Increased hemoglobin mass and VO2max with 10 h nightly simulated altitude at 3000 m

Impact of Altitude Training on Athletes' Aerobic Capacity: A Systematic Review and Meta-Analysis

Purpose: This study systematically evaluated the effects of altitude training on athletes' aerobic capacity, focusing on optimal training modalities and intervention durations. Methods: Eight databases (CNKI, CSPD, PubMed, Ovid Medline, ProQuest, Cochrane Library, Embase, and Scopus) were searched for randomized controlled trials on altitude training and aerobic capacity following PRISMA guidelines, covering publications up to 15 October 2024. The risk of bias was assessed using Cochrane tools, and a meta-analysis was conducted using Review Manager 5.4 with a random-effects model. Sensitivity and subgroup analyses were performed to identify heterogeneity and influencing factors. Results: Thirteen studies involving 276 participants (aged 18-35) were included. Meta-analysis revealed that compared to low-altitude training, altitude training significantly increased hemoglobin (SMD = 0.7, 95% CI: 0.27-1.13, p = 0.03) and hemoglobin mass (SMD = 0.49, 95% CI: 0.1-0.89, p = 0.16) but had no significant effect on maximal oxygen uptake (SMD = -0.13, 95% CI: -1.21-0.96, p = 0.68). Altitude training also improved performance in trial tests (SMD = -28.73, 95% CI: -58.69-1.23, p = 0.002). Sensitivity analysis confirmed the robustness of hemoglobin and trial test results. Subgroup analysis showed that the "live high, train high" (LHTH) approach and interventions lasting longer than three weeks were most effective in enhancing aerobic capacity. Conclusions: Altitude training improves athletes' aerobic capacity by enhancing hematological indicators and trial test performance, though its impact on maximal oxygen uptake is minimal. LHTH and interventions exceeding three weeks yield superior outcomes. However, the findings are limited by the number and quality of the available studies.

Evaluating the Therapeutic Potential of Exercise in Hypoxia and Low-Carbohydrate, High-Fat Diet in Managing Hypertension in Elderly Type 2 Diabetes Patients: A Novel Intervention Approach

BACKGROUND/OBJECTIVES

Type 2 diabetes mellitus (T2DM) is a chronic condition marked by hyperglycemia, which can affect metabolic, vascular, and hematological parameters. A low-carbohydrate, high-fat (LCHF) diet has been shown to improve glycemic control and blood pressure regulation. Exercise in hypoxia (EH) enhances insulin sensitivity, erythropoiesis, and angiogenesis. The combination of LCHF and EH may offer a promising strategy for managing T2DM and hypertension (HTN), although evidence remains limited. This study aimed to assess the effects of an eight-week normobaric EH intervention at 3000 m simulated altitude combined with an LCHF diet on hematological and lipid profiles, inflammation, and blood pressure in older patients with T2DM and HTN.

METHODS

Forty-two diabetic patients with HTN were randomly assigned to three groups: (1) control group (control diet + exercise in normoxia), (2) EH group (control diet + EH), and (3) intervention group (EH+LCHF) Baseline and eight-week measurements included systolic, diastolic, and mean blood pressure (SBP, DBP, MAP), hematological and lipid profiles, and inflammation biomarkers.

RESULTS

Blood pressure decreased after the intervention (p < 0.001), with no significant differences between groups (SBP: p = 0.151; DBP: p = 0.124; MAP: p = 0.18). No differences were observed in lipid profile or C-reactive protein levels (p > 0.05). Mean corpuscular hemoglobin (MCH) increased in the EH group (p = 0.027), while it decreased in the EH+LCHF group (p = 0.046).

CONCLUSIONS

Adding hypoxia or restricting carbohydrates did not provide additional benefits on blood pressure in T2DM patients with HTN. Further elucidation of the mechanisms underlying hematological adaptations is imperative.

TRIAL REGISTRATION NUMBER

NCT05094505.

Carbon monoxide supplementation: evaluating its potential to enhance altitude training effects and cycling performance in elite athletes

Altitude training is a cornerstone for endurance athletes for improving blood variables and performance, with optimal effects observed at ∼2,300-2,500 meters above sea level (m.a.s.l.). However, elite cyclists face challenges such as limited access to such altitudes, inadequate training facilities, and high expenses. To address these issues, a novel method involving daily exposure to carbon monoxide (CO) has been proposed to amplify altitude training adaptations at suboptimal altitudes. Thirty-one male cyclists were assigned to three groups: Live-High Train-High with CO inhalation (LHTHCO), Live-High Train-High (LHTH), and Live-Low Train-Low (LLTL). The LHTHCO group underwent CO inhalation twice daily in the afternoon/evening to elevate carboxyhemoglobin concentration to ∼10%. Hematological variables, in vivo muscle oxidative capacity, and physiological indicators of cycling performance were assessed before and after a 3-week altitude training camp at 2,100 m.a.s.l. LHTHCO demonstrated a larger increase in hemoglobin mass (Hbmass) compared to both LHTH and LLTL. Although there were no statistical differences between LHTHCO and LHTH in submaximal and maximal performance measures, LHTHCO displayed greater improvements in 1-min maximal power output during incremental testing (Wmax), power output at lactate threshold, and maximal oxygen consumption (V̇o2max) compared to LLTL. LHTH demonstrated a larger improvement than LLTL in Wmax and V̇o2max, with no group differences in Hbmass or submaximal measures. Muscle oxidative capacity did not differ between groups. These findings suggest that combining moderate-altitude training with daily CO inhalation promotes hematological adaptations more effectively than moderate altitude alone and enhances cycling performance metrics in cyclists more than sea-level training.NEW & NOTEWORTHY Three weeks of training at moderate altitude with exposure to low doses of CO can significantly enhance hematological adaptations in elite cyclists compared to moderate-altitude training alone. Cycling performance determinants improved more with CO inhalation at moderate altitude compared to sea-level training, whereas there were no differences in submaximal and maximal performance measures compared to moderate-altitude training alone. This study highlights the potential of CO supplementation as an effective adjunct to altitude training regimens.

Physiological and performance effects of live high train low altitude training for elite endurance athletes: A narrative review

Altitude training has become an important training application for athletes due its potential for altering physiology and enhancing performance. This practice is commonly used by athletes, with a popular choice being the live high - train low approach. This model recommends that athletes live at high altitude (1250-3000 m), but train at low altitude or sea-level (0-1200 m). Exposure to altitude often leads to hypoxic stress and in turn stimulates changes in total haemoglobin mass, erythropoietin, and soluble transferrin receptors, which alter further underlying physiology. Through enhanced physiology, improved exercise performance may arise through enhancement of the oxygen transport system which is important for endurance events. Previous investigations into the effects of altitude training on exercise performance have been completed in a range of contexts, including running, cycling, swimming, and triathlon. Often following a LHTL altitude intervention, athletes realise improvements in maximal oxygen consumption capacity, time trial performance and peak power outputs. Although heterogeneity exists among LHTL methodologies, i.e., exposure durations and altitude ranges, we synthesised this data into kilometre hours, and found that the most common hypoxic doses used in LHTL interventions ranged from ∼578-687 km h. As this narrative review demonstrates, there are potential advantages to using altitude training to enhance physiology and improve performance for endurance athletes.

Factors Confounding the Athlete Biological Passport: A Systematic Narrative Review

BACKGROUND

Through longitudinal, individual and adaptive monitoring of blood biomarkers, the haematological module of the athlete biological passport (ABP) has become a valuable tool in anti-doping efforts. The composition of blood as a vector of oxygen in the human body varies in athletes with the influence of multiple intrinsic (genetic) or extrinsic (training or environmental conditions) factors. In this context, it is fundamental to establish a comprehensive understanding of the various causes that may affect blood variables and thereby alter a fair interpretation of ABP profiles.

METHODS

This literature review described the potential factors confounding the ABP to outline influencing factors altering haematological profiles acutely or chronically.

RESULTS

Our investigation confirmed that natural variations in ABP variables appear relatively small, likely-at least in part-because of strong human homeostasis. Furthermore, the significant effects on haematological variations of environmental conditions (e.g. exposure to heat or hypoxia) remain debatable. The current ABP paradigm seems rather robust in view of the existing literature that aims to delineate adaptive individual limits. Nevertheless, its objective sensitivity may be further improved.

CONCLUSIONS

This narrative review contributes to disentangling the numerous confounding factors of the ABP to gather the available scientific evidence and help interpret individual athlete profiles.

Contemporary Periodization of Altitude Training for Elite Endurance Athletes: A Narrative Review

Since the 1960s there has been an escalation in the purposeful utilization of altitude to enhance endurance athletic performance. This has been mirrored by a parallel intensification in research pursuits to elucidate hypoxia-induced adaptive mechanisms and substantiate optimal altitude protocols (e.g., hypoxic dose, duration, timing, and confounding factors such as training load periodization, health status, individual response, and nutritional considerations). The majority of the research and the field-based rationale for altitude has focused on hematological outcomes, where hypoxia causes an increased erythropoietic response resulting in augmented hemoglobin mass. Hypoxia-induced non-hematological adaptations, such as mitochondrial gene expression and enhanced muscle buffering capacity may also impact athletic performance, but research in elite endurance athletes is limited. However, despite significant scientific progress in our understanding of hypobaric hypoxia (natural altitude) and normobaric hypoxia (simulated altitude), elite endurance athletes and coaches still tend to be trailblazers at the coal face of cutting-edge altitude application to optimize individual performance, and they already implement novel altitude training interventions and progressive periodization and monitoring approaches. Published and field-based data strongly suggest that altitude training in elite endurance athletes should follow a long- and short-term periodized approach, integrating exercise training and recovery manipulation, performance peaking, adaptation monitoring, nutritional approaches, and the use of normobaric hypoxia in conjunction with terrestrial altitude. Future research should focus on the long-term effects of accumulated altitude training through repeated exposures, the interactions between altitude and other components of a periodized approach to elite athletic preparation, and the time course of non-hematological hypoxic adaptation and de-adaptation, and the potential differences in exercise-induced altitude adaptations between different modes of exercise.

Hematological status and endurance performance predictors after low altitude training supported by normobaric hypoxia: a double-blind, placebo controlled study

The benefits of altitude/hypoxic training for sea level performance are still under debate. This study examined the effects of low altitude training supported by normobaric hypoxia on hematological status and endurance performance predictors in elite female cyclists. Twenty-two female cyclists trained for 3 weeks at low altitude (<1100 m) and 2 weeks near sea level. During the first 3 weeks, 15 subjects stayed in hypoxic rooms simulating an altitude of 2200 m (+NH group, n = 8) or 1000 m (placebo group, n = 7), and 7 (control group) stayed in regular rooms. Significant increases in total hemoglobin mass (tHb-mass: p = 0.008, p = 0.025), power at 4 mmol·l^-1 lactate (PAT4: p = 0.004, p = 0.005) (in absolute and relative values, respectively) and maximal power (PF: p = 0.034) (in absolute values) were observed. However, these effects were not associated with normobaric hypoxia. Changes in tHb-mass were not associated with initial concentrations of ferritin or transferrin receptor, whereas changes in relative tHb-mass (r = -0.53, p = 0.012), PF (r = -0.53, p = 0.01) and PAT4 (r = -0.65, p = 0.001) were inversely correlated with initial values. Changes in tHb-mass and PAT4 were positively correlated (r = 0.50, p = 0.017; r = 0.47, p = 0.028). Regardless of normobaric hypoxia application, low altitude training followed by sea-level training might improve hematological status in elite female cyclists, especially with relatively low initial values of tHb-mass, which could translate into enhanced endurance performance.

The Effects of Altitude Training on Erythropoietic Response and Hematological Variables in Adult Athletes: A Narrative Review

Background: One of the goals of altitude training is to increase blood oxygen-carrying capacity in order to improve sea-level endurance performance in athletes. The elevated erythropoietin (EPO) production in hypoxia is a key factor in the achievement of enhanced hematological variables. The level of the EPO increase and acceleration of erythropoiesis depend on the duration of exposure and degree of hypoxia. Furthermore, many other factors may affect the hematological response to altitude training.

Aim: The purpose of this narrative review was to: (1) analyze the kinetics of EPO and hematological variables during and after altitude training; (2) summarize the current state of knowledge about the possible causes of individual or cohort differences in EPO and hematological response to altitude training; (3) formulate practical guidelines for athletes to improve the efficiency of altitude training.

Methods: A narrative review was performed following an electronic search of the databases PubMed/MEDLINE and SPORTDiscus via EBSCO for all English-language articles published between 1997 and 2017.

Results: Complete unification of results from studies on EPO kinetics was difficult due to different time and frequency of blood sampling by different researchers during and after altitude training, but the data presented in the reviewed literature allowed us to detect certain trends. The results of the reviewed studies were divergent and indicated either increase or no change of hematological variables following altitude training. Factors that may affect the hematological response to altitude training include hypoxic dose, training content, training background of athletes, and/or individual variability of EPO production.

Conclusions: Despite the potential benefits arising from altitude training, its effectiveness in improving hematological variables is still debatable. Further research and better understanding of factors influencing the response to altitude, as well as factors affecting the suitable measurement and interpretation of study results, are needed.

Individual hemoglobin mass response to normobaric and hypobaric "live high-train low": A one-year crossover study

The purpose of this research was to compare individual hemoglobin mass (Hb_mass) changes following a live high-train low (LHTL) altitude training camp under either normobaric hypoxia (NH) or hypobaric hypoxia (HH) conditions in endurance athletes. In a crossover design with a one-year washout, 15 male triathletes randomly performed two 18-day LHTL training camps in either HH or NH. All athletes slept at 2,250 meters and trained at altitudes <1,200 meters. Hb_mass was measured in duplicate with the optimized carbon monoxide rebreathing method before (pre) and immediately after (post) each 18-day training camp. Hb_mass increased similarly in HH (916-957 g, 4.5 ± 2.2%, P < 0.001) and in NH (918-953 g, 3.8 ± 2.6%, P < 0.001). Hb_mass changes did not differ between HH and NH (P = 0.42). There was substantial interindividual variability among subjects to both interventions (i.e., individual responsiveness or the individual variation in the response to an intervention free of technical noise): 0.9% in HH and 1.7% in NH. However, a correlation between intraindividual ΔHb_mass changes (%) in HH and in NH (r = 0.52, P = 0.048) was observed. HH and NH evoked similar mean Hb_mass increases following LHTL. Among the mean Hb_mass changes, there was a notable variation in individual Hb_mass response that tended to be reproducible.NEW & NOTEWORTHY This is the first study to compare individual hemoglobin mass (Hb_mass) response to normobaric and hypobaric live high-train low using a same-subject crossover design. The main findings indicate that hypobaric and normobaric hypoxia evoked a similar mean increase in Hb_mass following 18 days of live high-train low. Notable variability and reproducibility in individual Hb_mass responses between athletes was observed, indicating the importance of evaluating individual Hb_mass response to altitude training.

Similar Hemoglobin Mass Response in Hypobaric and Normobaric Hypoxia in Athletes

PURPOSE

To compare hemoglobin mass (Hb(mass)) changes during an 18-d live high-train low (LHTL) altitude training camp in normobaric hypoxia (NH) and hypobaric hypoxia (HH).

METHODS

Twenty-eight well-trained male triathletes were split into three groups (NH: n = 10, HH: n = 11, control [CON]: n = 7) and participated in an 18-d LHTL camp. NH and HH slept at 2250 m, whereas CON slept, and all groups trained at altitudes <1200 m. Hb(mass) was measured in duplicate with the optimized carbon monoxide rebreathing method before (pre-), immediately after (post-) (hypoxic dose: 316 vs 238 h for HH and NH), and at day 13 in HH (230 h, hypoxic dose matched to 18-d NH). Running (3-km run) and cycling (incremental cycling test) performances were measured pre and post.

RESULTS

Hb(mass) increased similar in HH (+4.4%, P < 0.001 at day 13; +4.5%, P < 0.001 at day 18) and NH (+4.1%, P < 0.001) compared with CON (+1.9%, P = 0.08). There was a wide variability in individual Hb(mass) responses in HH (-0.1% to +10.6%) and NH (-1.4% to +7.7%). Postrunning time decreased in HH (-3.9%, P < 0.001), NH (-3.3%, P < 0.001), and CON (-2.1%, P = 0.03), whereas cycling performance changed nonsignificantly in HH and NH (+2.4%, P > 0.08) and remained unchanged in CON (+0.2%, P = 0.89).

CONCLUSION

HH and NH evoked similar Hb(mass) increases for the same hypoxic dose and after 18-d LHTL. The wide variability in individual Hb(mass) responses in HH and NH emphasizes the importance of individual Hb(mass) evaluation of altitude training.

Erythropoietin directly stimulates osteoclast precursors and induces bone loss

Erythropoietin (EPO) primarily regulates red blood cell formation, and EPO serum levels are increased on hypoxic stress (e.g., anemia and altitude). In addition to anemia, recent discoveries suggest new therapeutic indications for EPO, unrelated to erythropoiesis. We investigated the skeletal role of EPO using several models of overexpression (Tg6 mice) and EPO administration (intermittent/continuous, high/low doses) in adult C57Bl6 female mice. Using microcomputed tomography, histology, and serum markers, we found that EPO induced a 32%-61% trabecular bone loss caused by increased bone resorption (+60%-88% osteoclast number) and reduced bone formation rate (-19 to -74%; P < 0.05 throughout). EPO targeted the monocytic lineage by increasing the number of bone monocytes/macrophages, preosteoclasts, and mature osteoclasts. In contrast to the attenuated bone formation in vivo, EPO treatment in vitro did not inhibit osteoblast differentiation and activity, suggesting an indirect effect of EPO on osteoblasts. However, EPO had a direct effect on preosteoclasts by stimulating osteoclastogenesis in isolated cultures (+60%) via the Jak2 and PI3K pathways. In summary, our findings demonstrate that EPO negatively regulates bone mass and thus bears significant clinical implications for the potential management of patients with endogenously or therapeutically elevated EPO levels.

Adding heat to the live-high train-low altitude model: a practical insight from professional football

Objectives

To examine with a parallel group study design the performance and physiological responses to a 14-day off-season ‘live high-train low in the heat’ training camp in elite football players.

Methods

Seventeen professional Australian Rules Football players participated in outdoor football-specific skills (32±1°C, 11.5 h) and indoor strength (23±1°C, 9.3 h) sessions and slept (12 nights) and cycled indoors (4.3 h) in either normal air (NORM, n=8) or normobaric hypoxia (14±1 h/day, FiO₂ 15.2–14.3%, corresponding to a simulated altitude of 2500–3000 m, hypoxic (HYP), n=9). They completed the Yo-Yo Intermittent Recovery level 2 (Yo-YoIR2) in temperate conditions (23±1°C, normal air) precamp (Pre) and postcamp (Post). Plasma volume (PV) and haemoglobin mass (Hb_mass) were measured at similar times and 4 weeks postcamp (4WPost). Sweat sodium concentration ((Na⁺)_sweat) was measured Pre and Post during a heat-response test (44°C).

Results

Both groups showed very large improvements in Yo-YoIR2 at Post (+44%; 90% CL 38, 50), with no between-group differences in the changes (−1%; −9, 9). Postcamp, large changes in PV (+5.6%; −1.8, 5.6) and (Na⁺)_sweat (−29%; −37, −19) were observed in both groups, while Hb_mass only moderately increased in HYP (+2.6%; 0.5, 4.5). At 4WPost, there was a likely slightly greater increase in Hb_mass (+4.6%; 0.0, 9.3) and PV (+6%; −5, 18, unclear) in HYP than in NORM.

Conclusions

The combination of heat and hypoxic exposure during sleep/training might offer a promising ‘conditioning cocktail’ in team sports.

Altitude training and haemoglobin mass from the optimised carbon monoxide rebreathing method determined by a meta-analysis

OBJECTIVE

To characterise the time course of changes in haemoglobin mass (Hbmass) in response to altitude exposure.

METHODS

This meta-analysis uses raw data from 17 studies that used carbon monoxide rebreathing to determine Hbmass prealtitude, during altitude and postaltitude. Seven studies were classic altitude training, eight were live high train low (LHTL) and two mixed classic and LHTL. Separate linear-mixed models were fitted to the data from the 17 studies and the resultant estimates of the effects of altitude used in a random effects meta-analysis to obtain an overall estimate of the effect of altitude, with separate analyses during altitude and postaltitude. In addition, within-subject differences from the prealtitude phase for altitude participant and all the data on control participants were used to estimate the analytical SD. The 'true' between-subject response to altitude was estimated from the within-subject differences on altitude participants, between the prealtitude and during-altitude phases, together with the estimated analytical SD.

RESULTS

During-altitude Hbmass was estimated to increase by ∼1.1%/100 h for LHTL and classic altitude. Postaltitude Hbmass was estimated to be 3.3% higher than prealtitude values for up to 20 days. The within-subject SD was constant at ∼2% for up to 7 days between observations, indicative of analytical error. A 95% prediction interval for the 'true' response of an athlete exposed to 300 h of altitude was estimated to be 1.1-6%.

CONCLUSIONS

Camps as short as 2 weeks of classic and LHTL altitude will quite likely increase Hbmass and most athletes can expect benefit.