Gregoire P Millet

University of Lausanne | UNIL · Institute of Sports Science

Significance: Oxygen is indispensable for aerobic life but its utilization exposes cells and tissues to oxidative stress; thus, tight regulation of cellular, tissue and systemic oxygen concentrations is crucial. Here, we review the current understanding of how the human organism (mal-)adapts to low (hypoxia) and high (hyperoxia) oxygen levels and...

Older individuals represent a growing population, in industrialized countries, particularly those with cardiovascular diseases, which remain the leading cause of death in western societies. Aging constitutes one of the largest risks for cardiovascular diseases. On the other hand, oxygen consumption is the foundation of cardiorespiratory fitness, wh...

Sex differences in physiological responses to various stressors, including exercise, have been well documented. However, the specific impact of these differences on exposure to hypoxia, both at rest and during exercise, has remained underexplored. Many studies on the physiological responses to hypoxia have either excluded women or included only a l...

Purpose : One hundred years ago, Hill and Lupton introduced the concept of maximal oxygen uptake ( ), which is regarded as “the principal progenitor of sports physiology.” We provide a succinct overview of the evolvement of research on , from Hill and Lupton‘s initial findings to current debates on limiting factors for and the associated role of co...

Oxidative stress is augmented under hypoxic environments, which may be attenuated with antioxidant supplementation. We investigated the effects of dietary nitrate (NO3−) supplementation combined with high-intensity training performed under hypoxic conditions on antioxidant/pro-oxidant balance. Thirty trained participants were assigned to one of thr...

Introduction : Women have generally lower body size and lean- to fat-mass ratio, lower maximal anaerobic power due to a lower muscle mass, and fewer fast-twitch fibers, although they can show higher resistance to fatigue or greater metabolic flexibility than men. These factors are well known and explain the sex differences in endurance sports such...

Objectives This study aimed to investigate the short-term effects of a 1-hour floatation-resting environmental therapy (FLO) versus conventional napping (NAP) on heart rate variability (HRV) in highly trained individuals. Methods 20 non-fatigued participants underwent a prospective randomised interventional study comparing the impacts of FLO and N...

Introduction Mountain ultramarathon induces extreme physiological stress for the human body. For instance, a decrease in total hemoglobin mass (Hbmass) due to severe hemolysis is historically suspected. Nevertheless, hematological changes following a 330-km mountain ultramarathon have to date never been investigated. Methods Blood volumes were det...

Background. Outstanding exercise performance has been associated with an exacerbated vagal outflow. Nevertheless, during high-altitude hypobaric-hypoxia (HH), there is a baroreflex-dependent parasympathetic withdrawal and exercise performance deterioration. Notably, vagal control is pivotal in exercise performance, and exogenous oxytocin (OXY) admi...

As more women engage in high-altitude activities, understanding how ovarian hormone fluctuations affect their cardiorespiratory system is essential for optimizing acclimatization to these environments. This study investigates the effects of menstrual cycle (MC) phases on physiological responses at rest, during and after submaximal exercise, at high...

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 men...

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 -...

Purpose To investigate the effects of a repeated-sprint training in hypoxia induced by voluntary hypoventilation at low lung volume (RSH-VHL) including end-expiratory breath holding (EEBH) of maximal duration. Methods Over a 4-week period, twenty elite judo athletes (10 women and 10 men) were randomly split into two groups to perform 8 sessions of...

Purpose: The long-term development of talent in endurance sports is a topic of interest. Among various factors, the importance of total hemoglobin mass (tHb mass) 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 conten...

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...

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...

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 adaptati...

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 lat...

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 [FiO 2 ] 14.5%–14.2%) for 14 days,...

Patients with sickle cell disease (SCD) exhibit high levels of reactive oxygen species and low plasma levels of lipophilic antioxidants, which may contribute to end‐organ damage and disease sequelae. Apolipoprotein A1, the major apolipoprotein of high‐density lipoprotein (HDL), is mainly secreted by the intestine and liver in the form of monomeric...

Pre-term birth elicits long-lasting physiological effects in various organ systems, potentially modulating exercise- and environmental-stress responses. To establish whether adult survivors of pre-term birth respond uniquely to sub-acute high-altitude exposure at rest and during exercise, 17 prematurely-born healthy adults (gestational age < 32 wee...

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...

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 ma...

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...

“Living High-Training Low and High” (LHTLH) is a training method used to improve physical performance at sea level. The main concept is based on the combination of physiological adaptations related to chronic “Living High-Training Low” altitude residence with additional “Repeated-Sprint training in Hypoxia” (RSH). While the effects of hypoxia on ps...

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]) ma...

We need more research that will fulfill the needs of athletes and coaches. This is a common statement, highly relevant nowadays only a few weeks before the commencement of the Olympic Games Paris 2024. To fill this gap, we have identified 6 topics that we feel coaches and athletes would be interested in learning more in order to optimize their prep...

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 sk...

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, due to their smaller airways and lung size, women, independently of their fitness level, may...

The International Olympic Committee (IOC) recently published a framework on fairness, inclusion, and nondiscrimination on the basis of gender identity and sex variations. Although we appreciate the IOC's recognition of the role of sports science and medicine in policy development, we disagree with the assertion that the IOC framework is consistent...

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...

Research in sport science has historically been performed in controlled laboratory conditions, as the analytical tools available were not portable or not adapted to field conditions. With the recent development in technologies and tools, a new field of research performed in more ecologically valid situations is emerging. This allows new insights to...

Parkinson’s disease (PD) is associated with various deficits in sensing and responding to reductions in oxygen availability (hypoxia). Here we summarize the evidence pointing to a central role of hypoxia in PD, discuss the relation of hypoxia and oxygen dependence with pathological hallmarks of PD, including mitochondrial dysfunction, dopaminergic...

Introduction Modifications in asymmetry in response to self-paced efforts have not been thoroughly documented, particularly regarding horizontally-derived ground reaction force variables. We determined the magnitude and range of gait asymmetries during 800 m track running. Methods Eighteen physical education students completed an 800 m self-paced...

Purpose : We examined the effects of increasing hypoxia severity on oxygenation kinetics in the vastus lateralis muscle during repeated treadmill sprints, using statistical parametric mapping (SPM). Methods : Ten physically active males completed 8 sprints of 5 seconds each (recovery = 25 s) on a motorized sprint treadmill in normoxia (sea level; i...

Background Heart rate variability (HRV) is a common means of monitoring responses to training, yet in professional cycling, one may question its usefulness, particularly during multi-day competitions such as Grand Tours. Objectives This study aims to report and analyze HRV responses in a male professional cyclist over a season, including the Tour...

Premature birth may result in specific cardiovascular responses to hypoxia and hypercapnia, that might hamper high-altitude acclimatization. This study investigated the consequences of premature birth on baroreflex sensitivity (BRS) under hypoxic, hypobaric and hypercapnic conditions. Seventeen pre-term born males (gestational age, 29 ± 1 weeks), a...

Purpose : This study aimed to investigate acute psychophysiological responses to repeated-sprint training in hypoxia (RSH) combined with whole-body cryotherapy (WBC). Method : Sixteen trained cyclists performed 3 sessions in randomized order: RSH, WBC-RSH (WBC pre-RSH), and RSH-WBC (WBC post-RSH). RSH consisted of 3 sets of 5 × 10-second sprints wi...

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...

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 b...

The (patho-)physiological responses to hypoxia are highly heterogeneous between individuals. In this review, we focused on the roles of sex differences, which emerge as important factors in the regulation of the body’s reaction to hypoxia. Several aspects should be considered for future research on hypoxia-related sex differences, particularly alti...

Background 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 revi...

The muscle molecular adaptations to different exercise intensities in combination with hypoxia are not well understood. This study investigated the effect of low- and supramaximal-intensity hypoxic training on muscle metabolic gene expression in mice. C57BL/6 mice were divided into two groups: sedentary and training. Training consisted of 4 weeks a...

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...

Pre‐term birth is associated with physiological sequelae that persist into adulthood. In particular, modulated ventilatory responsiveness to hypoxia and hypercapnia has been observed in this population. Whether pre‐term birth per se causes these effects remains unclear. Therefore, we aimed to assess pulmonary ventilation and blood gases under vario...

Purpose Hot water immersion (HWI) has gained popularity to promote muscle recovery, despite limited data on the optimal heat dose. The purpose of this study was to compare the responses of two exogenous heat strains on core body temperature, hemodynamic adjustments, and key functional markers of muscle recovery following exercise‐induced muscle dam...

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 c...

Purpose: Total hemoglobin mass (tHbmass) and blood volume (BV) are important determinants of maximal oxygen uptake and endurance capacity. Higher-caliber endurance athletes usually possess higher tHbmass and BV values. This study aimed to compare tHbmass and BV among swimmers of diverse competitive calibers and distances. Methods: Thirty swimmer...

Purpose Laboratory tests are commonly performed by cross‐country (XC) skiers due to the challenges of obtaining reliable performance indicators on snow. However, only a few studies have reported reliability data for ski‐specific test protocols. Therefore, this study examined the test–retest reliability of ski‐specific aerobic, sprint, and neuromusc...

The objective of this study was to determine whether the relationships between energy cost of running (Cr) and running mechanics during downhill (DR), level (LR) and uphill (UR) running could be related to fitness level. Nineteen athletes performed four experimental tests on an instrumented treadmill: one maximal incremental test in LR, and three r...

Background: Elite sport is continuously evolving. World records keep falling and athletes from a longer list of countries are involved. Purpose: This commentary was designed to provide insights into present and future trends associated with world-class endurance training based on the perspectives, experience, and knowledge of an expert panel of...

Feedback of power during running is a promising tool for training and determining pacing strategies. However, current power estimation methods show low validity and are not customized for running on different slopes. To address this issue, we developed three machine-learning models to estimate peak horizontal power for level, uphill, and downhill r...