The Impact of Normobaric Hypoxia and Intermittent Hypoxic Training on Cardiac Biomarkers in Endurance Athletes: A Pilot Study.

This study explores the effects of normobaric hypoxia and intermittent hypoxic training (IHT) on the physiological condition of the cardiac muscle in swimmers. Hypoxia has been reported to elicit both beneficial and adverse changes in the cardiovascular system, but its impact on the myocardium during acute exercise and altitude/hypoxic training remains less understood. We aimed to determine how a single bout of intense interval exercise and a four-week period of high-intensity endurance training under normobaric hypoxia affect cardiac marker activity in swimmers. Sixteen young male swimmers were divided into two groups: one undergoing training in hypoxia and the other in normoxia. Cardiac markers, including troponin I and T (cTnI and cTnT), heart-type fatty acid-binding protein (H-FABP), creatine kinase-MB isoenzyme (CK-MB), and myoglobin (Mb), were analyzed to assess the myocardium's response. We found no significant differences in the physiological response of the cardiac muscle to intense physical exertion between hypoxia and normoxia. Four weeks of IHT did not alter the resting levels of cTnT, cTnI, and H-FABP, but it resulted in a noteworthy decrease in the resting concentration of CK-MB, suggesting enhanced cardiac muscle adaptation to exercise. In contrast, a reduction in resting Mb levels was observed in the control group training in normoxia. These findings suggest that IHT at moderate altitudes does not adversely affect cardiac muscle condition and may support cardiac muscle adaptation, affirming the safety and efficacy of IHT as a training method for athletes.

The effect of normobaric hypoxia on acute exercise-induced changes in blood sphingoid base-1-phosphates metabolism in cyclists.

Extracellular sphingosine-1-phosphate (S1P) emerged as an important regulator of muscle function. We previously found that plasma S1P concentration is elevated in response to acute exercise and training. Interestingly, hypoxia, which is commonly utilized in training programs, induces a similar effect. Therefore, the aim of the current study was to determine the effect of normobaric hypoxia on exercise-induced changes in blood sphingolipid metabolism. Fifteen male competitive cyclists performed a graded cycling exercise until exhaustion (GE) and a simulated 30 km individual time trial (TT) in either normoxic or hypoxic (FiO2 = 16.5%) conditions. Blood samples were taken before the exercise, following its cessation, and after 30 min of recovery. We found that TT increased dihydrosphingosine-1-phosphate (dhS1P) concentration in plasma (both HDL- and albumin-bound) and blood cells, as well as the rate of dhS1P release from erythrocytes, regardless of oxygen availability. Plasma concentration of S1P was, however, reduced during the recovery phase, and this trend was augmented by hypoxia. On the other hand, GE in normoxia induced a selective increase in HDL-bound S1P. This effect disappeared when the exercise was performed in hypoxia, and it was associated with reduced S1P level in platelets and erythrocytes. We conclude that submaximal exercise elevates total plasma dhS1P concentration via increased availability of dihydrosphingosine resulting in enhanced dhS1P synthesis and release by blood cells. Maximal exercise, on the other hand, induces a selective increase in HDL-bound S1P, which is a consequence of mechanisms not related to blood cells. We also conclude that hypoxia reduces post-exercise plasma S1P concentration.

Exercise-Induced Elevated BDNF Level Does Not Prevent Cognitive Impairment Due to Acute Exposure to Moderate Hypoxia in Well-Trained Athletes.

Exposure to acute hypoxia causes a detrimental effect on the brain which is also manifested by a decrease in the ability to perform psychomotor tasks. Conversely, brain-derived neurotrophic factor (BDNF), whose levels are elevated in response to exercise, is a well-known factor in improving cognitive function. Therefore, the aim of our study was to investigate whether the exercise under hypoxic conditions affects psychomotor performance. For this purpose, 11 healthy young athletes performed a graded cycloergometer exercise test to volitional exhaustion under normoxia and acute mild hypoxia (FiO2 = 14.7%). Before, immediately after exercise and after a period of recovery, choice reaction time (CRT) and number of correct reactions (NCR) in relation to changes in serum BDNF were examined. Additionally, other selected factors which may modify BDNF production, i.e., cortisol (C), nitrite, catecholamines (adrenalin-A, noradrenaline-NA, dopamine-DA, serotonin-5-HT) and endothelin-1 (ET-1), were also measured. Exercise in hypoxic conditions extended CRT by 13.8% (p < 0.01) and decreased NCR (by 11.5%) compared to rest (p < 0.05). During maximal workload, NCR was lower by 9% in hypoxia compared to normoxia (p < 0.05). BDNF increased immediately after exercise in normoxia (by 29.3%; p < 0.01), as well as in hypoxia (by 50.0%; p < 0.001). There were no differences in BDNF between normoxia and hypoxia. Considering the fact that similar levels of BDNF were seen in both conditions but cognitive performance was suppressed in hypoxia, acute elevation of BDNF did not compensate for hypoxia-induced cognition impairment. Moreover, neither potentially negative effects of C nor positive effects of A, DA and NO on the brain were observed in our study.

Role of brain-derived neurotrophic factor in appetite control / Rola neurotroficznego czynnika pochodzenia mózgowego w kontroli laknienia.

It has been found that in brain areas responsible for controlling appetite brain-derived neurotrophic factor (BDNF) and TrkB receptor expression are also present. In addition to involvement in neurogenesis, neuroprotection and synaptic plasticity, BDNF has anorexigenic activity. Decreasing of BDNF levels in the brain causes uncontrolled food intake, in turn, administration of BDNF to the central nervous system (CNS) leads to weight loss in animals. BDNF may participate with other factors such as leptin, insulin, cholecystokinin or corticotropin in the regulation of food intake. In addition, BDNF can affect glucose metabolism. It was found that peripheral BDNF level is lower in anorexia compared to healthy people. Moreover, BDNF levels tend to return to basal value when body weight normalizes. The mutation in the BDNF gene could also be important in the pathogenesis of obesity, although data on the blood concentration of this neurotrophin in obese are ambiguous.

Comparison of the effect of intermittent hypoxic training vs. the live high, train low strategy on aerobic capacity and sports performance in cyclists in normoxia.

The aim of the study was to compare the effect of intermittent hypoxic training (IHT) and the live high, train low strategy on aerobic capacity and sports performance in off-road cyclists in normoxia. Thirty off-road cyclists were randomized to three groups and subjected to 4-week training routines. The participants from the first experimental group were exposed to normobaric hypoxia conditions (FiO2 = 16.3%) at rest and during sleep (G-LH-TL; n=10; age: 20.5 ± 2.9 years; body height 1.81 ± 0.04 m; body mass: 69.6 ± 3.9 kg). Training in this group was performed under normoxic conditions. In the second experimental group, study participants followed an intermittent hypoxic training (IHT, three sessions per week, FiO2 = 16.3%) routine (G-IHT; n=10; age: 20.7 ± 3.1 years; body height 1.78 ± 0.05 m; body mass: 67.5 ± 5.6 kg). Exercise intensity was adjusted based on the lactate threshold (LT) load determined in hypoxia. The control group lived and trained under normoxic conditions (G-C; n=10; age: 21.8 ± 4.0 years; body height 1.78 ± 0.03 m; body mass: 68.1 ± 4.7 kg; body fat content: 8.4 ± 2.4%). The evaluations included two research series (S1, S2). Between S1 and S2, athletes from all groups followed a similar training programme for 4 weeks. In each research series a graded ergocycle test was performed in order to measure VO2max and determine the LT and a simulated 30 km individual time trial. Significant (p<0.05) improvements in VO2max, VO2LT, WRmax and WRLT were observed in the G-IHT (by 3.5%, 9.1%, 6.7% and 7.7% respectively) and G-LH-TL groups (by 4.8%, 6.7%, 5.9% and 4.8% respectively). Sports performance (TT) was also improved (p<0.01) in both groups by 3.6% in G-LH-TL and 2.5% in G-IHT. Significant changes (p<0.05) in serum EPO levels and haematological variables (increases in RBC, HGB, HCT and reticulocyte percentage) were observed only in G-LH-TL. Normobaric hypoxia has been demonstrated to be an effective ergogenic aid that can enhance the exercise capacity of cyclists in normoxia. Both LH-TL and IHT lead to improvements in aerobic capacity. The adaptations induced by both approaches are likely to be caused by different mechanisms. The evaluations included two research series (S1, S2). Between S1 and S2, athletes from all groups followed a similar training programme for 4 weeks. In each research series a graded ergocycle exercise test was performed in order to measure VO2max and determine the lactate threshold as well as a simulated 30 km individual time trial.

The effects of hypobaric hypoxia on erythropoiesis, maximal oxygen uptake and energy cost of exercise under normoxia in elite biathletes.

The aim of the present study was to evaluate the effects of 3 weeks altitude training according to the HiHiLo (live high-base train high-interval train low) procedure as described by Chapman et al. (1998), on erythropoiesis, maximal oxygen uptake and energy cost of exercise under normoxia in elite biathletes. Fifteen male elite biathletes randomly divided into an experimental (H) group (n = 7; age 27.1 ± 4.6 years; maximal oxygen uptake (VO2max) 66.9 ± 3.3 ml·kg(-1)·min(-1); body height (BH) 1.81 ± 0.06 m; body mass (BM) 73.1 ± 5.4kg), and a control (C) group (n = 8; age 23.2 ± 0.9 years; VO2max 68.2 ± 4.1 ml·kg(-1)·min(-1); BH 1.75 ± 0.03 m; BM 63.1 ± 1.5 kg) took part in the study. The H group stayed for 3 weeks at an altitude of 2015 m and performed endurance training on skis four times per week at 3000 m. Additionally, the training protocol included three high-intensity interval sessions at an altitude of 1000 m. The C group followed the same training protocol with skirollers in normoxia at an altitude of 600 m. The HiHiLo protocol applied in our study did not change VO2max or maximal workload (WRmax) significantly during the incremental treadmill test in group H. However, the energy cost for selected submaximal workloads in group H was significantly (p < 0.01) reduced compared to group C (-5.7%, -4.4%, -6% vs. -3.5%, -2.1%, -2.4%). Also a significant (p < 0.001) increase in serum EPO levels during the first two weeks of HiHiLo training at 2015 m was observed, associated with a significant (p < 0.05) increase in hemoglobin mass, number of erythrocytes, hematocrit value and percent of reticulocytes compared with initial values (by 6.4%, 5%, 4.6% and 16,6%, respectively). In group C, changes in these variables were not observed. These positive changes observed in our study led to a conclusion that the HiHiLo training method could improve endurance in normoxia, since most of the biathlon competitions are performed at submaximal intensities. Key pointsThe observed results suggests that the 3-weeks HiHiLo protocol is an effective training means for improving energy cost during submaximal exercise at sea level.The 3-weeks HiHiLo protocol increased the rate of erythropoiesis and improved most haematological variables.However, the positive changes in the athletes haematological variables after the HiHiLo protocol did not contribute to the improvement of VO2max values.

Sports Heart Monitors as Reliable Diagnostic Tools for Training Control and Detecting Arrhythmias in Professional and Leisure-Time Endurance Athletes: An Expert Consensus Statement.

There are countless types of portable heart rate monitoring medical devices used variously by leisure-time exercisers, professional athletes, and chronically ill patients. Almost all the currently used heart rate monitors are capable of detecting arrhythmias, but this feature is not widely known or used among their millions of consumers. The aims of this paper were as follows: (1) to analyze the currently available sports heart rate monitors and assess their advantages and disadvantage in terms of heart rate and rhythm monitoring in endurance athletes; (2) to discuss what types of currently available commercial heart rate monitors are most convenient/adjustable to the needs of different consumers (including occasionally physically active adults and cardiac patients), bearing in mind the potential health risks, especially heart rhythm disturbances connected with endurance training; (3) to suggest a set of "optimal" design features for next-generation smart wearable devices based on the consensus opinion of an expert panel of athletes, coaches, and sports medicine doctors. Ninety-two experts aged 20 years and over, involved in endurance sports on a daily basis, were invited to participate in consensus-building discussions, including 56 long-distance runners, 18 cyclists, nine coaches, and nine physicians (sports medicine specialists, cardiologists, and family medicine doctors). The overall consensus endorsed by these experts indicates that the "optimal" sports heart rate monitor should be a one-piece device of the smartwatch type (with two or more electrodes), with integrated smartphone features, and able to collect and continually transmit data without exhibiting artifacts. It should continuously record at least a single-lead electrocardiography, send an alert after an unexpected fall, be of reasonable weight, come at an affordable price, and be user friendly.

Regular endurance training is among the key factors positively influencing human health. However, there are also many reports describing sudden cardiac fatalities and other serious health problems related to strenuous exercise. Millions of professional and leisure-time athletes worldwide use various digital heart rate monitors to keep track of their training volume, intensity, energy expenditure, running or cycling speed. Nevertheless, currently available heart rate monitors are not tailored to all the specific needs of their users. Moreover, they are not constructed to keep better track of important health functions and thereby improve the safety of endurance training. This paper presents a set of consensus statements developed by a panel of expert heart rate monitor users (endurance athletes, their physicians, and coaches) from three countries. In the panel's view, the "optimal" heart rate monitor should improve users' safety during exercise by providing more reliable medical data informative of potential health risks. A specific set of features of the proposed "optimal" digital heart rate monitor was identified and accepted by the panel of experts. Based on the consensus statements and the available literature, the authors propose next-generation portable devices for use by professional and ambitious leisure-time endurance athletes or even by cardiac patients involved in exercise training (a design called the "Gajda Watch" after the surname of two of the panel organizers/paper authors). One of the biggest challenges is dealing with artifacts and avoiding false information. This consensus document may also be helpful for manufacturers of heart rate monitors seeking new solutions for the sports and medical community.

Metabolic responses to a 48-h ultra-marathon run in middle-aged male amateur runners.

PURPOSE: To evaluate ongoing metabolic changes during a 48-h competitive run and a 48-h recovery period, with focus on potential health risks exemplified by heart and skeletal muscle damage biomarkers and oxidative stress-related indices. METHODS: Blood samples were taken before the race, after 12, 24, and 48 h of running, and after 24 and 48 h of recovery from male amateur runners (N = 7, age 35-59 years, VO2max mean ± SD 57.0 ± 4.0 ml kg(-1) min(-1), total distance covered 183-320 km). The samples were analyzed for morphology, acid-base and electrolyte balance, iron status, lipid profile, interleukin-6, high-sensitivity C-reactive protein, N-terminal pro-brain-type natriuretic peptide, high-sensitivity cardiac troponin T, non-enzymatic antioxidants, activities of selected enzymes including antioxidant enzymes, and total antioxidant status. RESULTS: The sustained ultra-endurance run caused hypocapnic alkalosis with slight hyperkalemia and hypocalcemia, but no hyponatremia. Blood biochemistry showed severe muscle but not liver damage, and an acute inflammatory response. These effects were evidenced by leukocytosis, several fold rises in interleukin-6 and high sensitivity C-reactive protein, extreme elevations in serum levels of muscle enzymes, and marked increases in cardiac biomarker levels. Most of the changes dissolved during the 48 h post-race recovery. Neither the iron pool, nor erythropoiesis, nor pro-oxidant/antioxidant balance were substantially affected. CONCLUSIONS: The changes consequent on the ultra-endurance run do not pose a serious health risk in men who begin their endeavor with ultra-endurance running in mid-life. There is some circumstantial evidence that hyperventilatory hypocapnia may modulate inflammatory response by stimulating the release of interleukin-6 from working skeletal muscles.

The Impact of Acute Mild Normobaric Hypoxia and a Single Bout of Exercise to Volitional Exhaustion on Cognitive Performance in Endurance and Strength-Trained Athletes: The role of BDNF, EP-1, Catecholamines and Lactate.

The aim of the study was to examine whether a single bout of exercise to volitional exhaustion, performed under moderate normobaric hypoxia (H), would affect psychomotor performance (PP) in differently trained athletes. For this purpose, ten strength-trained (S) athletes, ten endurance-trained (E) athletes and ten healthy men leading a sedentary lifestyle as a control (C) group performed voluntarily two graded exercise tests until volitional exhaustion (EVE) under normoxia (N) and H (FiO2 = 14.7%). We measured the peripheral level of the brain derived neurotrophic factor (BDNF), choice reaction time (CRT) and the number of correct reactions (NCR) as indices of PP. Psychomotor tests were performed at rest, immediately after the EVE and 3 minutes after the EVE. Venous blood samples were collected at rest, immediately after cessation of each EVE, and 1 h after each EVE. The results showed that the EVE significantly (p < 0.05) impaired CRT under N and H, and NCR under H only in the E group. The higher WRmax in the E compared to the S and C groups was associated with a significant (p < 0.005) increase in adrenaline (A) and noradrenaline (NA). There were no significant differences between conditions (N vs. H) in the BDNF at rest and after exercise. The EVE impaired cognitive function only in the E group; higher involvement of the sympathetic nervous system, A and NA may also play a role in this phenomenon. Therefore, it can be concluded that exposure to H did not have a negative impact on CRT or NCR. Moreover, BDNF did not improve cognitive function.

The Effects of Six-Gram D-Aspartic Acid Supplementation on the Testosterone, Cortisol, and Hematological Responses of Male Boxers Subjected to 11 Days of Nocturnal Exposure to Normobaric Hypoxia.

The aim of this study was to evaluate the effects of D-aspartic acid (DAA) supplementation during a simulated altitude protocol on the hormonal and hematological responses in athletes. We hypothesized that DAA supplementation would contribute to an increase in the luteinizing hormone (LH), free, and testosterone and a greater increase in hematological variables. Sixteen male boxers participated; they were randomly assigned to an experimental group (DAA) or a control group (C) and underwent 14 days of supplementation, 6 g/day of DAA. Both DAA and C participants were exposed to normobaric hypoxia (FiO2 = 15.5%; 2500 m) for 10-12 h a day over a period of 11 days. The results showed that DAA had no significant effect on resting, LH, or the testosterone/cortisol ratio during the training camp. Hypoxic exposure significantly (p < 0.05) increased red blood cell and reticulocyte counts as well as hemoglobin and hematocrit concentrations in both groups, but DAA had no significant effect on these changes. In conclusion, we found that DAA supplementation at a dose of 6 g/day for 14 days does not affect the testosterone, cortisol, or hematological responses of athletes during.

Hepcidin and erythroferrone response to 3 weeks of exposure to normobaric hypoxia at rest in trained cyclists.

Purpose: The effectiveness of altitude training on haematological adaptations is largely dependent on iron metabolism. Hepcidin and erythroferrone (ERFE) are key iron-regulating hormones, yet their response to altitude training is poorly understood. The aim of this study was to analyze changes in hepcidin and ERFE under the influence of 3 weeks of the Live High-Train Low (LH-TL) method. Methods: Twenty male trained cyclists completed a 3-week training program under normoxic conditions (NORM) or with passive exposure to normobaric hypoxia (LH-TL; FiO2 = 16.5%, ∼2000 m; 11-12 h/day). Hepcidin, ERFE, hypoxia inducible factor-2 (HIF-2), ferroportin (Fpn), erythropoietin (EPO), serum iron (Fe) and hematological variables were assessed at baseline (S1), then immediately after (S2) and 3 days after (S3) intervention. Results: In the LH-TL group, hepcidin decreased by 13.0% (p < 0.001) in S2 and remained at a reduced level in S3. ERFE decreased by 28.7% (p < 0.05) in S2 and returned to baseline in S3. HIF-2α decreased gradually, being lower by 25.3% (p < 0.05) in S3. Fpn decreased between S1 and S2 by 18.9% (p < 0.01) and remained lower during S3 (p < 0.01). In the NORM group, in turn, hepcidin levels increased gradually, being higher by 73.9% (p < 0.05) in S3 compared to S1. No statistically significant differences in EPO were observed in both groups. Conclusion: Three weeks of LH-TL suppresses resting hepcidin and ERFE levels in endurance athletes. We found no association between hepcidin and ERFE after LH-TL. Probably, ERFE is not the only factor that suppresses hepcidin expression in response to moderate hypoxia, especially in later stages of hepcidin downregulation. With the cessation of hypoxia, favorable conditions for increasing the availability of iron cease.

Acute metabolic responses to a 24-h ultra-marathon race in male amateur runners.

The study was conducted to evaluate the metabolic responses to a 24 h ultra-endurance race in male runners. Paired venous and capillary blood samples from 14 athletes (mean age 43.0 ± 10.8 years, body weight 64.3 ± 7.2 kg, VO(2max) 57.8 ± 6.1 ml kg(-1) min(-1)), taken 3 h before the run, after completing the marathon distance (42.195 km), after 12 h, and at the finish of the race, were analyzed for blood morphology, acid-base balance and electrolytes, lipid profile, interleukin-6 (IL-6), high-sensitivity C-reactive protein (hsCRP), and serum enzyme activities. Mean distance covered during the race was 168.5 ± 23.1 km (range 125.2-218.5 km). Prolonged ultra-endurance exercise triggered immune and inflammatory responses, as evidenced by a twofold increase in total leukocyte count with neutrophils and monocytes as main contributors, nearly 30-fold increase in serum IL-6 and over 20-fold rise in hsCRP. A progressive exponential increase in mean creatine kinase activity up to the level 70-fold higher than the respective pre-race value, a several fold rise in serum activities of aspartate aminotransferase and alanine aminotransferase, and a fairly stable serum γ-glutamyl transferase level, were indicative of muscle, but not of liver damage. With duration of exercise, there was a progressive development of hyperventilation-induced hypocapnic alkalosis, and a marked alteration in substrate utilization towards fat oxidation to maintain blood glucose homeostasis. The results of this study may imply that progressive decline in partial CO(2) pressure (hypocapnia) that develops during prolonged exercise may contribute to increased interleukin-6 production.

Application of regression and neural models to predict competitive swimming performance.

This research problem was indirectly but closely connected with the optimization of an athlete-selection process, based on predictions viewed as determinants of future successes. The research project involved a group of 249 competitive swimmers (age 12 yr., SD = 0.5) who trained and competed for four years. Measures involving fitness (e.g., lung capacity), strength (e.g., standing long jump), swimming technique (turn, glide, distance per stroke cycle), anthropometric variables (e.g., hand and foot size), as well as specific swimming measures (speeds in particular distances), were used. The participants (n = 189) trained from May 2008 to May 2009, which involved five days of swimming workouts per week, and three additional 45-min. sessions devoted to measurements necessary for this study. In June 2009, data from two groups of 30 swimmers each (n = 60) were used to identify predictor variables. Models were then constructed from these variables to predict final swimming performance in the 50 meter and 800 meter crawl events. Nonlinear regression models and neural models were built for the dependent variable of sport results (performance at 50m and 800m). In May 2010, the swimmers' actual race times for these events were compared to the predictions created a year prior to the beginning of the experiment. Results for the nonlinear regression models and perceptron networks structured as 8-4-1 and 4-3-1 indicated that the neural models overall more accurately predicted final swimming performance from initial training, strength, fitness, and body measurements. Differences in the sum of absolute error values were 4:11.96 (n = 30 for 800m) and 20.39 (n = 30 for 50m), for models structured as 8-4-1 and 4-3-1, respectively, with the neural models being more accurate. It seems possible that such models can be used to predict future performance, as well as in the process of recruiting athletes for specific styles and distances in swimming.

Effects of Short-Term Phosphate Loading on Aerobic Capacity under Acute Hypoxia in Cyclists: A Randomized, Placebo-Controlled, Crossover Study.

The aim of this study was to evaluate the effects of sodium phosphate (SP) supplementation on aerobic capacity in hypoxia. Twenty-four trained male cyclists received SP (50 mg·kg-1 of FFM/day) or placebo for six days in a randomized, crossover study, with a three-week washout period between supplementation phases. Before and after each supplementation phase, the subjects performed an incremental exercise test to exhaustion in hypoxia (FiO2 = 16%). Additionally, the levels of 2,3-diphosphoglycerate (2,3-DPG), hypoxia-inducible factor 1 alpha (HIF-1α), inorganic phosphate (Pi), calcium (Ca), parathyroid hormone (PTH) and acid-base balance were determined. The results showed that phosphate loading significantly increased the Pi level by 9.0%, whereas 2,3-DPG levels, hemoglobin oxygen affinity, buffering capacity and myocardial efficiency remained unchanged. The aerobic capacity in hypoxia was not improved following SP. Additionally, our data revealed high inter-individual variability in response to SP. Therefore, the participants were grouped as Responders and Non-Responders. In the Responders, a significant increase in aerobic performance in the range of 3-5% was observed. In conclusion, SP supplementation is not an ergogenic aid for aerobic capacity in hypoxia. However, in certain individuals, some benefits can be expected, but mainly in athletes with less training-induced central and/or peripheral adaptation.

Chronic Exposure to Normobaric Hypoxia Increases Testosterone Levels and Testosterone/Cortisol Ratio in Cyclists.

The aim of this study was to analyze the effects of the "live high, train low" method (LH−TL) and intermittent hypoxic training (IHT) on testosterone (T) and cortisol (C) levels in cyclists. Thirty cyclists participated in the experiment. The LH−TL group (n = 10) was exposed to normobaric hypoxia (FiO2 = 16.3%) for 11−12 h a day and trained in normoxia for 3 weeks. In the IHT group (n = 10), participants followed the IHT routine three times a week for 3 weeks in normobaric hypoxia (FiO2 = 16.3%). The control group (N; n = 10) followed the same training protocol in normoxia. The LH−TL training was found to significantly increase (p < 0.05) T levels and the testosterone/cortisol (T/C) ratio during the experiment. The area under the curve (AUC) calculated for T levels over 4 weeks was significantly (p < 0.05) higher in the LH−TL group, by 25.6%, compared to the N group. The results also indicated a significant correlation (r = 0.53; p < 0.05) between AUC for T levels over 4 weeks and ∆ values of hemoglobin (HGB) in the LH−TL group. Overall, the findings show that LH−TL training at a moderate simulated altitude contributes to an increase in T levels and T/C ratio in athletes, which is a beneficial change stimulating anabolic processes and erythropoiesis.

Effect of Normobaric Hypoxia on Alterations in Redox Homeostasis, Nitrosative Stress, Inflammation, and Lysosomal Function following Acute Physical Exercise.

Hypoxia is a recognized inducer of oxidative stress during prolonged physical activity. Nevertheless, previous studies have not systematically examined the effects of normoxia and hypoxia during acute physical exercise. The study is aimed at evaluating the relationship between enzymatic and nonenzymatic antioxidant barrier, total antioxidant/oxidant status, oxidative and nitrosative damage, inflammation, and lysosomal function in different acute exercise protocols under normoxia and hypoxia. Fifteen competitive athletes were recruited for the study. They were subjected to two types of acute cycling exercise with different intensities and durations: graded exercise until exhaustion (GE) and simulated 30 km individual time trial (TT). Both exercise protocols were performed under normoxic and hypoxic (FiO2 = 16.5%) conditions. The number of subjects was determined based on our previous experiment, assuming the test power = 0.8 and α = 0.05. We demonstrated enhanced enzymatic antioxidant systems during hypoxic exercise (GE: ↑ catalase (CAT), ↑ superoxide dismutase; TT: ↑ CAT) with a concomitant decrease in plasma reduced glutathione. In athletes exercising in hypoxia, redox status was shifted in favor of oxidation reactions (GE: ↑ total oxidant status, ↓ redox ratio), leading to increased oxidation/nitration of proteins (GE: ↑ advanced oxidation protein products (AOPP), ↑ ischemia-modified albumin, ↑ 3-nitrotyrosine, ↑ S-nitrosothiols; TT: ↑ AOPP) and lipids (GE: ↑ malondialdehyde). Concentrations of nitric oxide and its metabolites (peroxynitrite) were significantly higher in the plasma of hypoxic exercisers with an associated increase in inflammatory mediators (GE: ↑ myeloperoxidase, ↑ tumor necrosis factor-alpha) and lysosomal exoglycosidase activity (GE: ↑ N-acetyl-ß-hexosaminidase, ↑ ß-glucuronidase). Our study indicates that even a single intensive exercise session disrupts the antioxidant barrier and leads to increased oxidative and nitrosative damage at the systemic level. High-intensity exercise until exhaustion (GE) alters redox homeostasis more than the less intense exercise (TT, near the anaerobic threshold) of longer duration (20.2 ± 1.9 min vs. 61.1 ± 5.4 min-normoxia; 18.0 ± 1.9 min vs. 63.7 ± 3.0 min-hypoxia), while hypoxia significantly exacerbates oxidative stress, inflammation, and lysosomal dysfunction in athletic subjects.

The effects of intermittent hypoxic training on aerobic capacity and endurance performance in cyclists.

The aim of the present study was to evaluate the efficacy of intermittent hypoxic training (IHT) with 95 % of lactate threshold workload (WRLT) on aerobic capacity and endurance performance in well-trained cyclists. Twenty male elite cyclists, randomly divided into a hypoxia (H) group (n=10; age 22 ± 2.7years; VO2max 67.8 ± 2.5 ml·kg(-1)·min(-1); body height (BH) 1.78 ± 0.05 m; body mass (BM) 66.7 ± 5.4kg; fat free mass (FFM) 59.3 ± 5.1kg; fat content (FAT%) 11.3 ± 2.1%), and a control (C) group (n = 10; age 23.5 ± 3. 5years; VO2max 67.7 ± 2.0 ml·kg(-1)·min(-1); BH 1.79 ± 3.2 m; BM 69.2 ± 5.5 kg; FFM 63.6 ± 4.8 kg; FAT% 7.9 ± 1.94 %) took part in the research project. The training program used during the experiment was the same for the both groups. For three weeks, the subjects in H group performed 3 training sessions per week in normobaric hypoxia environment (IHT - O2 = 15. 2%). During the elemental core of the IHT session, the intensity was set at 95% WRLT for 30-min in 1(st) microcycle, 35-min in 2(nd) microcycle and 40-min in 3(rd) microcycle. The same training procedure was provided in C group, yet the intensity of the main sessions were set at 100% WRLT in the normoxia environment. The results indicate a significant (p < 0.05) increase in VO2max,VO2LT, WRmax, WRLT and change in lactate concentration (∆LA) during incremental test in H group. Also a significant (p < 0.05) decrease in time of the time trial was seen, associated with a significant increase (p < 0.05) in average generated power (Pavg) and average speed (Vavg) during the time trial. The intermittent hypoxic training (IHT) applied in this research did not significantly affect the hematological variables considered: number of erythrocytes (RBC), hemoglobin concentration (HGB) and haematocrit value (HCT). Significant blood value increases (p < 0.05) were only observed in MCV in H group. This data suggests that intermittent hypoxic training at lactate threshold intensity and medium duration (30-40min) is an effective training means for improving aerobic capacity and endurance performance at sea level. Key pointsThe efficacy of the intermittent hypoxic training is mostly dependent on volume and intensity of exercise in the hypoxic environment.The observed results suggests that intermittent hypoxic training at lactate threshold intensity and medium duration (30-40min) is an effective training means for improving aerobic capacity and endurance performance at sea level.

The Effects of Sodium Phosphate Supplementation on the Cardiorespiratory System and Gross Efficiency during Exercise under Hypoxia in Male Cyclists: A Randomized, Placebo-Controlled, Cross-Over Study.

The main aim of this study was to evaluate the effects of six days of tri-sodium phosphate (SP) supplementation on the cardiorespiratory system and gross efficiency (GE) during exercise under hypoxia in cyclists. Twenty trained male cyclists received SP (50 mg·kg-1 of fat-free mass/day) or placebo for six days in a randomized, cross-over study, with a three-week washout period between supplementation phases. Before and after each supplementation phase, the subjects performed an incremental exercise test to exhaustion under normobaric hypoxia (FiO2 = 16%, ~2500 m). It was observed that short-term SP supplementation led to a decrease in heart rate, an increase in stroke volume, and an improvement in oxygen pulse (VO2/HR) during low and moderate-intensity exercise under hypoxia. These changes were accompanied by an increase in the serum inorganic phosphate level by 8.7% (p < 0.05). No significant changes were observed in serum calcium levels. GE at a given workload did not change significantly after SP supplementation. These results indicated that SP promotes improvements in the efficiency of the cardiorespiratory system during exercise in a hypoxic environment. Thus, SP supplementation may be beneficial for endurance exercise in hypoxia.

Exposure to Normobaric Hypoxia Combined with a Mixed Diet Contributes to Improvement in Lipid Profile in Trained Cyclists.

This study aimed to analyze the effects of live high-train low method (LH-TL) and intermittent hypoxic training (IHT) with a controlled mixed diet on lipid profile in cyclists. Thirty trained male cyclists at a national level with at least six years of training experience participated in the study. The LH-TL group was exposed to hypoxia (FiO2 = 16.5%) for 11-12 h a day and trained under normoxia for 3 weeks. In the IHT group, participants followed the IHT routine three times a week under hypoxia (FiO2 = 16.5%) at lactate threshold intensity. The control group (N) lived and trained under normoxia. The results showed that the 3-week LH-TL method significantly improved all lipid profile variables. The LH-TL group showed a significant increase in HDL-C by 9.0% and a decrease in total cholesterol (TC) by 9.2%, LDL-C by 18.2%, and triglycerides (TG) by 27.6%. There were no significant changes in lipid profiles in the IHT and N groups. ∆TG and ∆TC were significantly higher in the LH-TL group compared to the N group. In conclusion, hypoxic conditions combined with a mixed diet can induce beneficial changes in lipid profile even in highly trained athletes. The effectiveness of the hypoxic stimulus is closely related to the hypoxic training method.

Red Blood Cell 2,3-Diphosphoglycerate Decreases in Response to a 30 km Time Trial Under Hypoxia in Cyclists.

Red blood cell 2,3-diphosphoglycerate (2,3-DPG) is one of the factors of rightward-shifted oxygen dissociation curves and decrease of Hb-O2 affinity. The reduction of Hb-O2 affinity is beneficial to O2 unloading at the tissue level. In the current literature, there are no studies about the changes in 2,3-DPG level following acute exercise in moderate hypoxia in athletes. For this reason, the aim of this study was to analyze the effect of prolonged intense exercise under normoxic and hypoxic conditions on 2,3-DPG level in cyclists. Fourteen male trained cyclists performed a simulation of a 30 km time trial (TT) in normoxia and normobaric hypoxia (FiO2 = 16.5%, ~2,000 m). During the TT, the following variables were measured: power, blood oxygen saturation (SpO2), and heart rate (HR). Before and immediately after exercise, the blood level of 2,3-DPG and acid-base equilibrium were determined. The results showed that the mean SpO2 during TT in hypoxia was 8% lower than in normoxia. The reduction of SpO2 in hypoxia resulted in a decrease of average power by 9.6% (p < 0.001) and an increase in the 30 km TT completion time by 3.8% (p < 0.01) compared to normoxia. The exercise in hypoxia caused a significant (p < 0.001) decrease in 2,3-DPG level by 17.6%. After exercise in normoxia, a downward trend of 2,3-DPG level was also observed, but this effect was not statistically significant. The analysis also revealed that changes of acid-base balance were significantly larger (p < 0.05) after exercise in hypoxia than in normoxia. In conclusion, intense exercise in hypoxic conditions leads to a decrease in 2,3-DPG concentration, primarily due to exercise-induced acidosis.