Guillaume Y Millet

• PhD
• Professor (Full) at Jean Monnet University

Purpose: Despite interest in the possibility of females outperforming males in ultraendurance sporting events, little is known about the sex differences in fatigue during prolonged locomotor exercise. This study investigated possible sex differences in central and peripheral fatigue in the knee extensors and plantar flexors resulting from a 110-km...

Purpose: Sleep deprivation (SD) is characterized by reduced cognitive capabilities and endurance exercise performance and increased perceived exertion (RPE) during exercise. The combined effects of SD and exercise-induced changes in neuromuscular function and cognition are unknown. This study aimed to determine whether central fatigue is greater w...

To test the hypothesis that hypoxia centrally affects performance independently of afferent feedback and peripheral fatigue, we conducted two experiments under complete vascular occlusion of the exercising muscle under different systemic O(2) environmental conditions. In experiment 1, 12 subjects performed repeated submaximal isometric contractions...

While the industrialized world adopts a largely sedentary lifestyle, ultra-marathon running races have become increasingly popular in the last few years in many countries. The ability to run long distances is also considered to have played a role in human evolution. This makes the issue of ultra-long distance physiology important. In the ability to...

The use of electrical stimulation (ES) can contribute to our knowledge of how our neuromuscular system can adapt to physical stress or unloading. Although it has been recently challenged, the standard technique used to explore central modifications is the twitch interpolated method which consists in superimposing single twitches or high-frequency d...

Age-related declines in maximal power (Pmax) and maximal aerobic power (VO2max) impact functional capacities. Physical activity (PA) can mitigate their decline. The present study aimed to investigate the effects of age and habitual PA level on Pmax and VO2max. Thirty-nine young men (YM, 22.1 ± 3.4 years), 34 old men (OM, 71.7 ± 4.1 years) and 23 ve...

We compared neuromuscular fatigue induced by cycling at a fixed perceived effort in normoxic condition (NOR) and three purported hypoxia modalities: systemic hypoxia (SyH, FiO2 = 0.13), blood flow restriction (BFR, 50% arterial occlusion pressure) and airflow restriction mask (ARM, calibrated to ~3500 m). Seventeen healthy young participants cycled...

Purpose Red blood cells (RBCs) senescence and blood rheology during ultra-endurance running events appear to be impacted differently depending on the race distance. The physiological mechanisms underlying these differences are poorly understood. Methods We investigated the effects of three different ultra-trail running races performed in La Reunio...

Soft tissue vibrations (STV) can generate discomfort during running. Recent research has shown that footwear affects the amplitude of STV differently across runners but no studies have linked human characteristics and footwear construction yet. The purpose of this study was to investigate the runner specific STV responses to various midsole hardnes...

Introduction Cerebral palsy (CP) presents a complex neurodevelopmental disorder with a spectrum of motor impairments stemming from early brain injury. Whereas CP is traditionally viewed as a non-progressive condition, emerging evidence suggests a progressive decline in mobility and function, particularly in adulthood. Despite the prevalence of self...

Introduction: Carbon plates have been used to increase running shoes’ longitudinal bending stiffness (LBS), but their effect during a long duration run remains unknown. Our study aimed to identify the effect of LBS on energy cost of running (Cr), biomechanics, and fatigue during a half-marathon. Methods: Thirteen well-trained male runners (half-mar...

Faricier, R, Fleitas-Paniagua, PR, Iannetta, D, Millet, GY, Keir, DA, and Murias, JM. Time spent near maximal oxygen uptake during exercise at different regions of the severe-intensity domain. J Strength Cond Res XX(X): 000-000, 2024-This study applied the critical power (CP) model and several bouts of constant-power exercise within different regio...

Purpose The aim of this study was to compare performance fatigability between young (n = 13; 18–35 yr.; 23.5 ± 3.3 yr.), old (n = 13; 60–79 yr.; 68.2 ± 4.3 yr.), and very old (n = 11; ≥ 80 yr.; 85.6 ± 1.8 yr.) females during single-limb isometric (ISO) vs. isokinetic concentric (CON) vs. cycling (BIKE) fatiguing tasks. Methods Participants randoml...

The biological determinants of performance have been well described for running races up to and including the marathon (42.2 km). Ultramarathon is more complex. Events range from 50 to 5000 km in single or multiple stages, are contested in various environments and terrains, and force athletes to contend with diverse performance-limiting issues such...

This study presents a novel method for evaluating the submaximal velocity-force (V(F)) relationship in mountain ultramarathon races using crowdsourced data from Strava.com. The dataset includes positional data from 408 participants of the 171-km UTMB® 2023 race (9,850-m D+). The race was divided into 100-m segments. The mean net propulsive force an...

Purpose With aging, the decline in preferred walking speed (PWS), influenced by the increased energy cost of walking (CoW), is a key predictor of morbidity. However, the determinants associated with PWS and CoW remain poorly understood, especially after 80 years old. The aim of the study was to characterize the amplitude and mechanisms of age-relat...

Purpose: To study whether, during typical-level running, non-rear-foot strikers (non-RFS) or rear-foot strikers (RFS) presented a similar or different extent of neuromuscular fatigue after a prolonged graded run. Methods: Sixteen experienced male trail runners (8 non-RFS and 8 RFS) performed a 2.5-hour treadmill graded running exercise. Before and...

Cerebral palsy (CP) is the most common childhood-onset disability. The evolution of gait according to severity is well known amongst children and thought to peak between 8 and 12 years of age among those walking without assistive devices. However, among adults, clinical experience as well as scientific studies report, through clinical assessments,...

Footwear has the potential to reduce soft‐tissue vibrations (STV) but responses are highly subject‐specific. Recent evidence shows that compressive garments minimizing STV have a beneficial effect on neuromuscular (NM) fatigue. The aim was to determine whether an individualized midsole hardness can minimize STV and NM fatigue during a half marathon...

Transcranial magnetic stimulation (TMS) measures the excitability and inhibition of corticomotor networks. Despite its task-specificity, few studies have used TMS during dynamic movements and the reliability of TMS paired pulses has not been assessed during cycling. This study aimed to evaluate the reliability of motor evoked potentials (MEP) and s...

Purpose The perception of effort exerts influence in determining task failure during endurance performance. Training interventions blending physical and cognitive tasks yielded promising results in enhancing performance. Motor imagery can decrease the perception of effort. Whether combining motor imagery and physical training improves endurance rem...

Purpose High-intensity long-interval training (long-HIIT; interval ≥ 1 min; intensity 85–100% of maximal oxygen uptake [V̇O2max]) is often applied for cardiorespiratory adaptations; however, long-HIIT can also challenge the anaerobic and neuromuscular systems. Therefore, this study aimed to investigate the effects of 4-week long-HIIT (11 sessions)...

Introduction Chronic fatigue is the most common and debilitating symptom in people with multiple sclerosis (PwMS). Recently, exercise has been proven to alleviate chronic fatigue and improve physical functions. Tailoring the training intervention to the potential fatigue causes could optimize the beneficial effects of training on fatigue. The objec...

Introduction Central nervous system excitability depends on the task performed, muscle group solicited, and contraction type. However, little is known on corticospinal and motoneuronal excitability measured during locomotor exercise. This study aimed at determining the reliability of motor-evoked potentials (MEP) and thoracic motor-evoked potential...

Purpose Approximately 30% of people infected with COVID-19 require hospitalization and 20% of them are admitted to an intensive care unit (ICU). Most of these patients experience symptoms of fatigue weeks post-ICU, so understanding the factors associated with fatigue in this population is crucial. Methods Fifty-nine patients [38-78 yr] hospitalize...

Background Sleep and physical performance are strongly related and mutually influence each other. Athletes, particularly in disciplines like offshore sailing and ultra-endurance sports, often suffer from sleep deprivation due to factors like irregular training times, travel, and the extended duration of events like 100-mile mountain races. Despite...

Transcranial magnetic stimulation (TMS) measures the excitability and inhibition of corticomotor networks. Despite its task-specificity, few studies have used TMS during dynamic movements and the reliability of TMS-derived measures has not been assessed during cycling. This study aimed to evaluate the reliability of motor evoked potentials (MEP) an...

Purpose: High-intensity long-interval training (long-HIIT; interval≥1 min; intensity 85%-100% of maximal oxygen uptake [V̇O2max]) is often applied for cardiorespiratory adaptations, however long-HIIT can also challenge the anaerobic and neuromuscular systems. Therefore, this study aimed to investigate the effects of 4-week long-HIIT (11 sessions) o...

Red blood cells (RBC) play critical roles in the maintenance of vascular tone and metabolite transfer in addition to their well characterized role in gas exchange. In this capacity, they play a central role in maintaining systemic activity during stressful physiological situations such as exercise. At the far end of the spectrum for endurance sport...

Background Sleep and physical performance are strongly related and mutually influence each other. Athletes, particularly in disciplines like offshore sailing and ultra-endurance sports, often suffer from sleep deprivation due to factors like irregular training times, travel, and the extended duration of events like 100-mile mountain races. Despite...

Endurance sports require the sustained maintenance of high effort until the point of task failure. Psychological factors, particularly the perception of effort, exert considerable influence in determining task failure. Training interventions that blend physical and cognitive tasks yielded promising results in enhancing endurance performance. Motor...

Ultra-endurance running (UER) poses extreme mental and physical challenges that present many barriers to completion, let alone performance. Despite these challenges, participation in UER events continues to increase. With the relative paucity of research into UER training and racing compared with traditional endurance running distance (e.g., marath...

Introduction: Fatigue is the most common and disabling symptom in multiple sclerosis (MS), being reported by 55% to 78% of patients with multiple sclerosis (PwMS). Etiology of MS-related fatigue remains poorly understood but an increased neuromuscular fatigability (i.e., greater loss of torque during exercise) could contribute to this phenomenon....

Purpose: to investigate the effects of different ramp incremental (RI) slopes on fatigability and its recovery in females and males. Methods: Ten females and 11 males performed RI tests with distinct slopes, in separated and randomized sessions, 15 (RI15), 30 (RI30), and 45 (RI45) W·min-1. Performance fatigability was assessed by femoral nerve e...

Background: Scientific evidence and public health reports keep highlighting the continuous and alarming worldwide progression of physical inactivity and sedentary behaviors in children and adolescents. The present paper summarizes findings from the 2022 French Report Card (RC) on physical activity for children and youth and compares them to the 20...

Chronic fatigue is a frequent complaint, expressed at all levels of the healthcare system. It is perceived as disabling in a high proportion of cases, and internists are frequently called upon to find "the" cause. The etiological diagnostic approach of an unexplained state of fatigue relies on the careful search for more specific clues by questioni...

The psychological and psychopathological characteristics of ultra-runners have aroused growing interest in recent years. Indeed, although rare, ultramarathons may require hospitalisation, including to Intensive Care Unit (ICU). We aim to explore the relations between exercise addiction and personality traits in ultrarunners who went to ICU after a...

Purpose The effectiveness of a neuromuscular electrical stimulation (NMES) program is proportional to the level of evoked torque, which can be achieved with either conventional or wide‐pulse stimulations. The aim of this study was to compare evoked torque, objective fatigability, and related peripheral and central alterations, as well as changes in...

Abstract Purpose This study aimed to compare performance and fatigability between young (n = 13; 18-30 yr), old (n = 13; 60-80 yr) and very old (n = 12; >80 yr) men during a single-joint isometric (ISO) and concentric (CON) task performed on an isokinetic dynamometer, and a cycling (BIKE) task. Methods Participants randomly performed incremental...

Fatigue is a major symptom in many diseases, often among the most common and severe ones and may last for an extremely long period. Chronic fatigue impacts quality of life, reduces the capacity to perform activities of daily living, and has socioeconomical consequences such as impairing return to work. Despite the high prevalence and deleterious co...

Background and Objective To determine whether the gap in endurance performance between men and women is reduced as distances increase, i.e. if there is a sex difference in endurance, one can analyse the performance of elite runners, all participants, or one can pair women and men during short-distance events and examine the difference over longer d...

Purpose The effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequen...

Purpose: Previous research has shown that maximal oxygen uptake (VO2max) significantly influences performance in trail-running races up to 120 km but not beyond. Similarly, the influence of running economy on performance in ultratrail remains unclear. The aim of our study was, therefore, to determine the physiological predictors of performance in...

Besson, T, Pastor, FS, Varesco, G, Berthet, M, Kennouche, D, Dandrieux, P-E, Rossi, J, and Millet, GY. Elite vs. experienced male and female trail runners: comparing running economy, biomechanics, strength, and power. J Strength Cond Res 37(7): 1470-1478, 2023-The increased participation in trail running (TR) races and the emergence of official int...

Purpose: Carbon plates have been used to increase running shoes' longitudinal bending stiffness (LBS), leading to reductions in the energy cost of level running (Cr). However, whether or not this is true during uphill (UH) running remains unknown. The aim of our study was to identify the effect of LBS on Cr during UH running. Methods: Twenty wel...

BACKGROUND Physical inactivity is a major risk factor for noncommunicable diseases and the fourth leading cause of premature death worldwide. Nowadays, the World Health Organization (WHO) recommends performing at least 30 minutes of physical activity (PA) five times a week. However, these recommendations are independent on a person's age, gender or...

Background Physical inactivity is a major risk factor for noncommunicable diseases and a leading cause of premature death. The World Health Organization (WHO) recommends at least 150 minutes of moderate intensity physical activity (PA) weekly, regardless of age, gender, or personal habits. However, in both sports performance and clinical settings,...

Background: Though fatigue is common in the general population, most studies investigating its predictors are either outdated or under-sampled, which can lead to conflicting results. This study aims to describe the factors associated with fatigue in the general adult population. Methods: Using a web-based survey, 3008 participants were asked to sel...

This study investigated the effects of marker placement (skin- vs shoe-mounted) on metatarsophalangeal joint (MTP) kinematics and kinetics during running. Fifteen trained men ran on a 15-m track at 10 and 13 km/h with three (low, standard and high stiffness) shoe longitudinal bending stiffnesses (LBS). Reflective markers were fixed on the shoe uppe...

While neuromuscular fatigability has been previously characterized after running and cycling, no study has investigated an ultra-endurance upper body task. In preparation for a world record attempt, three pacing strategies to perform 1980 pull-ups in 6 hrs were compared during independent sessions: fast pace, long recovery (FL), fast pace, multiple...

Purpose: Monitoring fatigue is now commonly performed in athletes as it can directly impact performance and may further increase the risk of injury or overtraining syndrome. Among the exercise-induced peripheral alterations, low-frequency fatigue (LFF) assessment is commonly restricted to in-lab studies. Measuring LFF on-field would allow athletes...

During running, the human body is subjected to impacts generating repetitive soft tissue vibrations (STV). They have been frequently discussed to be harmful for the musculoskeletal system and may alter running gait. The aims of this narrative review were to: (1) provide a comprehensive overview of the literature on STV during running, especially wh...

Introduction: Cost of locomotion (CL) has been shown to increase after endurance running and cycling bouts. The main purpose of this study was to compare, in the same participants, the effect of both modalities on CL when matched for relative intensity and duration. Methods: Seventeen recreational athletes performed two incremental tests in runnin...

Whereas fatigue is recognized to be the main complaint of patients with multiple sclerosis (PwMS), its etiology, and particularly the role of resistance to fatigability and its interplay with disability level, remains unclear. The purposes of this review were to (i) clarify the relationship between fatigue/disability and neuromuscular performance i...

In the present study, we aimed to provide a robust comparison of the fatigability of the knee extensors following isometric (ISO) and concentric (CON) tasks. Twenty young adults (25 ± 4 yr, 10 women) randomly performed the ISO and CON quadriceps intermittent fatigue test, consisting of ten (5 s on/5-s off, ISO) or one-hundred (0.5-s on/0.5-s off, C...

Objectives: The aim of the present study was to investigate the level of cardiorespiratory fitness and neuromuscular function of ICU survivors after COVID-19 and to examine whether these outcomes are related to ICU stay/mechanical ventilation duration. Design: Prospective nonrandomized study. Setting: Patients hospitalized in ICU for COVID-19...

Background: Fatigue is the most prevalent symptom among people with multiple sclerosis (PwMS). Although exercise effectively reduces fatigue, the relationship between daily physical activity and fatigue has only recently been demonstrated. Objective: The aim of this study was to evaluate the prevalence of fatigue and to understand the relationsh...

Purpose The present study aimed to directly compare the effects of 30 min muscle (VIBmuscle) vs. tendon (VIBtendon) local vibration (LV) to the quadriceps on maximal voluntary isometric contraction (MVIC) and rate of torque development (RTD) as well as on central nervous system excitability (i.e. motoneuron and cortical excitability). Methods Befo...

Purpose The effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequen...

The purpose of the study was to assess sex‐related differences in resting mechanical properties and adaptations of skeletal muscles and tendons in response to trail running races of different distances using multi‐site shear wave elastography assessments of the lower limb, force capacity and blood analyses. Sex differences in resting mechanical pro...

Introduction: Performance fatigability is substantially greater when exercising in the severe versus heavy intensity domain. However, the relevance of the boundary between moderate and heavy intensity exercise, the gas exchange threshold (GET), to performance fatigability is unclear. This study compared alterations in neuromuscular function during...

The purpose of the study was to assess the influence of a preceding mountain ultramarathon on the impact between the foot and the ground and the resulting soft tissue vibrations (STV). Two sessions of measurements were performed on 52 trail runners, before and just after mountain trail running races of various distances (from 40 to 171 km). Triaxia...

The aim of this study was to investigate if acute impairments of the footwear midsole materials could interact with the modifications of the running patterns after a fatiguing trail running race. We hypothesized that introducing a control pair of shoes after the race, would modify running mechanics by partially correcting the alterations generated...

Objective: The aim of this study was to quantify fatigue and quality of life (QoL) in people self-reporting chronic venous disease (CVD) symptoms or at risk of CVD within a large cohort representative of the French population. The relationship between self-reported physical activity and both fatigue and QoL was also investigated. We hypothesized t...

Purpose: to investigate the time course and amplitude of performance fatigability during cycling at intensities around the maximal lactate steady state (MLSS) until task failure (TTF). Methods: 10 females and 11 males were evaluated in 8 visits: 1) ramp incremental test; 2-3) 30-min constant power output (PO) cycling for MLSS determination; 4-8)...

Introduction Cancer-related fatigue (CRF) is a debilitating symptom that affects around one-third of people for months or years after cancer treatment. In a recent study, we found that people with post-treatment CRF have greater performance fatigability. The aim of this secondary analysis was to examine the aetiology of performance fatigability in...

Prolonged stays in intensive care units (ICU) are responsible for long-lasting consequences, fatigue being one of the more debilitating. Yet, fatigue prevalence for patients that have experienced ICU stays remains poorly investigated. This study aimed to evaluate fatigue prevalence and the level of physical activity in ICU survivors from 6 months t...

Middle-aged and master endurance athletes exhibit similar physical performance and long-term muscle adaptation to aerobic exercise. Nevertheless, we hypothesized that the short-term plasticity of the skeletal muscle might be distinctly altered for master athletes when they are challenged by a single bout of prolonged moderate-intensity exercise. Si...

The repeated bout effect in eccentric-biased exercises is a well-known phenomenon, wherein a second bout of exercise results in attenuated strength loss and soreness compared to the first bout. We sought to determine if the repeated bout effect influences changes in lower-extremity biomechanics over the course of a 30-min downhill run. Eleven male...

Purpose: While the physiological determinants of road running have been widely studied, there is a lack of research in trail-running racing performance. The aim of our study was to determine the physiological predictors of trail-running performance in races of different distances in similar terrain and weather conditions. Methods: Seventy-five t...

Experiencing pain in one leg can alter exercise tolerance and neuromuscular fatigue (NMF) responses in the contralateral leg; however, the corticospinal modulations to nonlocal experimental pain induced by blood flow occlusion remain unknown. In three randomized visits, 13 male participants performed 25% of isometric maximal voluntary contraction (...

Sabater Pastor, FS, Besson, T, Berthet, M, Varesco, G, Kennouche, D, Dandrieux, P-E, Rossi, J, and Millet, GY. Elite road vs. trail runners: comparing economy, biomechanics, strength, and power. J Strength Cond Res 37(1): 181-186, 2023-The purpose of this study was to determine the differences between road (ROAD) vs. trail (TRAIL) elite runners in...

In recent years, there has been a significant expansion in female participation in endurance (road and trail) running. The often reported sex differences in maximal oxygen uptake (VO2max) are not the only differences between sexes during prolonged running. The aim of this narrative review was thus to discuss sex differences in running biomechanics,...

Muscle oxygen uptake (V̇O2m) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V̇O2m. However, its correspondence with pulmonary oxygen uptake (V̇O2p) during exercise remains unknown. Purpose: to investigate the V̇O2m and V...

Introduction Running and cycling represent two of the most common forms of endurance exercise. However, a direct comparison of the neuromuscular consequences of these two modalities after prolonged exercise has never been made. The aim of this study was to compare the alterations in neuromuscular function induced by matched intensity and duration...

This note is to correct errata in the paper "Internal Tibial Forces and Moments During Graded Running" published in Journal of Biomechanical Engineering, Vol. 144, p. 011009 (2021), DOI: 10.1115/1.4051924. In the Data Analysis section, it was stated that, "The joint moments used in the optimization were the flexion-extension and abduction-adduction...

Aim If the development of the oxygen uptake slow component (V̇O2SC) and muscle fatigue are related, these variables should remain coupled in a time- and intensity-dependent manner. Methods Sixteen participants (7 females) visited the laboratory on seven separate occasions: 1) three 6-min moderate-intensity cycling exercise bouts proceeded by a ram...

Background Ground reaction forces (GRFs) are important for understanding human movement, but their measurement is generally limited to a laboratory environment. Previous studies have used neural networks to predict GRF waveforms during running from wearable device data, but these predictions are limited to the stance phase of level-ground running....

Physical activity is recommended for the management of cancer-related fatigue (CRF), yet the evidence is primarily based on interventions delivered during cancer treatment, with no eligibility criterion for fatigue. There is a need to examine the quantity and quality of the existing literature on physical activity for clinically-relevant CRF that c...

Background The Rating of Fatigue (ROF) scale can measure changes in perceived fatigue in a variety of contexts. Objective The aim of the present study was to translate and subsequently validate the ROF scale in the French language. Methods The study was composed of three phases. Phase 1 involved a comprehensive translation, back-translation, and...

Background: After anterior cruciate ligament reconstruction (ACLR), quadriceps strength must be maximized as early as possible. Objectives: We tested whether local vibration training (LVT) during the early post-ACLR period (i.e., ∼10 weeks) could improve strength recovery. Methods: This was a multicentric, open, parallel-group, randomized control...

The goal of this study was to analyse the effects of ground technicity on cardio‐respiratory and biomechanical responses during uphill running. Ten experienced male trail‐runners ran ∼10.5 min at racing pace on two trails with different (high and low) a priori technicity levels. These two runs were replicated (same slope, velocity, and distance) in...

Purpose Cancer-related fatigue (CRF) is a common and distressing symptom of cancer that may persist for years following treatment completion. However, little is known about the pathophysiology of CRF. Using a comprehensive group of gold-standard physiological and psychosocial assessments, this study aimed to identify correlates of CRF in a heteroge...

Purpose: Fatigue has previously been investigated in trail running by comparing maximal isometric force before and after the race. Isometric contractions may not entirely reflect fatigue-induced changes, so that dynamic evaluation is warranted. The aim of the present study was to compare the magnitude of the decrement of maximal isometric force vs...

The stress experienced by the tibia has contributions from the forces and moments acting on the tibia. We sought to quantify the influence of running grade on internal tibial forces and moments. Seventeen participants ran at 3.33 m/s on an instrumented treadmill at 0°, ±5°, and ±10° while motion data were captured. Ankle joint contact force was est...