Hypoxic peripheral chemoreflex stimulation-dependent cardiorespiratory coupling is decreased in swimmer athletes

Swimmer athletes showed a decreased ventilatory response and reduced sympathetic activation during peripheral hypoxic chemoreflex stimulation. Based on these observations, we hypothesized that swimmers develop a diminished cardiorespiratory coupling due to their decreased hypoxic peripheral response. To resolve this hypothesis, we conducted a study using coherence time-varying analysis to assess the cardiorespiratory coupling in swimmer athletes. We recruited 12 trained swimmers and 12 control subjects for our research. We employed wavelet time-varying spectral coherence analysis to examine the relationship between the respiratory frequency (Rf ) and the heart rate (HR) time series during normoxia and acute chemoreflex activation induced by five consecutive inhalations of 100% N2 . Comparing swimmers to control subjects, we observed a significant reduction in the hypoxic ventilatory responses to N2 in swimmers (0.012 ± 0.001 vs. 0.015 ± 0.001 ΔVE /ΔVO2 , and 0.365 ± 0.266 vs. 1.430 ± 0.961 ΔVE /ΔVCO2 /ΔSpO2 , both p < 0.001, swimmers vs. control, respectively). Furthermore, the coherence at the LF cutoff during hypoxia was significantly lower in swimmers compared to control subjects (20.118 ± 3.502 vs. 24.935 ± 3.832 area under curve [AUC], p < 0.012, respectively). Our findings strongly indicate that due to their diminished chemoreflex control, swimmers exhibited a substantial decrease in cardiorespiratory coupling during hypoxic stimulation.

Intrahospital supervised exercise training improves survival rate among hypertensive patients with COVID-19

Among the people most affected by coronavirus disease 2019 (COVID-19) are those suffering from hypertension (HTN). However, pharmacological therapies for HTN are ineffective against COVID-19 progression and severity. It has been proposed that exercise training (EX) could be used as post-COVID treatment, which does not rule out the possible effects during hospitalization for COVID-19. Therefore, we aimed to determine the impact of supervised EX on HTN patients with COVID-19 during hospitalization. Among a total of 1,508 hospitalized patients with COVID-19 (confirmed by PCR), 439 subjects were classified as having HTN and were divided into two groups: EX (n = 201) and control (n = 238) groups. EX (3-4 times/wk during all hospitalizations) consisted of aerobic exercises (15-45 min; i.e., walking); breathing exercises (10-15 min) (i.e., diaphragmatic breathing, pursed-lip breathing, active abdominal contraction); and musculoskeletal exercises (8-10 sets of 12-15 repetitions/wk; lifting dumbbells, standing up and sitting, lumbar stabilization). Our data revealed that the EX (clinician: patient, 1:1 ratio) intervention was able to improve survival rates among controlled HTN patients with COVID-19 during their hospitalization when compared with the control group (chi-squared: 4.83; hazard ratio: 1.8; 95% CI: 1.117 to 2.899; P = 0.027). Multivariate logistic regression analysis revealed that EX was a prognostic marker (odds ratio: 0.449; 95% CI: 0.230-0.874; P = 0.018) along with sex and invasive and noninvasive mechanical ventilation. Our data showed that an intrahospital supervised EX program reduced the mortality rate among patients with HTN suffering from COVID-19 during their hospitalization.NEW & NOTEWORTHY In the present study, we found that exercise training improves the survival rate in hypertensive patients with COVID-19 during their hospitalization period. Our results provide strong evidence for the therapeutic efficacy of exercise training as a feasible approach to improving the outcomes of patients with COVID-19 who suffer from hypertension during their hospitalization.

Vertical and Leg stiffness modeling during running: effect of speed and incline

A spring mass model is often used to describe human running, allowing to understand the concept of elastic energy storage and restitution. The stiffness of the spring is a key parameter and different methods have been developed to estimate both the vertical and the leg stiffness components. Nevertheless, the validity and the range of application of these models are still debated. The aim of the present study was to compare three methods (i.e., Temporal, Kinetic and Kinematic-Kinetic) of stiffness determination. Twenty-nine healthy participants equipped with reflective markers performed 5-min running bouts at four running speeds and eight inclines on an instrumented treadmill surrounded by a tri-dimensional motion camera system. The three methods provided valid results among the different speeds, but the reference method (i.e., Kinematic-Kinetic) provided higher vertical stiffness and lower leg stiffness than the two other methods (both p<0.001). On inclined terrain, the method using temporal parameters provided non valid outcomes and should not be used. Finally, this study highlights that both the assumption of symmetry between compression and decompression phases or the estimation of the vertical displacement and changes in leg length are the major sources of errors when comparing different speeds or different slopes.

Both Hypoxia and Hypobaria Impair Baroreflex Sensitivity but through Different Mechanisms

Baroreflex sensitivity (BRS) is a measure of cardiovagal baroreflex and is lower in normobaric and hypobaric hypoxia compared to normobaric normoxia. The aim of this study was to assess the effects of hypobaria on BRS in normoxia and hypoxia. Continuous blood pressure and ventilation were recorded in eighteen seated participants in normobaric normoxia (NNx), hypobaric normoxia (HNx), normobaric hypoxia (NHx) and hypobaric hypoxia (HHx). Barometric pressure was matched between NNx vs. NHx (723±4 mmHg) and HNx vs. HHx (406±4 vs. 403±5 mmHg). Inspired oxygen pressure (PiO₂) was matched between NNx vs. HNx (141.2±0.8 vs. 141.5±1.5 mmHg) and NHx vs. HHx (75.7±0.4 vs. 74.3±1.0 mmHg). BRS was assessed using the sequence method. BRS significantly decreased in HNx, NHx and HHx compared to NNx. Heart rate, mean systolic and diastolic blood pressures did not differ between conditions. There was the specific effect of hypobaria on BRS in normoxia (BRS was lower in HNx than in NNx). The hypoxic and hypobaric effects do not add to each other resulting in comparable BRS decreases in HNx, NHx and HHx. BRS decrease under low barometric pressure requires future studies independently controlling O₂ and CO₂ to identify central and peripheral chemoreceptors' roles.

Health Benefits of Residence at Moderate Altitude Do Not Reduce COVID-19 Mortality

Moderate altitude (1000−2000 m above sea level) residence is emerging as a protective factor from the mortality of various causes, including of cardiovascular diseases. Conversely, mortality from certain respiratory diseases is higher at these altitudes than in lowlands. These divergent outcomes could indicate either beneficial or detrimental effects of altitude on the mortality of COVID-19 that primarily infects the respiratory tract but results in multi-organ damage. Previous epidemiological data indeed suggest divergent outcomes of moderate to high altitude residence in various countries. Confounding factors, such as variations in the access to clinical facilities or selection biases of investigated populations, may contribute to the equivocation of these observations. We interrogated a dataset of the complete population of an Alpine country in the center of Europe with relatively similar testing and clinical support conditions across altitude-levels of residence (up to around 2000 m) to assess altitude-dependent mortality from COVID-19 throughout 2020. While a reduced all-cause mortality was confirmed for people living higher than 1000 m, no differences in the mortality from COVID-19 between the lowest and the highest altitude regions were observed for the overall population and the population older than 60 years as well. Conversely, COVID-19 mortality seems to have been reduced in the very old (>85 years) women at moderate altitudes.

Adaptive R-Peak Detection on Wearable ECG Sensors for High-Intensity Exercise

OBJECTIVE

Continuous monitoring of biosignals via wearable sensors has quickly expanded in the medical and wellness fields. At rest, automatic detection of vital parameters is generally accurate. However, in conditions such as high-intensity exercise, sudden physiological changes occur to the signals, compromising the robustness of standard algorithms.

METHODS

Our method, called BayeSlope, is based on unsupervised learning, Bayesian filtering, and non-linear normalization to enhance and correctly detect the R peaks according to their expected positions in the ECG. Furthermore, as BayeSlope is computationally heavy and can drain the device battery quickly, we propose an online design that adapts its robustness to sudden physiological changes, and its complexity to the heterogeneous resources of modern embedded platforms. This method combines BayeSlope with a lightweight algorithm, executed in cores with different capabilities, to reduce the energy consumption while preserving the accuracy.

RESULTS

BayeSlope achieves an F1 score of 99.3% in experiments during intense cycling exercise with 20 subjects. Additionally, the online adaptive process achieves an F1 score of 99% across five different exercise intensities, with a total energy consumption of 1.55 ±0.54 mJ.

CONCLUSION

We propose a highly accurate and robust method, and a complete energy-efficient implementation in a modern ultra-low-power embedded platform to improve R peak detection in challenging conditions, such as during high-intensity exercise.

SIGNIFICANCE

The experiments show that BayeSlope outperforms state-of-the-art QRS detectors up to 8.4% in F1 score, while our online adaptive method can reach energy savings up to 38.7% on modern heterogeneous wearable platforms.

The Impact of Training on the Loss of Cardiorespiratory Fitness in Aging Masters Endurance Athletes

Elite masters endurance athletes are considered models of optimal healthy aging due to the maintenance of high cardiorespiratory fitness (CRF) until old age. Whereas a drop in VO₂max in masters athletes has been broadly investigated, the modifying impact of training still remains a matter of debate. Longitudinal observations in masters endurance athletes demonstrated VO₂max declines between -5% and -46% per decade that were closely related to changes in training volume. Here, using regression analyses, we show that 54% and 39% of the variance in observed VO₂max decline in male and female athletes, respectively is explained by changes in training volume. An almost linear VO₂max decrease was observed in studies on young and older athletes, as well as non-athletes, starting a few days after training cessation, with a decline of as much as -20% after 12 weeks. Besides a decline in stroke volume and cardiac output, training cessation was accompanied by considerable reductions in citrate synthase and succinate dehydrogenase activity (reduction in mitochondrial content and oxidative capacity). This reduction could largely be rescued within similar time periods of training (re)uptake. It is evident that training reduction or cessation leads to a considerably accelerated VO₂max drop, as compared to the gradual aging-related VO₂max decline, which can rapidly nullify many of the benefits of preceding long-term training efforts.

Can melatonin be used as a potential antioxidant and sleep aid supplement for high-altitude travelers?

Traveling to high-altitude destinations is associated with risks such as high-altitude sicknesses and impaired sleep and performance. Although antioxidant supplementation may be beneficial, conflicting study results impede clear clinical guidelines. Herein, we highlight the potential of the antioxidant compound melatonin that is surprisingly poorly investigated in high-altitude settings.

Urine and Fecal 1H-NMR Metabolomes Differ Significantly between Pre-Term and Full-Term Born Physically Fit Healthy Adult Males

Preterm birth (before 37 weeks gestation) accounts for ~10% of births worldwide and remains one of the leading causes of death in children under 5 years of age. Preterm born adults have been consistently shown to be at an increased risk for chronic disorders including cardiovascular, endocrine/metabolic, respiratory, renal, neurologic, and psychiatric disorders that result in increased death risk. Oxidative stress was shown to be an important risk factor for hypertension, metabolic syndrome and lung disease (reduced pulmonary function, long-term obstructive pulmonary disease, respiratory infections, and sleep disturbances). The aim of this study was to explore the differences between preterm and full-term male participants' levels of urine and fecal proton nuclear magnetic resonance (¹H-NMR) metabolomes, during rest and exercise in normoxia and hypoxia and to assess general differences in human gut-microbiomes through metagenomics at the level of taxonomy, diversity, functional genes, enzymatic reactions, metabolic pathways and predicted gut metabolites. Significant differences existed between the two groups based on the analysis of ¹H-NMR urine and fecal metabolomes and their respective metabolic pathways, enabling the elucidation of a complex set of microbiome related metabolic biomarkers, supporting the idea of distinct host-microbiome interactions between the two groups and enabling the efficient classification of samples; however, this could not be directed to specific taxonomic characteristics.

Kinetics of Cardiac Remodeling and Fibrosis Biomarkers During an Extreme Mountain Ultramarathon

Objectives

The effects of ultra-distance on cardiac remodeling and fibrosis are unclear. Moreover, there are no data reporting the kinetics of cardiac alterations throughout the event and during recovery. Our aim was to investigate the kinetics of biological markers including new cardiac fibrosis biomarkers suppression of tumorigenicity 2 (ST2) and galectin-3 (Gal-3) during and after an extreme mountain ultramarathon.

Methods

Fifty experienced runners participating in one of the most challenging mountain ultramarathons (330 km, D+ 25,000 m) were enrolled in our study. Blood samples were collected at four time points: before (Pre-), at 148 km (Mid-), at the finish line (Post-), and 3 days after the recovery period (Recov-).

Results

The cardiac fibrosis biomarkers (ST2 and Gal-3) increased from Pre- to Mid-. During the second half, ST2 remained higher than pre-values as opposed to Gal-3. Necrosis, ischemia, and myocyte injury biomarkers increased until Mid- then decreased but remained higher at Recov- than Pre-values. Oxidative stress appeared at Mid-. Lipid peroxides remained higher at Recov- compared to Pre-. The maximal value in most of these biomarkers was observed at Mid- and not at Post-.

Conclusions

The present study supports biphasic kinetics of cardiac fibrosis biomarkers, with a relative recovery during the second half of the event that seems specific to this extreme event. Overall, performing at such an extreme ultramarathon seems less deleterious for the heart than shorter events.

Neuromuscular fatigability during repeated sprints assessed with an innovative cycle ergometer

PURPOSE

Repeated sprint ability is an integral component of team sports. This study aimed to evaluate fatigability development and its aetiology during and immediately after a cycle repeated sprint exercise performed until a given fatigability threshold.

METHODS

On an innovative cycle ergometer, 16 healthy males completed an RSE (10-s sprint/28-s recovery) until task failure (TF): a 30% decrease in sprint mean power (Pmean). Isometric maximum voluntary contraction of the quadriceps (IMVC), central alterations [voluntary activation (VA)], and peripheral alterations [twitch (Pt)] were evaluated before (pre), immediately after each sprint (post), at TF and 3 min after. Sprints were expressed as a percentage of the total number of sprints to TF (TS_TF). Individual data were extrapolated at 20, 40, 60, and 80% TS_TF.

RESULTS

Participants completed 9.7 ± 4.2 sprints before reaching a 30% decrease in Pmean. Post-sprint IMVCs were decreased from pre to 60% TS_TF and then plateaued (pre: 345 ± 56 N, 60% 247 ± 55 N, TF: 233 ± 57 N, p < 0.001). Pt decreased from 20% and plateaued after 40% TS_TF (p < 0.001, pre-TF = - 45 ± 13%). VA was not significantly affected by repeated sprints until 60% TS_TF (pre-TF = - 6.5 ± 8.2%, p = 0.036). Unlike peripheral parameters, VA recovered within 3 min (p = 0.042).

CONCLUSION

During an RSE, Pmean and IMVC decreases were first concomitant to peripheral alterations up to 40% TS_TF and central alterations was only observed in the second part of the test, while peripheral alterations plateaued. The distinct recovery kinetics in central versus peripheral components of fatigability further confirm the necessity to reduce traditional delays in neuromuscular fatigue assessment post-exercise.

Impact of High Altitude on Cardiovascular Health: Current Perspectives

Globally, about 400 million people reside at terrestrial altitudes above 1500 m, and more than 100 million lowlanders visit mountainous areas above 2500 m annually. The interactions between the low barometric pressure and partial pressure of O2, climate, individual genetic, lifestyle and socio-economic factors, as well as adaptation and acclimatization processes at high elevations are extremely complex. It is challenging to decipher the effects of these myriad factors on the cardiovascular health in high altitude residents, and even more so in those ascending to high altitudes with or without preexisting diseases. This review aims to interpret epidemiological observations in high-altitude populations; present and discuss cardiovascular responses to acute and subacute high-altitude exposure in general and more specifically in people with preexisting cardiovascular diseases; the relations between cardiovascular pathologies and neurodegenerative diseases at altitude; the effects of high-altitude exercise; and the putative cardioprotective mechanisms of hypobaric hypoxia.

Effect of hypoxia and nitrate supplementation on different high-intensity interval-training sessions

PURPOSE

To test the hypothesis that interval-training (IHT) would be impaired by hypoxia to a larger extent than repeated-sprint training (RSH) and that dietary nitrate (NO₃^-) would mitigate the detrimental effect of hypoxia to a larger extent during IHT than RSH.

METHODS

Thirty endurance-trained male participants performed IHT (6 × 1 min at 90%∆ with 1 min active recovery) and RSH (2 sets of 6 × 10 s "all-out" efforts with 20 s active recovery) on a cycle ergometer, allocated in one of three groups: normobaric hypoxia (~ 13% F_iO₂) + NO₃^- - HNO, n = 10; normobaric hypoxia + placebo - HPL, n = 10; normoxia (20.9% F_iO₂) + placebo - CON, n = 10. Submaximal oxygen uptake ([Formula: see text]O₂), time spent above 90% of maximal [Formula: see text]O₂ (≥ 90 [Formula: see text]O₂max) and heart rate (≥ 90 HRmax) were compared between IHT and RSH sessions and groups. Additionally, mean power output (MPO), decrement score and % of power associated with [Formula: see text]O_2max (%p[Formula: see text]O₂max) in RSH sessions were analyzed.

RESULTS

[Formula: see text]O₂ at sub-maximal intensities did not differ between training protocols and groups (~ 27 ml kg^-1 min^-1).  ≥ 90 HRmax was significantly higher in IHT compared to RSH session (39 ± 8 vs. 30 ± 8%, p = 0.03) but only in HNO group. MPO (range 360-490 W) and decrement score (10-13%) were similar between groups although %p[Formula: see text]O₂max was significantly higher (p = 0.04) in CON (166 ± 16 W) compared with both HPL (147 ± 15 W) and HNO (144 ± 10 W) groups.

CONCLUSION

IHT responses were neither more impaired by hypoxia than RSH ones. Moreover, dietary NO₃^- supplementation impacted equally IHT and RSH training responses' differences between hypoxia and normoxia.

Does living at moderate altitudes in Austria affect mortality rates of various causes? An ecological study

OBJECTIVES

The effects of altitude residence on ageing, longevity and mortality are poorly understood. While adaptations to chronic exposure to altitude may exert beneficial effects on cardiovascular risk factors and some types of cancer, an elevated risk to die from chronic respiratory diseases has been reported. Moreover, high-altitude residence may be correlated with increased depression and suicide rates. The present study tested the hypothesis that living at moderate altitudes (up to 2000 m) is associated with reduced mortality from all causes.

SETTING AND PARTICIPANTS

We used a dataset comprising all deaths (n=467 834) across 10 years of a country (Austria) characterised by varying levels of altitudes up to 2000 m.

MAIN OUTCOME MEASURES

Total number of deaths, age-standardised mortality rates (ASMRs) per 100 000 population, cause-specific ASMRs.

RESULTS

ASMRs for residents living in higher (>1000 m) versus lower (<251 m) altitude regions (with agriculture employment below 3%) were 485.8 versus 597.0 (rate ratio and 95% CI 0.81 (0.72 to 0.92); p<0.001) for men and 284.6 versus 365.5 (0.78; 0.66 to 0.91); p=0.002) for women. Higher levels of agriculture employment did not influence mortality rates. Diseases of the circulatory system and cancers were main contributors to lower mortality rates at higher altitude. Residence at higher altitude did not negatively affect mortality rates from any other diseases. We highlight gender effects and-beside environmental factors-also discuss socioeconomic factors that may be responsible for conflicting results with data from other populations.

CONCLUSIONS

Living at moderate altitude (1000-2000 m) elicits beneficial effects on all-cause mortality for both sexes, primarily due to lower ASMRs from circulatory diseases and cancer. The presented analysis on cause-specific ASMRs over a 10-year period among the entire population of an alpine country will contribute to a better understanding on the effects of altitude-related mortality.

Continuous Analysis of Marathon Running Using Inertial Sensors: Hitting Two Walls?

Marathon running involves complex mechanisms that cannot be measured with objective metrics or laboratory equipment. The emergence of wearable sensors introduced new opportunities, allowing the continuous recording of relevant parameters. The present study aimed to assess the evolution of stride-by-stride spatio-temporal parameters, stiffness, and foot strike angle during a marathon and determine possible abrupt changes in running patterns. Twelve recreational runners were equipped with a Global Navigation Satellite System watch, and two inertial measurement units clamped on each foot during a marathon race. Data were split into eight 5-km sections and only level parts were analyzed. We observed gradual increases in contact time and duty factor as well as decreases in flight time, swing time, stride length, speed, maximal vertical force and stiffness during the race. Surprisingly, the average foot strike angle decreased during the race, but each participant maintained a rearfoot strike until the end. Two abrupt changes were also detected around km 25 and km 35. These two breaks are possibly due to the alteration of the stretch-shortening cycle combined with physiological limits. This study highlights new measurable phenomena that can only be analyzed through continuous monitoring of runners over a long period of time.

Hypoxic Respiratory Chemoreflex Control in Young Trained Swimmers

During an apnea, changes in PaO₂ activate peripheral chemoreceptors to increase respiratory drive. Athletes with continuous apnea, such as breath-hold divers, have shown a decrease in hypoxic ventilatory response (HVR), which could explain the long apnea times; however, this has not been studied in swimmers. We hypothesize that the long periods of voluntary apnea in swimmers is related to a decreased HVR. Therefore, we sought to determine the HVR and cardiovascular adjustments during a maximum voluntary apnea in young-trained swimmers. In fifteen trained swimmers and twenty-seven controls we studied minute ventilation (V_E), arterial saturation (SpO₂), heart rate (HR), and autonomic response [through heart rate variability (HRV) analysis], during acute chemoreflex activation (five inhalations of pure N₂) and maximum voluntary apnea test. In apnea tests, the maximum voluntary apnea time and the end-apnea HR were higher in swimmers than in controls (p < 0.05), as well as a higher low frequency component of HRV (p < 0.05), than controls. Swimmers showed lower HVR than controls (p < 0.01) without differences in cardiac hypoxic response (CHR). We conclude that swimmers had a reduced HVR response and greater maximal voluntary apnea duration, probably due to decreased HVR.

Effects of Normobaric Hypoxia on Matched-severe Exercise and Power-duration Relationship

We investigated the effects of hypoxia on matched-severe intensity exercise and on the parameters of the power-duration relationship. Fifteen trained subjects performed in both normoxia and normobaric hypoxia (F_iO₂=0.13, ~3000 m) a maximal incremental test, a 3 min all-out test (3AOT) and a transition from rest to an exercise performed to exhaustion (T_lim) at the same relative intensity (80%∆). Respiratory and pulmonary gas-exchange variables were continuously measured (K5, Cosmed, Italy). T_lim test's V̇O₂ kinetics was calculated using a two-component exponential model. V̇O₂max (44.1±5.1 vs. 58.7±6.4 ml.kg^-1.min^-1, p<0.001) was decreased in hypoxia. In T_lim, time-to-exhaustion sustained was similar (454±130 vs. 484±169 s) despite that V̇O₂ kinetics was slower (_τ1: 31.1±5.8 vs. 21.6±4.7 s, p<0.001) and the amplitude of the V̇O₂ slow component lower (12.4±5.4 vs. 20.2±5.7 ml.kg^-1.min^-1, p<0.05) in hypoxia. CP was reduced (225±35 vs. 270±49 W, p<0.001) but W' was unchanged (11.3±2.9 vs. 11.4±2.7 kJ) in hypoxia. The changes in CP/V̇O₂max were positively correlated with changes in W' (r = 0.58, p<0.05). The lower oxygen availability had an impact on aerobic related physiological parameters, but exercise tolerance is similar between hypoxia and normoxia when the relative intensity is matched despite a slower V̇O₂ kinetics in hypoxia.

On the Use of the Repeated-Sprint Training in Hypoxia in Tennis

PURPOSE

To examine physiological and technical responses to repeated-sprint training in normobaric hypoxia at ∼3,000 m (RSH, n = 11) or in normoxia (RSN, n = 11) compared to a control group (CON, n = 8) in well-trained tennis players. Participants were 28.8 ± 5.9 years old without any previous experience of training in hypoxia.

METHODS

In addition to maintaining their usual training (CON), both RSH and RSN groups completed five tennis specific repeated-shuttle sprint sessions (4 × 5 × ∼8 s maximal sprints with ∼22 s passive recovery and ∼5 min rest between sets) over 12 days. Before (Pre), the week after (Post-1) and 3 weeks after Post-1 (Post-2), physical/technical performance during Test to Exhaustion Specific to Tennis (TEST), repeated-sprint ability (RSA) (8 × ∼20 m shuttle runs-departing every 20 s) and heart rate variability (HRV) were assessed.

RESULTS

From Pre to Post-1 and Post-2, RSH improved TEST time to exhaustion (+18.2 and +17.3%; both P < 0.001), while the "onset of blood lactate accumulation" at 4 mmol L-1 occurred at later stages (+24.4 and +19.8%, both P < 0.01). At the same time points, ball accuracy at 100% V̇O2m ax increased in RSH only (+38.2%, P = 0.003 and +40.9%, P = 0.007). Markers of TEST performance did not change for both RSN and CON. Compared to Pre, RSA total time increased significantly at Post-1 and Post-2 (-1.9 and -2.5%, P < 0.05) in RSH only and this was accompanied by larger absolute Δ total hemoglobin (+82.5 and +137%, both P < 0.001). HRV did not change either supine or standing positions.

CONCLUSION

Five repeated sprint training sessions in hypoxia using tennis specific shuttle runs improve physiological and technical responses to TEST, RSA, and accompanying muscle perfusion responses in well-trained tennis players.

High-intensity Activity in European vs. National Rugby Union Games in the best 2014-2015 Team

The purpose of this study is to evaluate the influence of competition level on running patterns for five playing position in the most successful 2014-2015 European rugby union team. Seventeen French rugby union championship and seven European rugby Champions Cup games were analysed. Global positioning system (sampling: 10 Hz) were used to determine high-speed movements, high-intensity accelerations, repeated high-intensity efforts and high-intensity micro-movements characteristics for five positional groups. During European Champions Cup games, front row forwards performed a higher number of repeated high-intensity efforts compared to National championship games (5.8±1.6 vs. 3.6±2.3; +61.1%), and back row forwards travelled greater distance both at high-speed movements (3.4±1.8 vs. 2.4±0.9 m·min^-1; +41.7%) and after high-intensity accelerations (78.2±14.0 vs. 68.1 ±13.4 m; +14.8%). In backs, scrum halves carried out more high-intensity accelerations (24.7±3.1 vs. 14.8±5.0; +66.3%) whereas outside backs completed a higher number of high-speed movements (62.7±25.4 vs. 48.3±17.0; +29.8%) and repeated high-intensity efforts (13.5±4.6 vs. 9.7±4.9;  +39.2%). These results highlighted that the competition level affected the high-intensity activity differently among the five playing positions. Consequently, training programs in elite rugby should be tailored taking into account both the level of competition and the high-intensity running pattern of each playing position.

An Updated Panorama of "Living Low-Training High" Altitude/Hypoxic Methods

With minimal costs and travel constraints for athletes, the “living low-training high” (LLTH) approach is becoming an important intervention for modern sport. The popularity of the LLTH model of altitude training is also associated with the fact that it only causes a slight disturbance to athletes' usual daily routine, allowing them to maintain their regular lifestyle in their home environment. In this perspective article, we discuss the evolving boundaries of the LLTH paradigm and its practical applications for athletes. Passive modalities include intermittent hypoxic exposure at rest (IHE) and Ischemic preconditioning (IPC). Active modalities use either local [blood flow restricted (BFR) exercise] and/or systemic hypoxia [continuous low-intensity training in hypoxia (CHT), interval hypoxic training (IHT), repeated-sprint training in hypoxia (RSH), sprint interval training in hypoxia (SIH) and resistance training in hypoxia (RTH)]. A combination of hypoxic methods targeting different attributes also represents an attractive solution. In conclusion, a growing number of LLTH altitude training methods exists that include the application of systemic and local hypoxia stimuli, or a combination of both, for performance enhancement in many disciplines.

Relationship between cardiorespiratory phase coherence during hypoxia and genetic polymorphism in humans

Key points

High altitude‐induced hypoxia in humans evokes a pattern of breathing known as periodic breathing (PB), in which the regular oscillations corresponding to rhythmic expiration and inspiration are modulated by slow periodic oscillations.

The phase coherence between instantaneous heart rate and respiration is shown to increase significantly at the frequency of periodic breathing during acute and sustained normobaric and hypobaric hypoxia.

It is also shown that polymorphism in specific genes, NOTCH4 and CAT, is significantly correlated with this coherence, and thus with the incidence of PB.

Differences in phase shifts between blood flow signals and respiratory and PB oscillations clearly demonstrate contrasting origins of the mechanisms underlying normal respiration and PB.

These novel findings provide a better understanding of both the genetic and the physiological mechanisms responsible for respiratory control during hypoxia at altitude, by linking genetic factors with cardiovascular dynamics, as evaluated by phase coherence.

Abstract

Periodic breathing (PB) occurs in most humans at high altitudes and is characterised by low‐frequency periodic alternation between hyperventilation and apnoea. In hypoxia‐induced PB the dynamics and coherence between heart rate and respiration and their relationship to underlying genetic factors is still poorly understood. The aim of this study was to investigate, through novel usage of time–frequency analysis methods, the dynamics of hypoxia‐induced PB in healthy individuals genotyped for a selection of antioxidative and neurodevelopmental genes. Breathing, ECG and microvascular blood flow were simultaneously monitored for 30 min in 22 healthy males. The same measurements were repeated under normoxic and hypoxic (normobaric (NH) and hypobaric (HH)) conditions, at real and simulated altitudes of up to 3800 m. Wavelet phase coherence and phase difference around the frequency of breathing (approximately 0.3 Hz) and around the frequency of PB (approximately 0.06 Hz) were evaluated. Subjects were genotyped for common functional polymorphisms in antioxidative and neurodevelopmental genes. During hypoxia, PB resulted in increased cardiorespiratory coherence at the PB frequency. This coherence was significantly higher in subjects with NOTCH4 polymorphism, and significantly lower in those with CAT polymorphism (HH only). Study of the phase shifts clearly indicates that the physiological mechanism of PB is different from that of the normal respiratory cycle. The results illustrate the power of time‐evolving oscillatory analysis content in obtaining important insight into high altitude physiology. In particular, it provides further evidence for a genetic predisposition to PB and may partly explain the heterogeneity in the hypoxic response.

High altitude‐induced hypoxia in humans evokes a pattern of breathing known as periodic breathing (PB), in which the regular oscillations corresponding to rhythmic expiration and inspiration are modulated by slow periodic oscillations.

The phase coherence between instantaneous heart rate and respiration is shown to increase significantly at the frequency of periodic breathing during acute and sustained normobaric and hypobaric hypoxia.

It is also shown that polymorphism in specific genes, NOTCH4 and CAT, is significantly correlated with this coherence, and thus with the incidence of PB.

Differences in phase shifts between blood flow signals and respiratory and PB oscillations clearly demonstrate contrasting origins of the mechanisms underlying normal respiration and PB.

These novel findings provide a better understanding of both the genetic and the physiological mechanisms responsible for respiratory control during hypoxia at altitude, by linking genetic factors with cardiovascular dynamics, as evaluated by phase coherence.

Defining Off-road Running: A Position Statement from the Ultra Sports Science Foundation

Off-road running continues to grow in popularity, with differing event categories existing, and terminologies are often used interchangeably and without precision. Trail running, mountain running, skyrunning, fell running, orienteering, obstacle course racing and cross-country running all take place predominantly in off-road terrain. Ultramarathon running refers to any running event over marathon distance conducted in any terrain and surface. Although some overlap may exist between these running events, mainly through the common denominator of off-road terrain, distinct features need to be recognised. As scientific interest in these activities grows, it becomes important to clarify these terms and develop a universal language for discussing these events. Similarly, off-road running athletes are generally not properly defined within the scientific literature, which makes intra- and inter-study comparisons difficult. The current position statement of the Ultra Sports Science Foundation highlights the different off-road running events and recommends clear reference to distance, surface, elevation change and altitude, type of event (continuous vs. staged), type of support, name and year of the event, governing body, and guidance on terminology. We further recommend to describe off-road running athletes by basic data, physiological determinants, training and competition characteristics in the scientific literature in order to facilitate and guide further research and practice.

Comparison of Game Movement Positional Profiles Between Professional Club and Senior International Rugby Union Players

The purpose of this study was to compare the game movement demands between professional club and senior international rugby union players. Data were obtained from 188 players from 4 professional club teams (Rabo Direct Pro12) and the affiliated international team during the 2014-15 season. Players were tracked by global positioning system (GPS) sampled at 10 Hz and were categorized into 6 different positional groups (front row forwards, FRF; second row forwards, SRF; back row forwards, BRF; half backs, HB; centres, C; outside backs, OB) and separated into playing standard (club vs. international level). Data on distance, distance per minute, high speed running, maximum velocity, sprint distance and efforts as well as repeated high-intensity locomotion efforts (RHILE) were collected. Significant effects (P<0 .05) between club and international were found for RHILE in all 6 positional groupings with a higher number of RHILE in international vs. club games. Significantly (P<0.05) greater total distance and meterage were also shown in international compared to club for OB position. The RHILE differences between club and international games whatever the positions appear of practical relevance for coaches and performance staff to concentrate on training protocols to enhance this quality as well as evaluation methods.

Cerebral and Muscle Oxygenation during Repeated Shuttle Run Sprints with Hypoventilation

Ten highly-trained Jiu-Jitsu fighters performed 2 repeated-sprint sessions, each including 2 sets of 8 x ~6 s back-and-forth running sprints on a tatami. One session was carried out with normal breathing (RSN) and the other with voluntary hypoventilation at low lung volume (RSH-VHL). Prefrontal and vastus lateralis muscle oxyhemoglobin ([O₂Hb]) and deoxyhemoglobin ([HHb]) were monitored by near-infrared spectroscopy. Arterial oxygen saturation (SpO₂), heart rate (HR), gas exchange and maximal blood lactate concentration ([La]_max) were also assessed. SpO₂ was significantly lower in RSH-VHL than in RSN whereas there was no difference in HR. Muscle oxygenation was not different between conditions during the entire exercise. On the other hand, in RSH-VHL, cerebral oxygenation was significantly lower than in RSN (-6.1±5.4 vs-1.5±6.6 µm). Oxygen uptake was also higher during the recovery periods whereas [La]_max tended to be lower in RSH-VHL. The time of the sprints was not different between conditions. This study shows that repeated shuttle-run sprints with VHL has a limited impact on muscle deoxygenation but induces a greater fall in cerebral oxygenation compared with normal breathing conditions. Despite this phenomenon, performance is not impaired, probably because of a higher oxygen uptake during the recovery periods following sprints.

Effects of Repeated-Sprint Training in Hypoxia on Tennis-Specific Performance in Well-Trained Players

This study examined the physiological, physical and technical responses to repeated-sprint training in normobaric hypoxia [RSH, inspired fraction of oxygen (FiO ₂ ) 14.5%] vs. normoxia (RSN, FiO ₂ 20.9%). Within 12 days, eighteen well-trained tennis players (RSH, n=9 vs. RSN, n=9) completed five specific repeated-sprint sessions that consisted of four sets of 5 maximal shuttle-run sprints. Testing sessions included repeated-sprint ability and Test to Exhaustion Specific to Tennis (TEST). TEST’s maximal duration to exhaustion and time to attain the ‘onset of blood lactate accumulation’ at 4 mMol.L ⁻¹ (OBLA) improvements were significantly higher in RSH compared to RSN. Change in time to attain OBLA was concomitant with observations similar in time to the second ventilatory threshold. Significant interaction (P=0.003) was found for ball accuracy with greater increase in RSH (+13.8%, P=0.013) vs. RSN (–4.6%, P=0.15). A correlation (r=0.59, P<0.001) was observed between change in ball accuracy and TEST’s time to exhaustion. Greater improvement in some tennis-specific physical and technical parameters was observed after only 5 sessions of RSH vs. RSN in well-trained tennis players.

Effects of Different Training Intensity Distributions Between Elite Cross-Country Skiers and Nordic-Combined Athletes During Live High-Train Low

Purpose: To analyze the effects of different training strategies (i.e., mainly intensity distribution) during living high – training low (LHTL) between elite cross-country skiers and Nordic-combined athletes.

Methods: 12 cross-country skiers (XC) (7 men, 5 women), and 8 male Nordic combined (NC) of the French national teams were monitored during 15 days of LHTL. The distribution of training at low-intensity (LIT), below the first ventilatory threshold (VT1), was 80% and 55% in XC and NC respectively. Daily, they filled a questionnaire of fatigue, and performed a heart rate variability (HRV) test. Prior (Pre) and immediately after (Post), athletes performed a treadmill incremental running test for determination of V˙O_2max and V˙O₂ at the second ventilatory threshold (V˙O_{2V T2}), a field roller-skiing test with blood lactate ([La-]) assessment.

Results: The training volume was in XC and NC, respectively: at LIT: 45.9 ± 6.4 vs. 23.9 ± 2.8 h (p < 0.001), at moderate intensity: 1.9 ± 0.5 vs. 3.0 ± 0.4 h, (p < 0.001), at high intensity: 1.2 ± 0.9 vs. 1.4 ± 02 h (p = 0.05), in strength (and jump in NC): 7.1 ± 1.5 vs. 18.4 ± 2.7 h, (p < 0.001). Field roller-skiing performance was improved (-2.9 ± 1.6%, p < 0.001) in XC but decreased (4.1 ± 2.6%, p < 0.01) in NC. [La-] was unchanged (-4.1 ± 14.2%, p = 0.3) in XC but decreased (-27.0 ± 11.1%, p < 0.001) in NC. Changes in field roller-skiing performance and in [La-] were correlated (r = -0.77, p < 0.001). V˙O_2max increased in both XC and NC (3.7 ± 4.2%, p = 0.01 vs. 3.7 ± 2.2%, p = 0.002) but V˙O_{2V T2} increased only in XC (7.3 ± 5.8%, p = 0.002). HRV analysis showed differences between XC and NC mainly in high spectral frequency in the supine position (HF_SU). All NC skiers showed some signs of overreaching at Post.

Conclusion: During LHTL, despite a higher training volume, XC improved specific performance and aerobic capacities, while NC did not. All NC skiers showed fatigue states. These findings suggest that a large amount of LIT with a moderate volume of strength and speed training is required during LHTL in endurance athletes.

Cognitive performance and self-reported sleepiness are modulated by time-of-day during a mountain ultramarathon

Ninety-two runners completed the study during a 168 km mountain ultramarathon (MUM). Sleepiness, self-reported sleep duration, and cognitive performance were assessed the day before the race and up to eight checkpoints during the race. Sleepiness was assessed using the Karolinska Sleepiness Scale. Cognitive performance was also assessed using the Digital Symbol Substitution Task (DSST). Runner reported 23.40 ± 22.20 minutes of sleep (mean ± SD) during the race (race time: 29.38 to 46.20 hours). Sleepiness and cognitive performance decrements increased across this race, and this was modulated by time-of-day with higher sleepiness and greater performance decrements occurring during the early morning hours. Runners who slept on the course prior to testing had poorer cognitive performance, which may suggest that naps on the course were taken due to extreme exertion. This study provides evidence that cognitive performance deficits and sleepiness in MUM are sensitive to time into race and time-of-day.

Influence of Training Load and Altitude on Heart Rate Variability Fatigue Patterns in Elite Nordic Skiers

We aimed to analyse the relationship between training load/intensity and different heart rate variability (HRV) fatigue patterns in 57 elite Nordic-skiers. 1063 HRV tests were performed during 5 years. R-R intervals were recorded in resting supine (SU) and standing (ST) positions. Heart rate, low (LF), high (HF) frequency powers of HRV were determined. Training volume, training load (TL, a.u.) according to ventilatory threshold 1 (VT1) and VT2 were measured in zones I≤VT1; VT1<II≤VT2; III>VT2, IV for strength. TL was performed at 81.6±3.5% in zone I, 0.9±0.9% in zone II, 5.0±3.6% in zone III, 11.6±6.3% in zone IV. 172 HRV tests matched a fatigue state and four HRV fatigue patterns (F) were statistically characterized as F(HF-LF-)SU_ST for 121 tests, F(LF+SULF-ST) for 18 tests, F(HF-SUHF+ST) for 26 tests and F(HF+SU) for 7 tests. The occurrence of fatigue states increased substantially with the part of altitude training time (r2=0.52, p<0.001). This study evidenced that there is no causal relationship between training load/intensity and HRV fatigue patterns. Four fatigue-shifted HRV patterns were sorted. Altitude training periods appeared critical as they are likely to increase the overreaching risks.

Perceptually Regulated Exercise Test Allows Determination of V˙O2max and Ventilatory Threshold But Not Respiratory Compensation Point In Trained Runners

This study aimed to investigate the differences in maximal oxygen uptake (V̇O_2max) and submaximal thresholds between a standard graded exercise test (GXT) and a perceptually regulated graded exercise test (PRGXT) in trained runners. Eleven well-trained middle- to long-distance runners performed both tests in a randomized order. PRGXT used incremental "clamps" of rating of perceived exertion (RPE) over 10×1-min stages on an automated treadmill equipped with a sonar sensor allowing them to change their running speed instantly and in a natural way. GXT used fixed 1 km^.h^-1 increment every minute. Ventilatory threshold (VT) and respiratory compensation point (RCP) were determined using ventilatory equivalents. No differences were found in V̇O_2max (68.0 (5.3) vs. 69.5 (5.9) ml·min^-1·kg^-1, p=0.243), minute ventilation (V̇E) (159.4 (35.0) vs. 162.4 (33.7) l·min^-1, p=0.175), heart rate (HR) (188.4 (6.9) vs. 190.7 (5.2) bpm, p=0.254) and speed (21.0 (1.7) vs. 21.1 (2.3) km·h-¹, p=0.761) between GXT and PRGXT. At VT, there were no significant differences between GXT and PRGXT for any outcome variables. For 8 of 11 subjects, it was not possible to determine RCP from ventilatory equivalent in PRGXT. GXT appears more relevant for a comprehensive gas analysis in trained runners.

Adaptations in muscle oxidative capacity, fiber size, and oxygen supply capacity after repeated-sprint training in hypoxia combined with chronic hypoxic exposure

In this study, we investigate adaptations in muscle oxidative capacity, fiber size and oxygen supply capacity in team-sport athletes after six repeated-sprint sessions in normobaric hypoxia or normoxia combined with 14 days of chronic normobaric hypoxic exposure. Lowland elite field hockey players resided at simulated altitude (≥14 h/day at 2,800-3,000 m) and performed regular training plus six repeated-sprint sessions in normobaric hypoxia (3,000 m; LHTLH; n = 6) or normoxia (0 m; LHTL; n = 6) or lived at sea level with regular training only (LLTL; n = 6). Muscle biopsies were obtained from the m. vastus lateralis before (pre), immediately after (post-1), and 3 wk after the intervention (post-2). Changes over time between groups were compared, including likelihood of the effect size (ES). Succinate dehydrogenase activity in LHTLH largely increased from pre to post-1 (~35%), likely more than LHTL and LLTL (ESs = large-very large), and remained elevated in LHTLH at post-2 (~12%) vs. LHTL (ESs = moderate-large). Fiber cross-sectional area remained fairly similar in LHTLH from pre to post-1 and post-2 but was increased at post-1 and post-2 in LHTL and LLTL (ES = moderate-large). A unique observation was that LHTLH and LHTL, but not LLTL, improved their combination of fiber size and oxidative capacity. Small-to-moderate differences in oxygen supply capacity (i.e., myoglobin and capillarization) were observed between groups. In conclusion, elite team-sport athletes substantially increased their skeletal muscle oxidative capacity, while maintaining fiber size, after only 14 days of chronic hypoxic residence combined with six repeated-sprint training sessions in hypoxia. NEW & NOTEWORTHY Our novel findings show that elite team-sport athletes were able to substantially increase the skeletal muscle oxidative capacity in type I and II fibers (+37 and +32%, respectively), while maintaining fiber size after only 14 days of chronic hypoxic residence combined with six repeated-sprint sessions in hypoxia. This increase in oxidative capacity was superior to groups performing chronic hypoxic residence with repeated sprints in normoxia and residence at sea level with regular training only.

How accurate is visual determination of foot strike pattern and pronation assessment

Nowadays, choosing adequate running shoes is very difficult, due to the high number of different designs. Nevertheless, shoes have two main characteristics to fit runners' technique and morphology: drop and arch support. Retailers' advices are usually based on the visual assessment of the customer's running technique. Such method is subjective and requires an experimented examiner while objective methods require expensive material, such as 3D motion system and pressure insoles. Therefore, the aim of this study was to determine the accuracy of foot strike pattern and pronation assessment using video cameras, compared to a gold standard motion tracking system and pressure insoles. 34 subjects had to run at 8, 12 and 16 Km/h shod and 12 Km/h barefoot during 30 s trials on a treadmill. Agreement between foot strike pattern assessment methods was between 88% and 92%. For pronation, agreement on assessment methods was between 42% and 56%. The results obtained indicate a good accuracy on foot strike pattern assessment, and a high difficulty to determine pronation with enough accuracy. There is therefore a need to develop new tools for the assessment of runner's pronation.

Sex and Exercise Intensity Do Not Influence Oxygen Uptake Kinetics in Submaximal Swimming

The aim of this study was to compare the oxygen uptake (V˙O2) kinetics in front crawl between male and female swimmers at moderate and heavy intensity. We hypothesized that the time constant for the primary phase V˙O2 kinetics was faster in men than in women, for both intensities. Nineteen well trained swimmers (8 females mean ± SD; age 17.9 ± 3.5 years; mass 55.2 ± 3.6 kg; height 1.66 ± 0.05 m and 11 male 21.9 ± 2.8 years; 78.2 ± 11.1 kg; 1.81 ± 0.08 m) performed a discontinuous maximal incremental test and two 600-m square wave transitions for both moderate and heavy intensities to determine the V˙O2 kinetics parameters using mono- and bi-exponential models, respectively. All the tests involved breath-by-breath analysis of front crawl swimming using a swimming snorkel. The maximal oxygen uptake (V˙O2max) was higher in men than in women [4,492 ± 585 ml·min⁻¹ and 57.7 ± 4.4 ml·kg⁻¹·min⁻¹ vs. 2,752.4 ± 187.9 ml·min⁻¹ (p ≤ 0.001) and 50.0 ± 5.7 ml·kg⁻¹·min⁻¹(p = 0.007), respectively]. Similarly, the absolute amplitude of the primary component was higher in men for both intensities (moderate: 1,736 ± 164 vs. 1,121 ± 149 ml·min⁻¹; heavy: 2,948 ± 227 vs. 1,927 ± 243 ml·min⁻¹, p ≤ 0.001, for males and females, respectively). However, the time constant of the primary component (τ_p) was not influenced by sex (p = 0.527) or swimming intensity (p = 0.804) (moderate: 15.1 ± 5.6 vs. 14.4 ± 5.1 s; heavy: 13.5 ± 3.3 vs. 16.0 ± 4.5 s, for females and males, respectively). The slow component in the heavy domain was not significantly different between female and male swimmers (3.2 ± 2.4 vs. 3.8 ± 1.0 ml·kg⁻¹·min⁻¹, p = 0.476). Overall, only the absolute amplitude of the primary component was higher in men, while the other V˙O2 kinetics parameters were similar between female and male swimmers at both moderate and heavy intensities. The mechanisms underlying these similarities remain unclear.

Hamstring Architectural and Functional Adaptations Following Long vs. Short Muscle Length Eccentric Training

Most common preventive eccentric-based exercises, such as Nordic hamstring do not include any hip flexion. So, the elongation stress reached is lower than during the late swing phase of sprinting. The aim of this study was to assess the evolution of hamstring architectural (fascicle length and pennation angle) and functional (concentric and eccentric optimum angles and concentric and eccentric peak torques) parameters following a 3-week eccentric resistance program performed at long (LML) vs. short muscle length (SML). Both groups performed eight sessions of 3–5 × 8 slow maximal eccentric knee extensions on an isokinetic dynamometer: the SML group at 0° and the LML group at 80° of hip flexion. Architectural parameters were measured using ultrasound imaging and functional parameters using the isokinetic dynamometer. The fascicle length increased by 4.9% (p < 0.01, medium effect size) in the SML and by 9.3% (p < 0.001, large effect size) in the LML group. The pennation angle did not change (p = 0.83) in the SML and tended to decrease by 0.7° (p = 0.09, small effect size) in the LML group. The concentric optimum angle tended to decrease by 8.8° (p = 0.09, medium effect size) in the SML and by 17.3° (p < 0.01, large effect size) in the LML group. The eccentric optimum angle did not change (p = 0.19, small effect size) in the SML and tended to decrease by 10.7° (p = 0.06, medium effect size) in the LML group. The concentric peak torque did not change in the SML (p = 0.37) and the LML (p = 0.23) groups, whereas eccentric peak torque increased by 12.9% (p < 0.01, small effect size) and 17.9% (p < 0.001, small effect size) in the SML and the LML group, respectively. No group-by-time interaction was found for any parameters. A correlation was found between the training-induced change in fascicle length and the change in concentric optimum angle (r = −0.57, p < 0.01). These results suggest that performing eccentric exercises lead to several architectural and functional adaptations. However, further investigations are required to confirm the hypothesis that performing eccentric exercises at LML may lead to greater adaptations than a similar training performed at SML.

Exposure to hypobaric hypoxia results in higher oxidative stress compared to normobaric hypoxia

Sixteen healthy exercise trained participants underwent the following three, 10-h exposures in a randomized manner: (1) Hypobaric hypoxia (HH; 3450m terrestrial altitude) (2) Normobaric hypoxia (NH; 3450m simulated altitude) and (3) Normobaric normoxia (NN). Plasma oxidative stress (malondialdehyde, MDA; advanced oxidation protein products, AOPP) and antioxidant markers (superoxide dismutase, SOD; glutathione peroxidase, GPX; catalase; ferric reducing antioxidant power, FRAP) were measured before and after each exposure. MDA was significantly higher after HH compared to NN condition (+24%). SOD and GPX activities were increased (vs. before; +29% and +54%) while FRAP was decreased (vs. before; -34%) only after 10h of HH. AOPP significantly increased after 10h for NH (vs. before; +83%), and HH (vs. before; +99%) whereas it remained stable in NN. These results provide evidence that prooxidant/antioxidant balance was impaired to a greater degree following acute exposure to terrestrial (HH) vs. simulated altitude (NH) and that the chamber confinement (NN) did likely not explain these differences.

Circadian variation of salivary immunoglobin A, alpha-amylase activity and mood in response to repeated double-poling sprints in hypoxia

PURPOSE

To assess the circadian variations in salivary immunoglobin A (sIgA) and alpha-amylase activity (sAA), biomarkers of mucosal immune function, together with mood during 2 weeks of repeated sprint training in hypoxia (RSH) and normoxia (RSN).

METHODS

Over a 2-week period, 17 competitive cross-country skiers performed six training sessions, each consisting of four sets of five 10-s bouts of all-out double-poling under either normobaric hypoxia (FiO2: 13.8%, 3000 m) or normoxia. The levels of sIgA and sAA activity and mood were determined five times during each of the first (T1) and sixth (T6) days of training, as well as during days preceding (baseline) and after the training intervention (follow-up).

RESULTS

With RSH, sIgA was higher on T6 than T1 (P = 0.049), and sAA was increased on days T1, T6, and during the follow-up (P < 0.01). With RSN, sIgA remained unchanged and sAA was elevated on day T1 only (P = 0.04). Similarly, the RSH group demonstrated reduced mood on days T1, T6, and during the follow-up, while mood was lowered only on T1 with RSN (P < 0.01).

CONCLUSIONS

The circadian variation of sIgA and sAA activity, biomarkers of mucosal immune function, as well as mood were similar on the first day of training when repeated double-poling sprints were performed with or without hypoxia. Only with RSH did the levels of sIgA and sAA activity rise with time, becoming maximal after six training sessions, when mood was still lowered. Therefore, six sessions of RSH reduced mood, but did not impair mucosal immune function.