Live high - train low altitude camps can enhance endurance power at sea level by 1-2% (Levine & Stray-Gunderson, 1997). More convenient methods to simulate altitude exposure are now available, but their effects on performance are less well characterized. In this study, we investigated intermittent hypoxic training (IHT) using an Hypoxicator, a device that produces oxygen-depleted air that athletes breathe intermittently through masks in a small group at a central venue. Twelve highly-competitive, male cyclists and multi-sport athletes (IHT group) underwent IHT in two, four-week bouts separated by eight weeks. Bout one consisted of 20 one-hour exposures and bout two 18 exposures where normal and low-oxygenated air was breathed in alternating five-minute intervals. The percentage of oxygen inhaled by the subjects was adjusted to produce an oxygen saturation of the blood of 88-92% in the first week of the study, decreasing to 76-80% (equivalent to an altitude of approximately 6000m) in the final week. A control group of 13 similar athletes did not use the Hypoxicator. Performance trials and blood tests were at four-week intervals; there were 3 trials (familiarization and reliability) before use of the Hypoxicator, 3 trials after to determine the effect of simulated altitude, then a second four-week exposure and one more trial. The measures of performance were mean power in a 16-km time trial on a Kingcycle ergometer (IHT group only) and power in a lactate-threshold test at 3 mmol/L above baseline (both groups). The measures from the blood tests were haemoglobin and haematocrit. There was a gradual but erratic improvement in performance in the time trial and lactate threshold tests over the course of the study in both groups, indicating an improvement through training. Relative to the last baseline test (Trial 3), the IHT group showed a 0.6% decrease in mean power over and above the effect of training in the 16-km time trial in Trial 4, nine days after last use of IHT. There was a 0.3% increase in mean power independent of the training effect in Trial 7, after the second round of altitude exposure. Uncertainty in these changes in performance was ±3.5% (95% confidence interval). The changes in lactate threshold in trials 4 and 7 indicate a possible improvement as a result of IHT exposure. Uncertainty in these changes was ±4.0%. There were negligible changes in the haemoglobin and hematocrit of either group at any time. There was small evidence of high responders, who were probably subjects with the DD genotype for the angiotensin converting enzyme gene. The time exposed to IHT had no bearing on performance and there was no evidence "peak" in results at either four or eight weeks after exposure to IHT. In summary, four weeks of IHT exposure probably resulted in a trivial effect on 16-km time-trial performance and the effort-independent measures provided no further clear-cut evidence of a performance improvement.

Live high - train low altitude camps can enhance endurance power at sea level by 1-2% (Levine & Stray-Gunderson, 1997). More convenient methods to simulate altitude exposure are now available, but their effects on performance are less well characterized. In this study, we investigated intermittent hypoxic training (IHT) using an Hypoxicator, a device that produces oxygen-depleted air that athletes breathe intermittently through masks in a small group at a central venue. Twelve highly-competitive, male cyclists and multi-sport athletes (IHT group) underwent IHT in two, four-week bouts separated by eight weeks. Bout one consisted of 20 one-hour exposures and bout two 18 exposures where normal and low-oxygenated air was breathed in alternating five-minute intervals. The percentage of oxygen inhaled by the subjects was adjusted to produce an oxygen saturation of the blood of 88-92% in the first week of the study, decreasing to 76-80% (equivalent to an altitude of approximately 6000m) in the final week. A control group of 13 similar athletes did not use the Hypoxicator. Performance trials and blood tests were at four-week intervals; there were 3 trials (familiarization and reliability) before use of the Hypoxicator, 3 trials after to determine the effect of simulated altitude, then a second four-week exposure and one more trial. The measures of performance were mean power in a 16-km time trial on a Kingcycle ergometer (IHT group only) and power in a lactate-threshold test at 3 mmol/L above baseline (both groups). The measures from the blood tests were haemoglobin and haematocrit. There was a gradual but erratic improvement in performance in the time trial and lactate threshold tests over the course of the study in both groups, indicating an improvement through training. Relative to the last baseline test (Trial 3), the IHT group showed a 0.6% decrease in mean power over and above the effect of training in the 16-km time trial in Trial 4, nine days after last use of IHT. There was a 0.3% increase in mean power independent of the training effect in Trial 7, after the second round of altitude exposure. Uncertainty in these changes in performance was ±3.5% (95% confidence interval). The changes in lactate threshold in trials 4 and 7 indicate a possible improvement as a result of IHT exposure. Uncertainty in these changes was ±4.0%. There were negligible changes in the haemoglobin and hematocrit of either group at any time. There was small evidence of high responders, who were probably subjects with the DD genotype for the angiotensin converting enzyme gene. The time exposed to IHT had no bearing on performance and there was no evidence "peak" in results at either four or eight weeks after exposure to IHT. In summary, four weeks of IHT exposure probably resulted in a trivial effect on 16-km time-trial performance and the effort-independent measures provided no further clear-cut evidence of a performance improvement.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work investigated the effect of intermittent hypoxic training (IHT) sessions under bodyweight, food intake and biochemical parameters in Wistar rats fed normo fat (NF) and high fat (HF) diets. Forty rats were divided in two groups, which were fed a NF or a HF diet. Afterwards the rats were subdivided in four groups and submitted to intermittent hypoxia (IH) or normoxia (N) sessions for 30 days. Groups formed: NF/N, NF/IH, HF/N and HF/IH. The groups submitted to IHT followed this protocol: 15 minutes hypoxia, 10-15% inspired O2 and 5 minutes for reoxigenation). Sham group was exposed to the same conditions but with normal O2 concentrations (21%). Bodyweight and food intake were measured every two days. The rats were anesthetized on day 31 and the blood was sampled by cardiac punction for analyses. The biochemical parameters analyzed were: total cholesterol (TC), triglycerides (TG), high density cholesterol (HDL), glucose, lactate dehidrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and muscle and hepatic glycogen. In regard to diets, the HF group promoted the biggest weight gain just in normoxia groups.The food intake decrease significantly in HF/IH subgroup compared to HF/N. Although the average of the corporal weight did not decrease significantly, the differences in percentages had shown a reduction in HF/IH subgroup. In the profile biochemist, the IHT only modified the LDH, increasing it in NF subgroup and the AST, diminishing it in HF subgroup. Our findings allow to suggest that the IHT can have a promising role in the prevention of the obesity and more studies are needed to evaluate its effect in the prevention/treatment of other diseases. / Este trabalho investigou o efeito de sessões de treinamento hipóxico intermitente (THI) sobre o peso corporal, consumo calórico e variáveis bioquímicas em ratos Wistar alimentados com dieta padrão (DP) ou dieta hipercalórica (DH). Quarenta ratos foram divididos em dois grupos e alimentados com DP ou DH. Na seqüência foram subdivididos em quatro grupos e submetidos às sessões de hipóxia intermitente (HI) ou normóxia (N) por 30 dias. Os grupos formados foram: DP/N, DP/HI, DH/N e DH/IH. Os grupos submetidos ao THI seguiram o seguinte protocolo: 15 minutos de hipóxia com a concentração de O2 inspirado variando entre 10 a 15% e 5 minutos para reoxigenação. Os grupos normóxia foram expostos às mesmas condições, porém com concentrações normais de O2 (21%). O peso corporal e o consumo de ração foram avaliados a cada dois dias. No dia 31, os animais foram anestesiados e o sangue foi coletado por punção cardíaca. As variáveis bioquímicas analisadas foram: colesterol total (CT), triglicerídeos (TG), lipoproteína de alta densidade (HDL), glicose, lactato desidrogenase (LDH), alanina aminotransferase (ALT), aspartato aminotransferase (AST), glicogênio muscular e hepático. Com relação às dietas, a DH promoveu maior ganho de peso somente nos grupos em normoxia. A ingesta calórica diminuiu significativamente no subgrupo DH/HI. Embora a média do peso corporal não tenha diminuído significativamente, as diferenças em percentagens mostraram uma redução no subgrupo DH/HI. No perfil bioquímico, o THI alterou somente a LDH, aumentando-a no subgrupo DP e a AST, diminuindo-a no subgrupo DH. Nossos achados permitem sugerir que o THI pode ter um papel promissor na prevenção da obesidade e mais estudos são necessários para avaliar seus efeitos na prevenção/tratamento de outras patologias.