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The year 2018 marked the 50th anniversary of the Mexico Olympic games, which represents the starting point of scientific research on hypoxic training. Since the original Live High Train High, many altitude/hypoxic training methods have been developed. The aim of the present review is to present the most recent method called Repeated Sprint training in Hypoxia (RSH). RSH is of unprecedented interest in the altitude training area with 25 studies published in the 5-year period following the pioneer article in 2013, and with only two studies that did not report any beneficial effects.Potential mechanisms include transcriptional factors involved in oxygen-signaling and oxygen-carrying capacity and mitochondrial metabolism enzymes, improved behavior of fasttwitch fibers notably via compensatory vasodilatation, improved vascular relaxation and greater microvascular oxygen delivery as well as faster rate of phosphocreatine resynthesis.In general, RSH leads to superior repeated-sprint ability (i.e., faster mean sprint times or higher power outputs associated witha better resistance to fatigue during a repeated-sprint test) in normoxic conditions. RSH where hypoxia is induced by voluntary hypoventilation at low lung volume (named VHL) may also improve repeated-sprint performance more than in normoxia. Practically, RSH benefits have been demonstrated for a large range of team- (rugby, football, LaCrosse, Australian Football, field hockey), endurance (cycling, track and field, cross-country ski), racket (tennis) or combat (Jiu-Jitsu) sports.KEY WORDS: Altitude, High-Intensity, Team-Sports, Performance, Hypoxia

The purpose of this review was to provide a synopsis of the literature concerning the physiological differences between cycling and running. By comparing physiological variables such as maximal oxygen consumption (V O(2max)), anaerobic threshold (AT), heart rate, economy or delta efficiency measured in cycling and running in triathletes, runners or cyclists, this review aims to identify the effects of exercise modality on the underlying mechanisms (ventilatory responses, blood flow, muscle oxidative capacity, peripheral innervation and neuromuscular fatigue) of adaptation. The majority of studies indicate that runners achieve a higher V O(2max) on treadmill whereas cyclists can achieve a V O(2max) value in cycle ergometry similar to that in treadmill running. Hence, V O(2max) is specific to the exercise modality. In addition, the muscles adapt specifically to a given exercise task over a period of time, resulting in an improvement in submaximal physiological variables such as the ventilatory threshold, in some cases without a change in V O(2max). However, this effect is probably larger in cycling than in running. At the same time, skill influencing motor unit recruitment patterns is an important influence on the anaerobic threshold in cycling. Furthermore, it is likely that there is more physiological training transfer from running to cycling than vice versa. In triathletes, there is generally no difference in V O(2max) measured in cycle ergometry and treadmill running. The data concerning the anaerobic threshold in cycling and running in triathletes are conflicting. This is likely to be due to a combination of actual training load and prior training history in each discipline. The mechanisms surrounding the differences in the AT together with V O(2max) in cycling and running are not largely understood but are probably due to the relative adaptation of cardiac output influencing V O(2max) and also the recruitment of muscle mass in combination with the oxidative capacity of this mass influencing the AT. Several other physiological differences between cycling and running are addressed: heart rate is different between the two activities both for maximal and submaximal intensities. The delta efficiency is higher in running. Ventilation is more impaired in cycling than in running. It has also been shown that pedalling cadence affects the metabolic responses during cycling but also during a subsequent running bout. However, the optimal cadence is still debated. Central fatigue and decrease in maximal strength are more important after prolonged exercise in running than in cycling. [ABSTRACT FROM AUTHOR]

A widely cited recommendation is that to elicit valid maximal oxygen uptake (V-dotO(2max)) values, incremental exercise tests should last between 8 and 12 minutes. However, this recommendation originated from the findings of a single experimental study conducted by Buchfuhrer et al. in 1983. Although this study is an important contribution to scientific knowledge, it should not be viewed as sufficient evidence to support the recommendation for eliciting valid V-dotO(2max) values.At least eight studies have reported that durations as short as 5 minutes and as long as 26 minutes elicit V-dotO(2max) values similar to those derived from tests of 8-12 minutes' duration. Two studies reported that the shorter test protocols elicited significantly higher V-dotO(2max) values in untrained men and women. In three studies that reported significantly higher V-dotO(2max) values determined during tests of 8-12 minutes than during more prolonged tests, the prolonged tests were associated with maximal treadmill grades of 20-25%, compared with 6-10% in the shorter tests. Therefore, intolerable treadmill grades, rather than the prolonged test duration, may have limited the ability to elicit V-dotO(2max).In view of the available evidence, test administrators, reviewers and journal editors should not view 8-12 minutes' duration for incremental exercise tests as obligatory for valid V-dotO(2max) determination. Current evidence suggests that to elicit valid V-dotO(2max) values, cycle ergometer tests should last between 7 and 26 minutes and treadmill tests between 5 and 26 minutes. This is dependent on the qualification that short tests are preceded by an adequate warm-up and that treadmill grades do not exceed 15%. Current research is too limited to indicate appropriate test duration ranges for discontinuous test protocols, or protocols incorporating high treadmill grades. [ABSTRACT FROM AUTHOR]

The aim of this study was to carry out a statistical analysis of the Banister model to verify how useful it is in monitoring the training programmes of elite swimmers. The accuracy, the ill-conditioning and the stability of this model were thus investigated. The training loads of nine elite swimmers, measured over one season, were related to performances with the Banister model. First, to assess accuracy, the 95% bootstrap confidence interval (95% CI) of parameter estimates and modelled performances were calculated. Second, to study ill-conditioning, the correlation matrix of parameter estimates was computed. Finally, to analyse stability, iterative computation was performed with the same data but minus one performance, chosen at random. Performances were related to training loads for all participants (R(2) = 0.79 +/- 0.13, P < 0.05) and the estimation procedure seemed to be stable. Nevertheless, the range of 95% CI values of the most useful parameters for monitoring training was wide: t(a) = 38 (17, 59), t(f) = 19 (6, 32), t(n) = 19 (7, 35), t(g) = 43 (25, 61). Furthermore, some parameters were highly correlated, making their interpretation worthless. We suggest possible ways to deal with these problems and review alternative methods to model the training-performance relationships. [ABSTRACT FROM AUTHOR]

PURPOSE: The aim of this study was to test the hypothesis that intermittent hypoxic interval training improves sea level cycling performance more than equivalent training in hypoxia or normoxia. METHODS: Thirty-three well-trained cyclists and triathletes (25.9 +/- 2.7 yr, VO(2max) 66.1 +/- 6.1 mL.min(-1).kg(-1)) were divided into three groups: intermittent hypoxic (IHT, N = 11, P(I)O(2) of 100 mm Hg), intermittent hypoxic interval training (IHIT, N = 11) and normoxia (Nor, N = 11, P(I)O(2) of 160 mm Hg) and completed a 7-wk training program, consisting of two high-intensity (100 or 90% relative peak power output) interval training sessions each week. Each interval training session was performed in a laboratory on the subject's own bicycle, in normoxic or hypoxic conditions for the Nor and the IHT group, respectively. The IHIT group performed warm-up and cool-down plus recovery from each interval in hypoxic conditions. In contrast to IHT, interval exercise bouts were performed in normoxic conditions. RESULTS: Mean power output during a 10-min cycle time trial improved after the first 4 wk of training by 5.2 +/- 3.9, 3.7 +/- 5.9, and 5.0 +/- 3.4% for IHIT, IHT, and Nor, respectively, without significant differences between groups. Moreover, mean power output did not show any significant improvement in the following 3 wk in any group. VO(2max) (L.min(-1)) increased only in IHIT during the training period (8.7 +/- 9.1%; P < 0.05). No changes in cycling efficiency or in hematological variables (P > 0.05) were observed. CONCLUSION: Four weeks of interval training induced an improvement in endurance performance. However, short-term exposure to hypoxia (approximately 114 min.wk(-1)) did not elicit a greater increase in performance or any hematological modifications. [ABSTRACT FROM AUTHOR]

The purposes of this study were (1) to determine the time sustained above 90% of VO2max in different intermittent running sessions having the same overall time run at the velocity (vVO2max) associated with VO2max, and (2) to test whether the use of a fixed-fraction (50%) of the time to exhaustion at vVO2max (Tlim) leads to longer time spent at a high percentage of VO2max. Subjects were 8 triathletes who, after determination of their track vVO2max and Tlim, performed three intermittent running sessions alternating the velocity between 100% and 50% of vVO2max, termed 30 s-30 s, 60 s-30 s, and 1/2 Tlim, where the overall time at vVO2max was similar (= 3 x Tlim). VO2max achieved in the incremental test was 71.1 +/- 3.9 ml.min-1.kg-1 and Tlim was 236 +/- 49 s. VO2peak and peak heart rate were lower in 30 s-30 s than in the other intermittent runs. The time spent above 90% of VO2max was significantly (p < 0.001) longer either in 60 s-30 s (531 +/- 187 s) or in 1/2 Tlim-1/2 Tlim (487 +/- 176 s) than in 30 s-30 s (149 +/- 33 s). Tlim was negatively correlated with the time (in % of Tlim) spent above 90% of VO2max in 30 s-30 s (r = -0.75, p < 0.05). Tlim was also correlated with the difference of time spent over 90% of VO2max between 60 s-30 s and 30 s-30 s (r = 0.77, p < 0.05), or between 1/2 Tlim-1/2 Tlim and 30 s-30 s (r = 0.97, p < 0.001). The results confirm that vVO2max and Tlim are useful for setting interval-training sessions. However, the use of an individualized fixed-fraction of Tlim did not lead to longer time spent at a high percentage of VO2max compared to when using a fixed work-interval duration. [ABSTRACT FROM AUTHOR]

Premature birth impairs cardiac and ventilatory responses to both hypoxia and hypercapnia, but little is known about cerebrovascular responses. Both at sea level and after 2 days at high altitude (3375 m), 16 young preterm-born (gestational age, 29 ± 1 weeks) and 15 age-matched term-born (40 ± 0 weeks) adults were exposed to two consecutive 4 min bouts of hyperoxic hypercapnic conditions (3% CO 2 -97% O 2 ; 6% CO 2 -94% O 2 ), followed by two periods of voluntary hyperventilation-induced hypocapnia. We measured middle cerebral artery blood velocity, end-tidal CO 2 , pulmonary ventilation, beat-by-beat mean arterial pressure and arterialized capillary blood gases. Baseline middle cerebral artery blood velocity increased at high altitude compared with sea level in term-born (+24 ± 39%, P = 0.036), but not in preterm-born (-4 ± 27%, P = 0.278) adults. The end-tidal CO 2 , pulmonary ventilation and mean arterial pressure were similar between groups at sea level and high altitude. Hypocapnic cerebrovascular reactivity was higher at high altitude compared with sea level in term-born adults (+173 ± 326%, P = 0.026) but not in preterm-born adults (-21 ± 107%, P = 0.572). Hypercapnic reactivity was altered at altitude only in preterm-born adults (+125 ± 144%, P < 0.001). Collectively, at high altitude, term-born participants showed higher hypocapnic (P = 0.012) and lower hypercapnic (P = 0.020) CO 2 reactivity compared with their preterm-born peers. In conclusion, exposure to high altitude revealed different cerebrovascular responses in preterm- compared with term-born adults, despite similar ventilatory responses. These findings suggest a blunted cerebrovascular response at high altitude in preterm-born adults, which might predispose these individuals to an increased risk of high-altitude illnesses. KEY POINTS: Cerebral haemodynamics and cerebrovascular reactivity in normoxia are known to be similar between term-born and prematurely born adults. In contrast, acute exposure to high altitude unveiled different cerebrovascular responses to hypoxia, hypercapnia and hypocapnia. In particular, cerebral vasodilatation was impaired in prematurely born adults, leading to an exaggerated cerebral vasoconstriction. Cardiovascular and ventilatory responses to both hypo- and hypercapnia at sea level and at high altitude were similar between control subjects and prematurely born adults. Other mechanisms might therefore underlie the observed blunted cerebral vasodilatory responses in preterm-born adults at high altitude., (© 2023 The Authors. The Journal of Physiology © 2023 The Physiological Society.)

The present study investigated the maintenance/repeatability of expiratory flow limitation (EFL) between normoxia and hypoxia. Fifty-one healthy active individuals (27 men and 24 women) performed a lung function test and a maximal incremental cycling test in both normoxia and hypoxia (inspired oxygen fraction = 0.14) on two separate visits. During exercise in normoxia, 28 participants exhibited EFL (55 %). In hypoxia, another cohort of 28 participants exhibited EFL. The two groups only partly overlapped. Individuals with EFL only in normoxia reported lower maximal ventilation values in hypoxia than in normoxia (n=5; -13.5 ± 7.8 %) compared to their counterparts with EFL only in hypoxia (n=5; +6.7 ± 6.3 %) or without EFL (n=18; +5.1 ± 10.3 %) (p=0.004 and p<0.001, respectively). EFL development may be induced by different mechanisms in hypoxia vs. normoxia since the individuals who exhibited flow limitation were not the same between the two environmental conditions. This change seems influenced by the magnitude of the maximal ventilation change., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Intermittent hypoxia (IH) is commonly associated with pathological conditions, particularly obstructive sleep apnoea. However, IH is also increasingly used to enhance health and performance and is emerging as a potent non-pharmacological intervention against numerous diseases. Whether IH is detrimental or beneficial for health is largely determined by the intensity, duration, number and frequency of the hypoxic exposures and by the specific responses they engender. Adaptive responses to hypoxia protect from future hypoxic or ischaemic insults, improve cellular resilience and functions, and boost mental and physical performance. The cellular and systemic mechanisms producing these benefits are highly complex, and the failure of different components can shift long-term adaptation to maladaptation and the development of pathologies. Rather than discussing in detail the well-characterized individual responses and adaptations to IH, we here aim to summarize and integrate hypoxia-activated mechanisms into a holistic picture of the body's adaptive responses to hypoxia and specifically IH, and demonstrate how these mechanisms might be mobilized for their health benefits while minimizing the risks of hypoxia exposure., (© 2023 The Authors. The Journal of Physiology © 2023 The Physiological Society.)

The relationship between the variations in ovarian hormones (i.e., estrogens and progesterone) and the hypoxic ventilatory response (HVR) remains unclear. HVR is a key adaptive mechanism to high altitude and has been proposed as a predictor for acute mountain sickness (AMS). This study aimed to explore the effects of hormonal changes across the menstrual cycle on HVR. Additionally, it assessed the predictive capacity of HVR for AMS and examined whether a particular menstrual phase could enhance its predictive accuracy. Thirteen eumenorrheic women performed a pure nitrogen breathing test near sea level, measuring HVR and cerebral oxygenation in early follicular, late follicular, and mid-luteal phases. Oxidative stress and ovarian hormone levels were also measured. AMS symptoms were evaluated after spending 14 h, including one overnight, at an altitude of 3,375 m. No differences in HVR, ventilation, peripheral oxygen saturation, or cerebral oxygenation were observed between the three menstrual cycle phases. Moreover, these parameters and the oxidative stress markers did not differ between the women with or without AMS (31% vs 69%), regardless of the menstrual cycle phase. In conclusion, ventilatory responses and cerebral oxygenation in normobaric hypoxia were consistent across the menstrual cycle. Furthermore, these parameters did not differentiate women with or without AMS., (© 2024. The Author(s).)

Over the past decade, numerous studies have investigated an innovative "live low-train high" approach based on the repetition of short (<30 s) "all-out" sprints with incomplete recoveries in hypoxia; the so-called Repeated-Sprint training in Hypoxia (RSH). The aims of the present review are therefore threefold. First, this study summarizes the available evidence on putative additional performance enhancement after RSH comparing to the same training in normoxia (RSN). Second, a critical analysis of underpinning mechanisms discusses how advantages can be obtained through RSH for sea-level performance enhancement. An enhanced microcirculatory vasodilation leading to improved muscle perfusion and/or oxygenation and an increase in muscular phosphocreatine content may help explain the superiority of RSH vs. RSN. Third, the present review aims to provide guidelines for coaches, athletes and scientists to apply RSH interventions with regard to the interval duration, exercise-to-rest ratio and training volume. In conclusion, this review supports repeated-sprint training in hypoxia as an efficient (but not magic) training intervention with 77% of the controlled studies reporting an additional benefit with added hypoxia, mainly for team-, combat- and racket-sports athletes but also for all other sports (e.g. endurance) that require repeated accelerations with lesser fatigue.

Background: Determining thresholds by measuring blood lactate levels (lactate thresholds) or gas exchange (ventilatory thresholds) that delineate the different exercise intensity domains is crucial for training prescription. This systematic review with meta-analyses aims to assess the overall validity of the first and second heart rate variability - derived threshold (HRVT1 and HRVT2, respectively) by computing global effect sizes for agreement and correlation between HRVTs and reference - lactate and ventilatory (LT-VTs) - thresholds. Furthermore, this review aims to assess the impact of subjects' characteristics, HRV methods, and study protocols on the agreement and correlation between LT-VTs and HRVTs., Methods: Systematic computerised searches for studies determining HRVTs during incremental exercise in humans were conducted. The agreements and correlations meta-analyses were conducted using a random-effect model. Causes of heterogeneity were explored by subgroup analysis and meta-regression with subjects' characteristics, incremental exercise protocols, and HRV methods variables. The methodological quality was assessed using QUADAS-2 and STARD HRV tools. The risk of bias was assessed by funnel plots, fail-safe N test, Egger's test of the intercept, and the Begg and Mazumdar rank correlation test., Results: Fifty included studies (1160 subjects) assessed 314 agreements (95 for HRVT1, 219 for HRVT2) and 246 correlations (82 for HRVT1, 164 for HRVT2) between LT-VTs and HRVTs. The standardized mean differences were trivial between HRVT1 and LT1-VT1 (SMD = 0.08, 95% CI -0.04-0.19, n = 22) and between HRVT2 and LT2-VT2 (SMD = -0.06, 95% CI -0.15-0.03, n = 42). The correlations were very strong between HRVT1 and LT1-VT1 (r = 0.85, 95% CI 0.75-0.91, n = 22), and between HRVT2 and LT2-VT2 (r = 0.85, 95% CI 0.80-0.89, n = 41). Moreover, subjects' characteristics, type of ergometer, or initial and incremental workload had no impact on HRVTs determination., Conclusion: HRVTs showed trivial differences and very strong correlations with LT-VTs and might thus serve as surrogates. These results emphasize the usefulness of HRVTs as promising, accessible, and cost-effective means for exercise and clinical prescription purposes., (© 2024. The Author(s).)

We examined the effect of prolonged tennis playing on lower limb muscles' activity during the execution of first and second tennis serves. Ten male competitive tennis players executed five first and second serves before (pretest) and after (posttest) a 3-h tennis match. Surface electromyographic (EMG) activity of four lower limb muscles (vastus lateralis, rectus femoris, gastrocnemius lateralis, and soleus muscles) on each leg was recorded along with maximum ball velocity measured by a radar gun and peak vertical forces recorded by a force platform. For the vastus lateralis, gastrocnemius lateralis, and soleus muscles of the left leg as well as the vastus lateralis muscle of the right leg, EMG amplitude decreased from pre- to posttests (p ≤ 0.033). These reductions in the EMG signal were generally more pronounced in the first serve (i.e., ranging from -10% to -40%) compared to the second serve (0% to -25%). Maximum ball velocity for both first (159 ± 12 vs. 154 ± 12 km/h) and second (126 ± 20 vs. 125 ± 15 km/h) serves remained unchanged from pre- to posttests (p = 0.638) Similarly, peak vertical forces did not differ between pretest and posttest for both first (1.78 ± 0.30 vs. 1.72 ± 0.29 body weight) and second (1.62 ± 0.25 vs. 1.75 ± 0.23 body weight) serves (p = 0.730). In conclusion, a 3-h tennis match led to decreased activation levels in various leg muscles during serves, particularly in first serves compared to second serves. Despite consistent maximum ball velocity and peak vertical forces, these reductions in EMG signals suggest that skilled tennis players may adopt compensatory strategies after prolonged play., (© 2024 The Author(s). European Journal of Sport Science published by Wiley‐VCH GmbH on behalf of European College of Sport Science.)

Citherlet, Tom, Antoine Raberin, Giorgio Manferdelli, Nicolas Bourdillon, and Grégoire P Millet. Impact of the menstrual cycle (MC) on the cardiovascular and ventilatory responses during exercise in normoxia and hypoxia. High Alt Med Biol. 00:00-00, 2024. Introduction: Ovarian hormones influence several physiological functions in women. This study investigated how the hormonal variations across the menstrual cycle (MC) impact cardiovascular and ventilatory responses during rest and moderate exercise in normobaric hypoxia. Methods: Thirteen eumenorrheic women were tested during the early follicular (Fol1), late follicular (Fol2), and mid-luteal (Lut3) phases with measurement of hormonal levels. Heart rate (HR) variability, blood pressure, and baroreflex sensitivity (BRS) were evaluated at rest in normoxia. Ventilation (VE), peripheral oxygen saturation, and HR were monitored at rest and during moderate-intensity cycling exercise in hypoxia (F i O 2 = 14%). Results: Despite expected hormone level variations, no significant changes were observed across the MC in HR variability (root mean square of successive differences; 64 (95% confidence interval [47, 81]) at Fol1, 54 [42, 66] at Fol2, 60 [44, 77] ms at Lut3), blood pressure (mean blood pressure; 85 [79, 90]), 87 [81, 93]), 84 [77, 92] mmHg), BRS (26 [17, 36], 28 [20, 35], 23 [17, 29] ms/mmHg), VE (rest: 8.9 [7.9, 9.8], 9.5 [9.0, 9.9], 9.0 [8.1, 9.9]; exercise: 53 [41, 66], 51.1 [36.4, 65.7], 54.4 [34.0, 74.8] l/min), peripheral oxygen saturation (rest: 89.8 [87.4, 92.1], 91.9 [88.7, 95.0], 90.2 [87.8, 92.6]; exercise: 80.5 [77.4, 83.5], 84.4 [80.4, 88.3], 81.9 [78.3, 85.4] %) HR (rest: 69.7 [60.2, 79.1], 70.8 [63.2, 78.3], 70.5 [64.0, 77.0]; exercise: 148 [136, 160], 146 [132, 161], 146 [132, 160] bpm), and cycling efficiency (0.17 [0.16, 0.18], 0.17 [0.13, 0.21], 0.16 [0.15, 0.18] %) (all p > 0.05). Discussion: From a practical point of view, there is no strong evidence of any usefulness of monitoring hormonal variations and the MC phases for women exercising in hypoxia.

Purpose: The long-term development of talent in endurance sports is a topic of interest. Among various factors, the importance of total hemoglobin mass (tHbmass) and the potential benefits of being an altitude-native athlete remain unclear, particularly in young categories. This study aimed to investigate the impact of altitude and training content on hematological characteristics by comparing young male cyclists age 15-16 and 17-18 years who were born and trained at a moderate altitude (ie, greater than or equal to 2500 m; MA) and cyclists who were born and trained at low altitude (below 1000 m; LA)., Methods: tHbmass (in grams and grams per kilogram), measured by using the optimized carbon monoxide rebreathing method during an incremental test on a cycle ergometer; hematocrit percentage, hemoglobin concentration; and erythrocyte, blood, and plasma volume were measured in youth male cyclists age 15-16 years and junior cyclists age 17-18 years who were born and trained at MA versus LA. All variables were analyzed with a 2-way (age [youth cyclist vs junior cyclist] × altitude level [MA vs LA]) analysis of variance with subsequent Tuckey post hoc test., Results and Conclusion: Some altitude-induced benefits were reported in cyclists at age 15-16 years in the MA group with higher values in hematocrit percentage, hemoglobin concentration, and tHbmass (grams per kilogram) (P < .05) than their LA counterparts. This was also observed at age 17-18 years (P < .001), except for tHbmass, wherein no significant difference was found between MA and LA groups. In contrast, plasma volume was lower in MA than LA junior cyclists., New Findings: (1) The altitude of birth and residence could generate an advantage in tHbmass in young male cyclists age 15-16 and 17-18 years who train at MA compared with cyclists who are born and train at LA. (2) Altitude-induced benefits in physiological variables (hematocrit percentage, hemoglobin concentration, tHbmass in g·kg-1) were reported in cyclists at age 15-16 years and partially at age 17-18 years. In contrast, plasma volume was lower in MA than in LA junior cyclists. This may impact the strategies for identifying and developing talent in cycling.

Purpose: Elite swimmers often schedule altitude training camps ahead of major events in an attempt to maximize performance. However, the relationships between altitude-induced hematological changes, markers of training adaptation, and performance changes in such context are unclear. This study assessed hematological status, markers of daily adaptation, and swimming performance in elite middle-distance and distance swimmers during a 22-day altitude training camp at 2,320 m, 2 weeks prior to World Championship qualification competition., Methods: Venous blood was obtained and total hemoglobin mass (tHb mass ) measured (CO rebreathing) in 7 elite swimmers (4 females, 3 males) 8 days before and on day 22 of the altitude camp. Resting heart rate, peripheral oxygen saturation, urinary specific gravity, body mass, fatigue and self-reported sleep duration and quality were monitored daily during the altitude camp. Swimming performance was assessed through a standardized set (6 sets of 4 maximal repetitions of 100 m front crawl) on days 3, 10 and 17 of the camp, and at sea level competitions (200 m-1,500 m) immediately after the camp, and 2 weeks later., Results: tHb mass (+5.6 ± 3.3%; range: 2.1%-11.0%; p < 0.05), red blood cell count, hemoglobin concentration, hematocrit increased at the end of the training camp ( p < 0.05). Performance at altitude improved throughout the camp (+1.4 ± 0.4%; range: 0.7%-2.5%; p < 0.05). No significant relationship was noted between hematological changes, the change in altitude performance and any of the monitored daily markers of adaptation during the camp. Compared to the swimmers' previous personal best, competition performances did not improve immediately (2.5% ± 1.9% slower times) and 2 weeks after altitude (1.2% ± 1.4% slower times)., Conclusion: The 22-day altitude training camp at 2,320 m was beneficial for elite swimmers' tHb mass , hematological status and performance at altitude, but these benefits did not clearly translate into enhanced sea level performance immediately after or 2 weeks later. The present study confirms the large inter-individual variability in hematological responses to altitude training, and that the improvement in performance at altitude and sea level may depend on factors other than the increase in tHb mass alone., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Mujika, Bourdillon, Zelenkova, Vergnoux and Millet.)

Preterm birth elicits long-lasting physiological effects in various organ systems, potentially modulating exercise and environmental stress responses. To establish whether prematurely-born adults respond uniquely during early high-altitude acclimatization at rest and during exercise, 17 healthy adults born preterm (gestational age < 32 wk) and 17 term-born, age- and aerobic-capacity-matched, control participants completed a three-day high-altitude sojourn (3,375 m). Oxygen uptake, pulmonary ventilation, and hemodynamic responses, as well as pulse oxygen saturation, brain tissue saturation index (TSI), and skeletal muscle TSI, were measured daily at rest and during moderate-intensity steady-state exercise bouts. In general, the prematurely-born group displayed comparable acclimatization responses at rest, with similar ventilation and cardiac output observed between groups throughout. Resting brain TSI was, however, higher in the preterm group upon arrival at high altitude (72 ± 7% vs. 68 ± 3%; d = 1.20). Absolute exercising oxygen uptake was lower in the preterm participants ( P = 0.047), with this group displaying lower exercising cardiac output underpinned by reduced stroke volume (both P = 0.035). Nevertheless, exercising minute ventilation (V̇e) did not differ between groups ( P = 0.237) while brain TSI (70 ± 6% vs. 66 ± 3%; d = 1.35) and pulse oxygen saturation (85 ± 3% vs. 82 ± 5%; d = 1.52) were higher with prematurity upon arrival to high altitude. These findings suggest that healthy prematurely-born adults exhibit comparable early acclimatization patterns to their term-born counterparts and better maintain cerebral oxygenation at rest. Together, these data suggest that prematurely-born adults should not be discouraged from high-altitude sojourns involving physical activity. NEW & NOTEWORTHY The acclimatization pattern across three days at 3,375 m, at rest and during moderate-intensity exercise, was similar between healthy adults born prematurely and their term-born counterparts. Preterm adults free from respiratory complications were found to better maintain brain tissue and capillary oxygen saturation at high altitudes, whereas the term-born group experienced larger altitude-induced reductions. Despite apparent cardiac limitations, preterm individuals tolerated exercise similarly to their term-born peers. These findings underscore the notion that preterm birth per se does not predispose healthy adults to decreased altitude tolerance during exercise.

Purpose: Both maximal-intensity exercise and altitude exposure challenge the pulmonary system that may reach its maximal capacities. Expiratory flow limitation (EFL) and exercise-induced hypoxemia (EIH) are common in endurance-trained athletes. Furthermore, because of their smaller airways and lung size, women, independently of their fitness level, may be more prone to pulmonary limitations during maximal-intensity exercise, particularly when performed in hypoxic conditions. The objective of this study was to investigate the impact of sex and fitness level on pulmonary limitations during maximal exercise in normoxia and their consequences in acute hypoxia., Methods: Fifty-one participants were distributed across four different groups according to sex and fitness level. Participants visited the laboratory on three occasions to perform maximal incremental cycling tests in normoxia and hypoxia (inspired oxygen fraction = 0.14) and two hypoxic chemosensitivity tests. Pulmonary function and ventilatory capacities were evaluated at each visit., Results: EIH was more prevalent (62.5% vs 22.2%, P = 0.004) and EFL less common (37.5% vs 70.4%, P = 0.019) in women than men. EIH prevalence was different ( P = 0.004) between groups of trained men (41.7%), control men (6.7%), trained women (50.0%), and control women (75.0%). All EIH men but only 40% of EIH women exhibited EFL. EFL individuals had higher slope ratio ( P = 0.029), higher ventilation (V̇ E ) ( P < 0.001), larger ΔVO 2max ( P = 0.019), and lower hypoxia-related V̇ E increase ( P < 0.001)., Conclusions: Women reported a higher EIH prevalence than men, regardless of their fitness level, despite a lower EFL prevalence. EFL seems mainly due to the imbalance between ventilatory demands and capacities. It restricts ventilation, leading to a larger performance impairment during maximal exercise in hypoxic conditions., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

Purpose: We examined changes in stride temporal parameters and spring-mass model characteristics during repeated sprints following a 3-week period of "live high-train low and high" (LHTLH) altitude training in team-sport players., Methods: While residing under normobaric hypoxia (≥14 h/d; inspired oxygen fraction [FiO2] 14.5%-14.2%) for 14 days, elite field hockey players performed, in addition to their regular field hockey practice in normoxia, 6 sessions (4 × 5 × 5-s maximal sprints; 25-s passive recovery; 5-min rest) under either normobaric hypoxia (LHTLH; FiO2 ∼14.5%, n = 11) or normoxia (live high-train low; FiO2 20.9%, n = 12). A control group (live low-train low; FiO2 ∼20.9%, n = 9) residing in normoxia without additional repeated-sprint training was included. Before (Pre) and a few days (Post-1) and 3 weeks (Post-2) after the intervention, stride mechanics were assessed during an overground repeated-sprint test (8 × 20 m, 20-s recovery). Two-way repeated-measures analysis of variance (time [Pre, Post-1, and Post-2] × condition [LHTLH, live high-train low, and live low-train low]) were conducted., Results: Peak sprinting speed increased in LHTLH from Pre to Post-1 (+2.2% [2.0%]; P = .002) and Post-2 (+2.0% [2.4%]; P = .025), with no significant changes in live high-train low and live low-train low. There was no main effect of time (all P ≥ .062), condition (all P ≥ .771), or a significant time × condition interaction (all P ≥ .230) for any stride temporal variable (contact time, flight time, stride frequency, and stride length) or spring-mass model characteristics (vertical and leg stiffness)., Conclusions: Peak sprinting speed improved in elite field hockey players following LHTLH altitude training, while stride mechanical adjustments to repeated overground sprints remained unchanged for at least 3 weeks postintervention.

Background: The aim of this study is to explore the effect of treadmill slope on ground reaction forces and local muscle oxygenation as putative limiting factors of peak oxygen uptake in graded maximal incremental running tests. Thirteen trained male runners completed five maximal incremental running tests on treadmill at - 15%, - 7.5%, 0%, 7.5% and 15% slopes while cardiorespiratory and local muscle oxygenation responses as well as ground reaction forces were continuously recorded. Blood lactate concentration and isometric knee extensor torque were measured before and after each test., Results: Peak oxygen uptake was lower at - 15% slope compared to all other conditions (from - 10 to - 17% lower, p < 0.001), with no difference between - 7.5 and + 15% slope. Maximal heart rate and ventilation values were reached in all conditions. The negative external mechanical work increased from steep uphill to steep downhill slopes (from 6 to 92% of total external work) but was not correlated with the peak oxygen uptake reduction. Local muscle oxygenation remained higher in - 15% slope compared to level running (p = 0.003)., Conclusions: Similar peak oxygen uptake can be reached in downhill running up to - 7.5% slope. At more severe downhill slopes (i.e., - 15%), greater negative muscle work and limited local muscle deoxygenation occurred, even in subjects familiarized to downhill running, presumably preventing the achievement of similar to other condition's peak oxygen uptake., Key Points: Trained male runners can reach like level running V̇O 2peak at moderate but not at severe negative slope. Negative external mechanical work increases with increasing negative slope. At maximal intensity Vastus Lateralis muscle oxygenation is higher in steep negative slope. Knee extensor isometric muscle torque is preserved after maximal level and uphill running, but reduced after downhill running, despite lower blood lactate. Progressive reduction of V̇O 2 at maximal effort with increasing negative slope might be related to the metabolic consequences of increased lower limb negative external work (i.e., eccentric muscle actions)., (© 2024. The Author(s).)

Purpose: In recent years, there has been significant advancement in the guidelines for recovery protocols involving heat or cold water immersion. Yet, comparison between the effects of hot and cold water immersion on key markers of neuromuscular recovery following exercise-induced muscle damage (EIMD) is lacking., Methods: Thirty physically active males completed an individualized and tailored EIMD protocol immediately followed by one of the following recovery interventions: cold water immersion (11 °C, CWI11), hot water immersion (41 °C, HWI41) or warm-bath control (36 °C, CON36). Gastrointestinal temperature was tracked throughout HWI41. Knee extensors' maximal isokinetic strength [peak torque (Tpeak)] and explosive strength [late-phase rate of force development, (RFD100-200)] were measured prior to EIMD (pre-), 24 h (post-24 h) and 48 h (post-48 h) post-EIMD. In addition, pressure pain threshold (PPT) was measured to quantify the recovery from muscle soreness. Surface electromyography signals (sEMG) from the vastus lateralis were captured to extract the rates of electromyography rise (REMGR) and the spectral power in the low-frequency band., Results: At post-48 h, Tpeak returned to baseline values following both CWI11 (-8.3 ± 6.8 %, p = 0.079) and HWI41 (-1.4 ± 4.1%, p = 1). In contrast, RFD100-200 (-2.3 ± 29.3%, p = 1) and PPT (+5.6 ± 14.6%, p = 1) returned to baseline values at post-48 h only following HWI41. Spectral analysis of the sEMG signal revealed that the low-frequency band was significantly increased following CWI11 (+9.0 ± 0.52%, p = 0.012). REMGR was unchanged regardless of the condition (all p > 0.05)., Conclusions: A single session of HWI41, rather than CWI11, improved the recovery of the late-phase rate of force development following EIMD in physically active males. This suggests that in athletic contexts where a rapid force development is a key performance determinant, hot bath should be preferred over cold bath., Competing Interests: Conflict of Interest and Funding Source: The authors report no conflicts of interest. No funding was received for this research is disclosed., (Copyright © 2024 by the American College of Sports Medicine.)

Although peripheral artery disease (PAD) primarily affects large arteries outside the brain, PAD is also associated with elevated cerebral vulnerabilities, including greater risks for brain injury (such as stroke), cognitive decline and dementia. In the present review, we aim to evaluate recent literature and extract information on potential mechanisms linking PAD and consequences on the brain. Furthermore, we suggest novel therapeutic avenues to mitigate cognitive decline and reduce risk of brain injury in patients with PAD. Various interventions, notably exercise, directly or indirectly improve systemic blood flow and oxygen supply and are effective strategies in patients with PAD or cognitive decline. Moreover, triggering protective cellular and systemic mechanisms by modulating inspired oxygen concentrations are emerging as potential novel treatment strategies. While several genetic and pharmacological approaches to modulate adaptations to hypoxia showed promising results in preclinical models of PAD, no clear benefits have yet been clinically demonstrated. We argue that genetic/pharmacological regulation of the involved adaptive systems remains challenging but that therapeutic variation of inspired oxygen levels (e.g., hypoxia conditioning) are promising future interventions to mitigate associated cognitive decline in patients with PAD., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Preterm born (PTB) infants are at risk for injuries related to oxidative stress. We investigated the association between antioxidant and neurodevelopmental gene polymorphisms and oxidative stress parameters in PTB male young adults and their term-born counterparts at rest and during exercise. Healthy young PTB (N = 22) and full-term (N = 15) males underwent graded exercise tests in normobaric normoxic (F i O 2  = 0.21) and hypoxic (F i O 2  = 0.13) conditions. CAT rs1001179 was associated with decrease in nitrites in the whole group and in PTB individuals (P = 0.017 and P = 0.043, respectively). GPX1 rs1050450 was associated with decrease in ferric reducing antioxidant power in the whole group and in full-term individuals (P = 0.017 and P = 0.021, respectively). HIF1A rs11549465 was associated with decrease in nitrotyrosine and increase in malondialdehyde (P = 0.022 and P = 0.018, respectively). NOTCH4 rs367398 was associated with increase in advanced oxidation protein products and nitrites (P = 0.002 and P = 0.004, respectively) in hypoxia. In normoxia, NOTCH4 rs367398 was associated with increase in malondialdehyde in the whole group (P = 0.043). BDNF rs6265 was associated with decreased nitrites/nitrates in the whole group and in PTB individuals (P = 0.009 and P = 0.043, respectively). Polymorphisms in investigated genes and PTB might influence oxidative stress response after exercise in normoxic or hypoxic conditions far beyond the neonatal period in young male adults., (© 2024. The Author(s).)

The hypoxic chemoreflex and the arterial baroreflex are implicated in the ventilatory response to exercise. It is well known that long-term exercise training increases parasympathetic and decreases sympathetic tone, both processes influenced by the arterial baroreflex and hypoxic chemoreflex function. Hypobaric hypoxia (i.e., high altitude [HA]) markedly reduces exercise capacity associated with autonomic reflexes. Indeed, a reduced exercise capacity has been found, paralleled by a baroreflex-related parasympathetic withdrawal and a pronounced chemoreflex potentiation. Additionally, it is well known that the baroreflex and chemoreflex interact, and during activation by hypoxia, the chemoreflex is predominant over the baroreflex. Thus, the baroreflex function impairment may likely facilitate the exercise deterioration through the reduction of parasympathetic tone following acute HA exposure, secondary to the chemoreflex activation. Therefore, the main goal of this review is to describe the main physiological mechanisms controlling baro- and chemoreflex function and their role in exercise capacity during HA exposure., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Alvarez-Araos, Jiménez, Salazar-Ardiles, Núñez-Espinosa, Paez, Rodriguez-Fernandez, Raberin, Millet, Iturriaga and Andrade.)

Microvascular impairments are typical of several cardiovascular diseases. Near-infrared spectroscopy (NIRS) combined with a vascular occlusion test provides non-invasive insights into microvascular responses by monitoring skeletal muscle oxygenation changes during reactive hyperaemia. Despite increasing interest in the effects of sex and ageing on microvascular responses, evidence remains inconsistent. Therefore, the present study aimed to investigate the effects of sex and age on microvascular responsiveness. Twenty-seven participants (seven young men and seven young women; seven older men and six older women; aged 26 ± 1, 26 ± 4, 67 ± 3 and 69 ± 4 years, respectively) completed a vascular occlusion test consisting of 5 min of arterial occlusion followed by 5 min reperfusion. Oxygenation changes in the vastus lateralis were monitored by near-infrared spectroscopy. The findings revealed that both women (referring to young and older women) and older participants (referring to both men and women) exhibited lower microvascular responsiveness. Notably, both women and older participants demonstrated reduced desaturation (-38% and -59%, respectively) and reperfusion rates (-24% and -40%, respectively) along with a narrower range of tissue oxygenation (-39% and -39%, respectively) and higher minimal tissue oxygenation levels (+34% and +21%, respectively). Women additionally displayed higher values in resting (+12%) and time-to-peak (+15%) tissue oxygenation levels. In conclusion, this study confirmed decreased microvascular responses in women and older individuals. These results emphasize the importance of considering sex and age when studying microvascular responses. Further research is needed to uncover the underlying mechanisms and clinical relevance of these findings, enabling the development of tailored strategies for preserving vascular health in diverse populations., (© 2024 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Immune outcomes are key mediators of many health benefits of exercise and are determined by exercise type, dose (frequency/duration, intensity), and individual characteristics. Similarly, reduced availability of ambient oxygen (hypoxia) modulates immune functions depending on the hypoxic dose and the individual capacity to respond to hypoxia. How combined exercise and hypoxia (e.g., high-altitude training) sculpts immune responses is not well understood, although such combinations are becoming increasingly popular. Therefore, in this paper, we summarize the impact on immune responses of exercise and of hypoxia, both independently and together, with a focus on specialized cells in the innate and adaptive immune system. We review the regulation of the immune system by tissue oxygen levels and the overlapping and distinct immune responses related to exercise and hypoxia, then we discuss how they may be modulated by nutritional strategies. Mitochondrial, antioxidant, and anti-inflammatory mechanisms underlie many of the adaptations that can lead to improved cellular metabolism, resilience, and overall immune functions by regulating the survival, differentiation, activation, and migration of immune cells. This review shows that exercise and hypoxia can impair or complement/synergize with each other while regulating immune system functions. Appropriate acclimatization, training, and nutritional strategies can be used to avoid risks and tap into the synergistic potentials of the poorly studied immune consequences of exercising in a hypoxic state., (Copyright © 2023. Production and hosting by Elsevier B.V.)

Athletes increasingly engage in repeated sprint training consisting in repeated short all-out efforts interspersed by short recoveries. When performed in hypoxia (RSH), it may lead to greater training effects than in normoxia (RSN); however, the underlying molecular mechanisms remain unclear. This study aimed at elucidating the effects of RSH on skeletal muscle metabolic adaptations as compared to RSN. Sixteen healthy young men performed nine repeated sprint training sessions in either normoxia (F I O 2  = 0.209, RSN, n = 7) or normobaric hypoxia (F I O 2  = 0.136, RSH, n = 9). Before and after the training period, exercise performance was assessed by using repeated sprint ability (RSA) and Wingate tests. Vastus lateralis muscle biopsies were performed to investigate muscle metabolic adaptations using proteomics combined with western blot analysis. Similar improvements were observed in RSA and Wingate tests in both RSN and RSH groups. At the muscle level, RSN and RSH reduced oxidative phosphorylation protein content but triggered an increase in mitochondrial biogenesis proteins. Proteomics showed an increase in several S100A family proteins in the RSH group, among which S100A13 most strongly. We confirmed a significant increase in S100A13 protein by western blot in RSH, which was associated with increased Akt phosphorylation and its downstream targets regulating protein synthesis. Altogether our data indicate that RSH may activate an S100A/Akt pathway to trigger specific adaptations as compared to RSN., (© 2024 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)