations imposed on endurance athletes by traditional live high-train high (LH+TH) altitude training. The essence of LH+TL is that it allows athletes to "live high" for the purpose of facilitating altitude acclimatization, as manifest by a profound and sustained increase in endogenous erythropoietin (EPO) and ultimately an augmented erythrocyte volume, while simultaneously allowing athletes to "train low" for the purpose of replicating sea-level training intensity and oxygen flux, thereby inducing beneficial metabolic and neuromuscular adaptations. In addition to "natural/terrestrial" LH+TL, several simulated LH+TL devices have been developed to conveniently bring the mountain to the athlete, including nitrogen apartments, hypoxic tents, and hypoxicator devices. One of the key questions regarding the practical application of LH+TL is, what is the optimal hypoxic dose needed to facilitate altitude acclimatization and produce the expected beneficial physiological responses and sea-level performance effects? The purpose of this paper is to objectively answer that question, on the basis of an extensive body of research by our group in LH+TL altitude training. We will address three key questions: 1) What is the optimal altitude at which to live? 2) How many days are required at altitude? and 3) How many hours per day are required? On the basis of consistent findings from our research group, we recommend that for athletes to derive the physiological benefits of LH+TL, they need to live at a natural elevation of 2000-2500 m for >or=4 wk for >or=22 h.d(-1).

The spirit of sport, morality, and hypoxic tents: logic and authenticity

The World Anti-Doping Agency (WADA) has recently made a decision to allow the use of hypoxic tents amid a significant amount of controversy over the morality of their use for athletic training purposes. Currently, altitude training is considered moral, but other means of improving aerobic performance are not; for example, blood doping. Altitude training and blood doping have similar results, but the methods by which the results are achieved differ greatly. The controversy lies in how the use of a hypoxic device falls within WADA's philosophy, which will then dictate future policy. This paper discusses the influence of a hypoxic environment on human physiology, altitude training's influence on athletic performance, the concept of authentic physiology, and moral behaviour that is the foundation for logical debate.

Intermittent Hypoxia does not Increase Exercise Ventilation at Simulated Moderate Altitude

Recent human studies have shown that resting hypoxic ventilatory response (HVR), which is an index of ventilatory chemosensitivity to hypoxia, increased after short-term intermittent hypoxia at rest. In addition, intermittent hypoxia leads to increases in ventilation and arterial oxygen saturation (SaO (2)) during exercise at simulated high altitude, with the increase in ventilation correlated to the change in HVR. However, no study has been made to clarify the relationship between ventilatory chemosensitivity and the exercise ventilation at moderate altitude following intermittent hypoxia during a resting state. The purpose of the present study, therefore, was to elucidate whether intermittent hypoxia at rest induces the increase in ventilation during exercise at moderate altitude that is accompanied by an increase in hypoxic chemosensitivity. Eighteen trained male runners were assigned to three groups, i.e., the first hypoxic group (H-1 group, n = 6), the second hypoxic group (H-2 group, n = 6), and a control group (C group, n = 6). The hypoxic tent system was utilized for intermittent hypoxia, and the oxygen levels in the tent were maintained at 15.5 +/- 0.1 % (simulated 2500 m altitude) for the H-1 group and 12.3 +/- 0.2 % (simulated 4300 m altitude) for the H-2 group. The H-1 and H-2 groups spent 1 hour per day in the hypoxic tent for 1 week. Maximal and submaximal exercise tests while breathing 15.5 +/- 0.01 % O (2) (simulated altitude of 2500 m) were performed before and after intermittent hypoxia. Resting HVR was also determined in each subject using a progressive isocapnic hypoxic method. In the H-2 group, HVR increased significantly (p < 0.05) following intermittent hypoxia, while no change in HVR was found in the H-1 or C group. Neither ventilation nor SaO (2) during maximal and submaximal exercise at a simulated altitude of 2500 m were changed in either group after 1 hour per day for 1 week of intermittent hypoxia. These results suggest that the change in resting hypoxic chemosensitivity after short-term intermittent hypoxia does not affect ventilation during exercise at moderate altitude.

Detection window of Darbepoetin-α following one single subcutaneous injection

Background The current official direct recombinant erythropoietin (rHuEPO) detection anti-doping test based on 1D isoelectric focusing (IEF) of urinary proteins was performed to determine the detection window of Darbepoietin-α when applying the positivity criteria established by the World Anti-Doping Agency (WADA). Results Following WADA's positivity criteria, the IEF based urinary EPO test enabled to determine that the detection window after a single subcutaneous injection of Darbepoietin-α (40 μg of ARANESP® injected) is close to 7 days, that is to say approximately two times more than for rHuEPO-β (4000 IU of Recormon® injected). The detection window can be different from one subject to another, because the actual positivity criteria take into consideration in someway the endogenous EPO production rate which differs enormously from one subject to another. That means, all subjects with a naturally elevated or stimulated EPO production rate (altitude training, hypoxic tent,…) have a reduced detection window for bone marrow stimulators such as Darbepoietin-α. Conclusion Darbepoietin-α has a much longer detection window in urine than any other available EPOs, which is a major disadvantage for illegal use in sports. The positivity criteria used up to now by all anti-doping laboratories are very conservative. Furthermore all athletes tested for rHuEPO are not equal regarding the actual test. For that reason, the criteria could be slightly adapted in the future, but further experiments are needed.

Diurnal normobaric moderate hypoxia raises serum erythropoietin concentration but does not stimulate accelerated erythrocyte production

This study was performed to examine the effect of diurnal normobaric hypoxia on hematological parameters. Eleven healthy male volunteers were randomly selected to be in either the hypoxic group (n=6) or the control group (n=5). The hypoxic group was exposed to 8 h of normobaric hypoxia in hypoxic tent systems that elicited a target peripheral O(2) saturation of 81+/-2% on three consecutive days. The control group spent three consecutive 8-h days in modified tent systems that delivered normoxic air into the tent. Venous blood samples were collected before the exposure (days -5, 0), after each day of the exposure (days 1, 2, 3), and for 3 weeks after the exposure (days 7, 10, 13, 17, 24). Serum erythropoietin concentration significantly increased from 9.1+/-3.3 U.L(-1) to 30.7+/-8.6 U.L(-1) in the hypoxic group. Although there were significant increases in hematocrit (4%), hemoglobin concentration (5%), red blood cell count (4%) on day 7 in the hypoxic group, these observations were likely due to dehydration or biological variation over time. There was no significant change in early erythropoietic markers (reticulocyte counts or serum ferritin concentration), which provided inconclusive evidence of accelerated erythroid differentiation and proliferation. The results suggest that the degree of hypoxia was sufficient to stimulate increased erythropoietin production and release. However, the duration of hypoxic exposure was insufficient to propagate the erythropoietic cascade.

Acute Sleep Responses in a Normobaric Hypoxic Tent

Acute Sleep Responses in a Normobaric Hypoxic Tent

Changes in Running Performance Following Intermittent Altitude Exposure Simulated With Tents

Exposure to natural altitude using the live high-train low method enhances endurance performance at sea level, but the effect of exposure to simulated altitude is less clear. PURPOSE To investigate the effect of intermittent hypoxia on sea-level performance by simulating altitude with hypoxic tents. METHODS Eleven male competitive runners and triathletes (age 31 ± 9 y, mean ± standard deviation) participated in a crossover study of usual training (control) and usual training with altitude exposure (altitude). Altitude treatment consisted of 25 ± 3 d (mean ± SD) of sleeping in tents for 8.1 ± 0.6 hr per day, progressing from a simulated altitude of 2500 m to 3500 m above sea level. Washout period between control and altitude treatments was 4 wk. Performance tests, scheduled 7 d after the control and altitude treatments, were three treadmill runs to exhaustion lasting ± 2, ± 4 and ± 8 min. Some athletes repeated the tests 5 d later. Times for standard competitions distances (800, 1500 and 3000 m) were predicted using a log-log model and analyzed by mixed modeling. Venous blood was sampled at 4 wk and 1 wk before and 1–7 d after altitude and control treatments RESULTS Effects of altitude exposure on predicted 800, 1500 and 3000 m performance were enhancements of 1.0% (90% confidence limits, ± 1.3%), 1.4% (± 1.2%) and 1.8% (± 1.5%) respectively. Enhancements were greater in the six athletes carrying an I allele for angiotensin converting enzyme (ACE): 2.3% (± 1.4%), 2.2% (± 1.4%), and 2.1%, (± 2.2%) respectively. For a smallest substantial change in performance of 0.5%, chances of real benefit were likely (>75%) and chances of real harm were very unlikely (<5%) for all these effects. The effects were apparently unrelated to oxygen carrying capacity of the blood, which showed a trend towards a decrease in mean values for hemoglobin concentration and hematocrit following the altitude treatment relative to the control. CONCLUSIONS The effects of altitude exposure on endurance performance after the use of hypoxic tents are worthwhile, but only for elite athletes. If further research supports the effects of the ACE genotype on performance, genotype assessment would make use of tents more cost effective.

Changes in Running Performance Following Intermittent Altitude Exposure Simulated With Tents

Exposure to natural altitude using the live high-train low method enhances endurance performance at sea level, but the effect of exposure to simulated altitude is less clear. PURPOSE To investigate the effect of intermittent hypoxia on sea-level performance by simulating altitude with hypoxic tents. METHODS Eleven male competitive runners and triathletes (age 31 ± 9 y, mean ± standard deviation) participated in a crossover study of usual training (control) and usual training with altitude exposure (altitude). Altitude treatment consisted of 25 ± 3 d (mean ± SD) of sleeping in tents for 8.1 ± 0.6 hr per day, progressing from a simulated altitude of 2500 m to 3500 m above sea level. Washout period between control and altitude treatments was 4 wk. Performance tests, scheduled 7 d after the control and altitude treatments, were three treadmill runs to exhaustion lasting ± 2, ± 4 and ± 8 min. Some athletes repeated the tests 5 d later. Times for standard competitions distances (800, 1500 and 3000 m) were predicted using a log-log model and analyzed by mixed modeling. Venous blood was sampled at 4 wk and 1 wk before and 1–7 d after altitude and control treatments RESULTS Effects of altitude exposure on predicted 800, 1500 and 3000 m performance were enhancements of 1.0% (90% confidence limits, ± 1.3%), 1.4% (± 1.2%) and 1.8% (± 1.5%) respectively. Enhancements were greater in the six athletes carrying an I allele for angiotensin converting enzyme (ACE): 2.3% (± 1.4%), 2.2% (± 1.4%), and 2.1%, (± 2.2%) respectively. For a smallest substantial change in performance of 0.5%, chances of real benefit were likely (>75%) and chances of real harm were very unlikely (<5%) for all these effects. The effects were apparently unrelated to oxygen carrying capacity of the blood, which showed a trend towards a decrease in mean values for hemoglobin concentration and hematocrit following the altitude treatment relative to the control. CONCLUSIONS The effects of altitude exposure on endurance performance after the use of hypoxic tents are worthwhile, but only for elite athletes. If further research supports the effects of the ACE genotype on performance, genotype assessment would make use of tents more cost effective.

Effect of a Repeated Series of Intermittent Hypoxic Exposures on Ventilatory Response in Humans

The purpose of this study was to elucidate the magnitude and the time course of ventilatory changes resulting from a repeated series of hypoxic exposures. Eight healthy males participated in the present study. The subjects spent 1 h/day in normobaric hypoxia (12% inspired oxygen). Inspired minute ventilation (V(I)), end-tidal partial pressure of carbon dioxide (P(ET(CO2))), and arterial oxygen saturation (SaO2) were measured in a hypoxic tent. These measurements were taken for 10 consecutive days (series 1), and were taken again after the subjects had been away from hypoxic exposure for 1 month (series 2). P(ET(CO2)) decreased and SaO2 increased progressively in the hypoxic tent during the 10 days of intermittent hypoxia in series 1. At the onset of series 2 (days 1 to 3), P(ET(CO2)) was significantly lower and SaO2 was significantly higher than those on day 1 during series 1. These results suggest that humans who have had previous hypoxic exposure adapt sooner to hypoxic condition due to an increase in the magnitude of hyperventilation in the first few days of a series of reexposures to hypoxia.

Changes in running endurance performance following intermittent altitude exposure simulated with tents

The effect of intermittent hypoxia on sea-level endurance performance was assessed by using hypoxic tents to simulate the live high-train low approach to altitude training. Eleven male sub-elite competitive runners and triathletes participated in a crossover study of usual training (control) and usual training with altitude exposure (altitude). Altitude treatment consisted of 25±3 d (mean±SD) of sleeping in tents for 8.1±0.6 h.d−1, progressing from a simulated altitude of 2500 m to 3500 m above sea level. Washout period between control and altitude treatments was 4 wk. Three treadmill runs to exhaustion lasting ∼2, ∼4 and ∼8 min were completed 7 and 12 d after control and altitude treatments. Times for standard competition distances (800, 1500 and 3000 m), were predicted using a log-log model, improved by 1.0% (90% confidence limits, ±1.3%), 1.4% (±1.2%) and 1.9% (±1.5%), respectively. Improvements were greater in the six athletes with an I allele for angiotensin converting enzyme (ACE): 2.3% (±1.5%), 2.2% (±1.5%), and 2.1%, (±2.1%), respectively. Effects of simulated altitude on hemoglobin concentration were unclear. Altitude exposure simulated with hypoxic tents is likely to enhance performance substantially in middle-distance endurance running events, especially for individuals with an I allele of the ACE gene.

Changes in ventilatory responses to hypercapnia and hypoxia after intermittent hypoxia in humans

The purpose of this study was to clarify the changes in hypercapnic and hypoxic ventilatory responses (HCVR and HVR) after intermittent hypoxia and following the cessation of hypoxic exposure. Twenty-nine males were assigned to one of four groups, i.e., a hypoxic (EX1-H, n=7) or a control (EX1-C, n=7) group in Experiment 1, and a hypoxic (EX2-H, n=8) or a control (EX2-C, n=7) group in Experiment 2. In each experiment, the hypoxic tent system was utilized for intermittent hypoxia, and the oxygen levels in the tent were maintained at 12.3+/-0.2%. In Experiment 1, the EX1-H group spent 3 h/day in the hypoxic tent for 1 week. HCVR and HVR were determined before and after 1 week of intermittent hypoxia, and again 1 and 2 week after the cessation of hypoxic exposure. In Experiment 2, the subjects in the EX2-H group performed 3 h/day for 2 weeks in intermittent hypoxia. HCVR and HVR tests were carried out before and after intermittent hypoxia, and were repeated again after 2 weeks of the cessation of hypoxic exposure. The slope of the HCVR in the EX1-H group did not show a significant increase after 1 week of intermittent hypoxia, while HCVR in the EX2-H group increased significantly after 2 weeks of intermittent hypoxia. The HCVR intercept was unchanged following 1 or 2 weeks of intermittent hypoxia. There was a significant increase in the slope of the HVR after 1 and 2 weeks of intermittent hypoxia. The increased HCVR and HVR returned to pre-hypoxic levels after 2 weeks of the cessation of hypoxia. These results suggest that 3 h/day for 2 weeks of intermittent hypoxia leads to an increase in central hypercapnic ventilatory chemosensitivity, which is not accompanied by a re-setting of the central chemoreceptors, and that the increased hypercapnic and hypoxic chemosensitivities are restored within 2 weeks after the cessation of hypoxia.