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    • Effect of ground technicity on cardio-respiratory and biomechanical parameters in uphill trail running

      Authors : François Nicot, Frederic Sabater-Pastor, Pierre Samozino, Guillaume Y Millet, Thomas Rupp.

      Published: 18 October 2021 - Eur J Sport Sci.


      The goal of this study was to analyze 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) indoor on a motor-driven treadmill. Oxygen uptake, minute ventilation (VE), heart rate as well as step frequency and medio-lateral feet accelerations (i.e. objective indices of uneven terrain running patterns adjustments) were continuously measured throughout all sessions. Rating of perceived exertion (RPE) and perceived technicity were assessed at the end of each bout. Oxygen cost of running (O2Cr) (+10.5%; p<0.001), VE (+21%; p<0.004) and the range and variability of feet medio-lateral accelerations (+116% and +134%, respectively; p<0.001), were significantly greater when running on trail compared to treadmill, regardless of the a priori technicity level. Despite perceived technicity being lower on treadmill (p<0.001), RPE was not different between trail and treadmill runs (p < 0.68). It is concluded that running uphill on a trail vs. a treadmill significantly elevates both O2Cr and magnitude/variability of feet medio-lateral accelerations but no difference could be identified between trails of different a priori technicities. These results strengthen the need for trainers and race organizers to consider terrain technicity per se as a challenging cardio-respiratory and biomechanical component in uphill trail running.

      Keywords:  Biomechanics; Efficiency; Endurance; Skill; feet accelerometry; gradient locomotion; key words: energy cost of running; rating of perceived exertion; uneven terrain..

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    • Physiological and psychosocial correlates of cancer-related fatigue

      Authors : Callum G Brownstein, Rosemary Twomey, John Temesi, James G Wrightson, Tristan Martin, Mary E Medysky, S Nicole Culos-Reed, Guillaume Y Millet.

      Published: 05 October 2021 - J Cancer Surviv.


      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 heterogenous group of cancer survivors.

      Methods: Using a cross-sectional design to determine the physiological and psychosocial correlates of CRF, ninety-three cancer survivors (51 fatigued, 42 non-fatigued) completed assessments of performance fatigability (i.e. the decline in muscle strength during cycling), cardiopulmonary exercise testing, venous blood samples for whole blood cell count and inflammatory markers and body composition. Participants also completed questionnaires measuring demographic, treatment-related, and psychosocial variables.

      Results: Performance fatigability, time-to-task-failure, peak oxygen uptake (V̇O2peak), tumor necrosis factor-α (TNF-α), body fat percentage, and lean mass index were associated with CRF severity. Performance fatigability, V̇O2peak, TNF-α, and age explained 35% of the variance in CRF severity. Those with clinically-relevant CRF reported more pain, more depressive symptoms, less perceived social support, and were less physically active than non-fatigued cancer survivors.

      Conclusions: The present study utilised a comprehensive group of gold-standard physiological and psychosocial assessments and the results give potential insight into the mechanisms underpinning the association between physical inactivity, physical deconditioning and CRF.

      Implications for cancer survivors: Given the associations between CRF and both physiological and psychosocial measures, this study identifies targets that can be measured by rehabilitation professionals and used to guide tailored interventions to reduce fatigue.

      Keywords: Anthropometry; Cancer-related fatigue; Exercise; Fatigability; Inflammation.

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    • Fatigue Measured in Dynamic Versus Isometric Modes After Trail Running Races of Various Distances

      Authors: Jerome Koral, Marie Fanget, Laurianne Imbert, Thibault Besson, Djahid Kennouche, Audrey Parent, Clément Foschia, Jérémy Rossi, Guillaume Y Millet

      Published: 05 August 2021 - Int J Sports Physiol Perform.


      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, and therefore dynamic evaluation is warranted. The aim of the present study was to compare the magnitude of the decrement of maximal isometric force versus maximal power, force, and velocity after trail running races ranging from 40 to 170 km.

      Methods: Nineteen trail runners completed races shorter than 60 km, and 21 runners completed races longer than 100 km. Isometric maximal voluntary contractions (IMVCs) of knee extensors and plantar flexors and maximal 7-second sprints on a cycle ergometer were performed before and after the event.

      Results: Maximal power output (Pmax; -14% [11%], P < .001), theoretical maximum force (F0; -11% [14%], P < .001), and theoretical maximum velocity (-3% [8%], P = .037) decreased significantly after both races. All dynamic parameters but theoretical maximum velocity decreased more after races longer than 100 km than races shorter than 60 km (P < .05). Although the changes in IMVCs were significantly correlated (P < .05) with the changes in F0 and Pmax, reductions in IMVCs for knee extensors (-29% [16%], P < .001) and plantar flexors (-26% [13%], P < .001) were larger (P < .001) than the reduction in Pmax and F0.

      Conclusions: After a trail running race, reductions in isometric versus dynamic forces were correlated, yet they are not interchangeable because the losses in isometric force were 2 to 3 times greater than the reductions in Pmax and F0. This study also shows that the effect of race distance on fatigue measured in isometric mode is true when measured in dynamic mode.

      Keywords: dynamic exercise; isometric maximal voluntary contraction; neuromuscular fatigue assessment; power-force-velocity profile.

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    • Effect of race distance on performance fatigability in male trail and ultra-trail runners

      Authors: John Temesi, Thibault Besson, Audrey Parent, Benjamin Singh, Vincent Martin, Callum G Brownstein, Loïc Espeit, Nicolas Royer, Diana Rimaud, Thomas Lapole, Léonard Féasson, Guillaume Y Millet.

      Published: 25 June 2021 - Scand J Med Sci Sports.


      The etiology of changes in lower-limb neuromuscular function, especially to the central nervous system, may be affected by exercise duration. Direct evidence is lacking as few studies have directly compared different race distances. This study aimed to investigate the etiology of deficits in neuromuscular function following short versus long trail-running races. Thirty-two male trail runners completed one of five trail-running races as LONG (>100 km) or SHORT (<60 km). Pre- and post-race, maximal voluntary contraction (MVC) torque and evoked responses to electrical nerve stimulation during MVCs and at rest were used to assess voluntary activation and muscle contractile properties of knee-extensor (KE) and plantar-flexor (PF) muscles. Transcranial magnetic stimulation (TMS) was used to assess evoked responses and corticospinal excitability in maximal and submaximal KE contractions. Race distance correlated with KE MVC (ρ = -0.556) and twitch (ρ = -0.521) torque decreases (P ≤ 0.003). KE twitch torque decreased more in LONG (-28 ± 14%) than SHORT (-14 ± 10%, P = 0.005); however, KE MVC time × distance interaction was not significant (P = 0.073). No differences between LONG and SHORT for PF MVC or twitch torque were observed. Maximal voluntary activation decreased similarly in LONG and SHORT in both muscle groups (P ≥ 0.637). TMS-elicited silent period decreased in LONG (P = 0.021) but not SHORT (P = 0.912). Greater muscle-contractile property impairment in longer races, not central perturbations, contributed to the correlation between KE MVC loss and race distance. Conversely, PF fatigability was unaffected by race distance.

      Keywords: fatigue; knee extensors; plantar flexors.

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    • Fatigue in trail running: interactions between sex and race distance

      Main findings of the UTMB 2019 study

      Introduction: The results of this study was analyzed only a few months after the UTMB 2019. Yet in order to communicate, we had to wait for the publication of all the results in scientific journals. This is now done. Thus, this document is a synthesis of 6 articles validated by the international scientific community: Medicine & Science in Sports & Exercise, Scandinavian Journal of Medicine & Science in SportsExperimental PhysiolologyThe International Journal of Sports Physiology and PerformanceEuropean Journal of Applied Physiology International Journal of Molecular Sciences.


    • Dépasser ses limites physiques et mentales : la performance en ultra endurance à l'épreuve de la science

      Journées d'Études de la Société Française de Psychologie du Sport

      Date: 09 June 2021

      Webconférence grand public avec l'intervention de : 

      >>  Roberta Antonini Philippe, Université de Lausanne 

      >> Guillaume Millet , Professeur de Physiologie de l’Exercice - Directeur du Laboratoire Interuniversitaire de Biologie de la Motricité - Coordinateur de la chaire ActiFS - Membre Senior de l’Institut Universitaire de France

    • Enhancing Adaptations to Neuromuscular Electrical Stimulation Training Interventions

      Authors: Anthony J Blazevich, David F Collins, Guillaume Y Millet, Marco A Vaz, Nicola A Maffiuletti

      Published: 8 June 2021 - Exerc Sport Sci Rev.


      Neuromuscular electrical stimulation (NMES) applied to skeletal muscles is an effective rehabilitation and exercise training modality. However, the relatively low muscle force and rapid muscle fatigue induced by NMES limits the stimulus provided to the neuromuscular system, and subsequent adaptations. We hypothesise that adaptations to NMES will be enhanced by the use of specific stimulation protocols and adjuvant interventions.

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    • Sex Differences in Neuromuscular Fatigue and Changes in Cost of Running after Mountain Trail Races of Various Distances

      Authors: Thibault Besson, Audrey Parent, Callum G Brownstein, Loïc Espeit, Thomas Lapole, Vincent Martin, Nicolas Royer, Diana Rimaud, Frederic Sabater Pastor, Benjamin Singh, Giorgio Varesco, Jeremy Rossi, John Temesi, Guillaume Y Millet.

      Published: 07 June 2021 - Med Sci Sports Exerc.


      Introduction: Females have been shown to experience less neuromuscular fatigue than males in knee extensors (KE) and less peripheral fatigue in plantar flexors (PF) following ultra-trail running, but it is unknown if these differences exist for shorter trail running races and whether this may impact running economy. The purpose of this study was to characterize sex differences in fatigability over a range of running distances and to examine possible differences in the post-race alteration of the cost of running (Cr).

      Methods: Eighteen pairs of males and females were matched by performance after completing different races ranging from 40 to 171 km, divided into SHORT vs LONG races (< 60 and > 100 km, respectively). NM function and Cr were tested before and after each race. NM function was evaluated on both KE and PF with voluntary and evoked contractions using electrical nerve (KE and PF) and transcranial magnetic (KE) stimulation. Oxygen uptake, respiratory exchange ratio and ventilation were measured on a treadmill and used to calculate Cr.

      Results: Compared to males, females displayed a smaller decrease in maximal strength in KE (-36% vs -27%, respectively, p < 0.01), independent of race distance. In SHORT only, females displayed less peripheral fatigue in PF compared to males (Δ peak twitch: -10% vs -24%, respectively, p < 0.05). Cr increased similarly in males and females.

      Conclusion: Females experience less neuromuscular fatigue than men following both 'classic' and 'extreme' prolonged running exercises but this does not impact the degradation of the energy cost of running.

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    • Neuromuscular, biomechanical, and energetic adjustments following repeated bouts of downhill running

      Authors: Arash Khassetarash, Gianluca Vernillo, Renata L Krüger, W Brent Edwards, Guillaume Y Millet

      Published: 04 June 2021 -  Sport Health Sci.


      Purpose: This study utilized downhill running as a model to investigate the repeated bout effect (RBE) on neuromuscular performance, running biomechanics, and metabolic cost of running.

      Methods: Ten healthy recreational male runners performed two 30-min bouts of downhill running (DR1 and DR2) at -20% slope and 2.8 m/s 3 weeks apart. Neuromuscular fatigue, level running biomechanics during slow and fast running, and running economy parameters were recorded immediately before and after the downhill bouts, and at 24 h, 48 h, 72 h, 96 h, and 168 h thereafter (i.e., follow-up days).

      Results: An RBE was confirmed by attenuated muscle soreness and serum creatine kinase rise after DR2 compared to DR1. An RBE was also observed in maximum voluntary contraction (MVC) force loss and voluntary activation (VA) where DR2 resulted in attenuated MVC force loss and VA immediately after the run and during follow-up days. The downhill running protocol significantly influenced level running biomechanics; an RBE was observed in which center of mass excursion and, therefore, lower-extremity compliance were greater during follow-up days after DR1 compared to DR2. The observed changes in level running biomechanics did not influence the energy cost of running.

      Conclusion: This study demonstrated evidence of adaptation in neural drive as well as biomechanical changes with the RBE after DR. The higher neural drive resulted in attenuated MVC force loss after the second bout. It can be concluded that the RBE after downhill running manifests as changes to global and central fatigue parameters and running biomechanics without substantially altering the energy cost of running.

      Keywords: Cost of running; Eccentric exercise; Fatigue; Muscle damage.

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    • Individualised physical activity programme in patients over 65 years with haematological malignancies (OCAPI): protocol for a single-arm feasibility trial

      Authors: Baptiste Fournier, Emmanuelle Nicolas-Virelizier, Chiara Russo, Olivia Pérol, Guillaume Y Millet, Aurélia Maire, Lidia Delrieu, Anne-Sophie Michallet, Souad Assaad, Amine Belhabri, Lila Gilis, Yann Guillermin, Laure Lebras, Philippe Rey, Clémence Santana, Emilie Pretet-Flamand, Catherine Terret, Mauricette Michallet, Béatrice Fervers.

      Published: 03 June 2021 - BMJ Open.


      Introduction: Older adults with cancer suffer from the combined effects of ageing, cancer disease and treatment side effects. The main treatment for patients with haematological malignancies is chemotherapy, associated with significant toxicities. Chemotherapy can alter patients' physical function and quality of life which are often already diminished in older patients due to ageing and comorbidities. It therefore seems essential to develop and to evaluate interventions capable of preventing physical and psychosocial decline and its consequences. Promoting physical activity is a promising approach to improve physical function and quality of life in older adults with cancer, but there are limited data on the feasibility of such interventions among older patients with haematological malignancies, concomitant to chemotherapy.

      Methods and analysis: OCAPI (OnCogeriatric and Individualized Physical Activity) is a single-arm, interdisciplinary, prospective, interventional, feasibility study. It is intended to include 40 patients (20 patients with acute myeloid leukaemia and 20 patients with non-Hodgkin's lymphoma) over 65 years in an individualised 6-month physical activity programme. The programme consists of individually supervised exercise sessions with an increasing volume of physical activity either at home and/or in a laminar airflow room (depending on the disease and treatment regimen) followed by unsupervised sessions and phone follow-ups. Patients will receive an activity tracker during the 6 months of the programme. Evaluations will take place at inclusion and at 3, 6 and 12 months to assess the feasibility of the programme and to explore potential changes in physical, psychosocial and clinical outcomes. The results will generate preliminary data to implement a larger randomised controlled trial.

      Ethics and dissemination: The study protocol was approved by the French ethics committee (Comité de protection des personnes Est I, N°ID-RCB 2019-A01231-56, 12 July 2019). All participants will have to sign and date an informed consent form. The findings will be disseminated in peer-reviewed journals and academic conferences.

      Trial registration number: NCT04052126.

      Keywords: leukaemia; lymphoma; sports medicine.

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    • Influence of wide-pulse neuromuscular electrical stimulation frequency and superimposed tendon vibration on occurrence and magnitude of extra torque

      Authors: Loïc Espeit, Vianney Rozand, Guillaume Y Millet, Julien Gondin, Nicola A Maffiuletti, Thomas Lapole.

      Published: 03 June 2021 - J Appl Physiol (1985).


      Low-frequency and high-frequency wide-pulse neuromuscular electrical stimulation (NMES) can generate extra-torque (ET) via afferent pathways. Superimposing tendon vibration (TV) to NMES can increase the activation of these afferent pathways and favour ET generation. Knowledge of the characteristics of ET is essential to implement these stimulation paradigms in clinical practice. Thus, we aimed at investigating the effects of frequency and TV superimposition on the occurrence and magnitude of ET in response to wide-pulse NMES. NMES-induced isometric plantar flexion torque was recorded in 30 healthy individuals who performed five NMES protocols: wide-pulse low-frequency (1 ms; 20 Hz; WPLF) and wide-pulse high-frequency (1 ms; 100 Hz; WPHF) without and with superimposed TV (1 mm; 100 Hz) and conventional NMES (50 µs; 20 Hz; reference protocol). Each NMES protocol began with an adjustment of NMES intensity in order to reach 10% of maximal voluntary contraction then consisted of three 20-s trains interspersed by 90 s of rest. The ET occurrence was similar for WPLF and WPHF (p=0.822). In the responders, the ET magnitude was greater for WPHF than WPLF (p<0.001). There was no effect of superimposed TV on ET characteristics. This study reported an effect of NMES frequency on ET magnitude, whereas TV superimposition did not affect this parameter. In the context of our experimental design decisions, the present findings question the clinical use of wide-pulse NMES and its combination with superimposed TV. Yet, further research is needed in order to maximize force production through the occurrence and magnitude of ET.

      Keywords : Cluster analysis; Extra-force; NMES; Responders; Triceps surae.

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    • Framework for Ultramarathon Performance with Guillaume Millet PhD

      Koopcast Episode 79

      Date: 13 May 2021

    • Bedside voluntary and evoked forces evaluation in intensive care unit patients: a narrative review

      Authors : Djahid Kennouche, Eric Luneau, Thomas Lapole, Jérôme Morel, Guillaume Y Millet, Julien Gondin.

      Published: 22 April 2021 - Crit Care.


      Around one third of intensive care unit (ICU) patients will develop severe neuromuscular alterations, known as intensive care unit-acquired weakness (ICUAW), during their stay. The diagnosis of ICUAW is difficult and often delayed as a result of sedation or delirium. Indeed, the clinical evaluation of both Medical Research Council score and maximal voluntary force (e.g., using handgrip and/or handheld dynamometers), two independent predictors of mortality, can be performed only in awake and cooperative patients. Transcutaneous electrical/magnetic stimulation applied over motor nerves combined with the development of dedicated ergometer have recently been introduced in ICU patients in order to propose an early and non-invasive measurement of evoked force. The aim of this narrative review is to summarize the different tools allowing bedside force evaluation in ICU patients and the related experimental protocols. We suggest that non-invasive electrical and/or magnetic evoked force measurements could be a relevant strategy to characterize muscle weakness in the early phase of ICU and diagnose ICUAW.

      Keywords : Electrical stimulation; Ergometers; Intensive care unit-acquired weakness; Magnetic stimulation; Skeletal muscle function.

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    • French Translation and Validation of the Rating-of-Fatigue Scale

      Authors : Callum G Brownstein, Diana Rimaud, Benjamin Singh, Laurie-Anne Fruleux-Santos, Marine Sorg, Dominic Micklewright, Guillaume Y Millet.

      Published : 08 April 2021 - Sports Med Open.


      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 consolidation process in order to produce the French ROF scale. During phase 2, the face validity of the French ROF scale was assessed. A cohort of 60 native French speaking participants responded to a range of Likert scale items which probed the purposes of the ROF scale and what it is intended to measure. During phase 3, the convergent and divergent validity of the ROF scale was assessed during ramped cycling to exhaustion and 10 min of resting recovery.

      Results: The results from phase 1 demonstrated comparability and interpretability between the original and back-translated ROF scale. In phase 2, participants reported a high face validity, with a score of 3.48 ± 0.70 out of 4 when given the item probing whether the scale "measures fatigue". This score further improved (3.67 ± 0.57, P = 0.01) after participants read the accompanying instructions. Participants were able to distinguish the purposes of the scale for measuring fatigue rather than exertion. In phase 3, strong correlations were found between ROF and heart rate (HR) both during exercise (r = 0.91, P < 0.01) and recovery (r = 0.92, P < 0.01), while discriminant validity between ROF and rating of perceived exertion (RPE) was found during recovery.

      Conclusion: The present study permits the applications of the ROF scale in the French language.

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    • Differential impacts of trail and ultra-trail running on cytokine profiles: An observational study

      Authors : Sarah Skinner, Elie Nader, Emeric Stauffer, Mélanie Robert, Camille Boisson, Agnès Cibiel, Clément Foschia, Léonard Feasson, Paul Robach, Guillaume Y Millet, Philippe Connes.

      Published : 01 April 2021 - Clin Hemorheol Microcirc.


      Background: Endurance running events are known to cause inflammation and result in increased cytokine production. However, the effects of ultramarathons on cytokine profiles are not well characterized.

      Objective: The aim of this study was to describe and compare the effects of a trail (40 km) race and an ultra-trail (171 km) race on leukocyte concentrations and cytokine profiles.

      Methods: The study was conducted during the Ultra-Trail du Mont Blanc® ultra-marathon running event, and included 11 runners who completed the 40 km trail run and 12 runners who completed the 171 km ultra-trail. Blood samples were taken before and after the races.

      Results: Leukocyte concentrations significantly increased after both races. Circulating levels of IL-6, IL-1β, MCP-1, and IFN-γ were significantly higher after the longer race compared to the shorter race. Furthermore, while both races resulted in significant increases in IL-6 and IL-8, only the longer race resulted in significant increases in MIP-1β, IL-7, IL-17a, and IL-4.

      Conclusions: These results illustrate that a 171 km ultra-trail race results in greater modulations in cytokine profiles than a traditional trail race.

      Keywords : Running; cytokines profile; exercise; inflammation; leukocytes; ultra-trail.

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    • Reductions in motoneuron excitability during sustained isometric contractions are dependent on stimulus and contraction intensity

      Authors: Callum G Brownstein, Loïc Espeit, Nicolas Royer, Paul Ansdell, Jakob Škarabot, Robin Souron, Thomas Lapole, Guillaume Y Millet.

      Published: 31 March 2021 - J Neurophysiol.


      Cervicomedullary stimulation provides a means of assessing motoneuron excitability. Previous studies demonstrated that during low-intensity sustained contractions, small cervicomedullary evoked potentials (CMEPs) conditioned using transcranial magnetic stimulation (TMS-CMEPs) are reduced, whilst large TMS-CMEPs are less affected. Since small TMS-CMEPs recruit motoneurons most active during low-intensity contractions while large TMS-CMEPs recruit a high proportion of motoneurons inactive during the task, these results suggest that reductions in motoneuron excitability could be dependent on repetitive activation. To further test this hypothesis, this study assessed changes in small and large TMS-CMEPs across low- and high-intensity contractions. Twelve participants performed a sustained isometric contraction of the elbow flexor for 4.5 min at the electromyography (EMG) level associated with 20% maximal voluntary contraction force (MVC; low-intensity) and 70% MVC (high-intensity). Small and large TMS-CMEPs with amplitudes of ~15 and ~50% Mmax at baseline, respectively, were delivered every minute throughout the tasks. Recovery measures were taken at 1, 2.5 and 4-min post-exercise. During the low-intensity trial, small TMS-CMEPs were reduced at 2-4 min (p≤0.049) by up to -10% Mmax, while large TMS-CMEPs remained unchanged (p≥0.16). During the high-intensity trial, small and large TMS-CMEPs were reduced at all time-points (p<0.01) by up to -14% and -33% Mmax, respectively, and remained below baseline during all recovery measures (p≤0.02). TMS-CMEPs were unchanged relative to baseline during recovery following the low-intensity trial (p≥0.24). These results provide novel insight into motoneuron excitability during and following sustained contractions at different intensities, and suggest that contraction-induced reductions in motoneuron excitability depend on repetitive activation.

      Keywords: cervicomedullary evoked potentials; isometric exercise; motoneuron excitability.

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    • Heat Acclimatization, Cooling Strategies, and Hydration during an Ultra-Trail in Warm and Humid Conditions

      Authors: Nicolas Bouscaren, Robin Faricier, Guillaume Y Millet, Sébastien Racinais.

      Published: 26 March 2021 - Nutrients


      The aim of this study was to assess the history of exertional heat illness (EHI), heat preparation, cooling strategies, heat related symptoms, and hydration during an ultra-endurance running event in a warm and humid environment. This survey-based study was open to all people who participated in one of the three ultra-endurance races of the Grand Raid de la Réunion. Ambient temperature and relative humidity were 18.6 ± 5.7 °C (max = 29.7 °C) and 74 ± 17%, respectively. A total of 3317 runners (56% of the total eligible population) participated in the study. Overall, 78% of the runners declared a history of heat-related symptoms while training or competing, and 1.9% reported a previous diagnosis of EHI. Only 24.3% of study participants living in temperate climates declared having trained in the heat before the races, and 45.1% of all respondents reported a cooling strategy during the races. Three quarter of all participants declared a hydration strategy. The planned hydration volume was 663 ± 240 mL/h. Fifty-nine percent of the runners had enriched their food or drink with sodium during the race. The present study shows that ultra-endurance runners have a wide variability of hydration and heat preparation strategies. Understandings of heat stress repercussions in ultra-endurance running need to be improved by specific field research.

      Keywords: acclimatization; body temperature regulation; dehydration; electrolyte balance; hot temperature; hydration; running; ultra-endurance running.

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    • The Relationship between Fatigue and Actigraphy-Derived Sleep and Rest-Activity Patterns in Cancer Survivors

      Authors: Tristan Martin, Rosie Twomey, Mary E Medysky, John Temesi, S Nicole Culos-Reed, Guillaume Y Millet.

      Published: 10 March 2021 - Curr Oncol.


      Cancer-related fatigue can continue long after curative cancer treatment. The aim of this study was to investigate sleep and rest-activity cycles in fatigued and non-fatigued cancer survivors. We hypothesized that sleep and rest-activity cycles would be more disturbed in people experiencing clinically-relevant fatigue, and that objective measures of sleep would be associated with the severity of fatigue in cancer survivors. Cancer survivors (n = 87) completed a 14-day wrist actigraphy measurement to estimate their sleep and rest-activity cycles. Fatigue was measured using the Functional Assessment of Chronic Illness Therapy Fatigue Scale (FACIT-F). Participants were dichotomised into two groups using a previously validated score (fatigued n = 51 and non-fatigued n = 36). The participant's perception of sleep was measured using the Insomnia Severity Index (ISI). FACIT-F score was correlated with wake after sleep onset (r = -0.28; p = 0.010), sleep efficiency (r = 0.26; p = 0.016), sleep onset latency (r = -0.31; p = 0.044) and Insomnia Severity Index (ISI) score (r = -0.56; p < 0.001). The relative amplitude of the rest-activity cycles was lower in the fatigued vs. the non-fatigued group (p = 0.017; d = 0.58). After treatment for cancer, the severity of cancer-related fatigue is correlated with specific objective measures of sleep, and there is evidence of rest-activity cycle disruption in people experiencing clinically-relevant fatigue.

      Keywords: actigraphy; cancer-related fatigue; insomnia; rest–activity cycle.

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    • Degradation of energy cost with fatigue induced by trail running: effect of distance

      Authors: Frederic Sabater Pastor, G Varesco, T Besson, J Koral, L Feasson, G Y Millet.

      Published: 05 March 2021 - Eur J Appl Physiol.


      Purpose: The effect of trail running competitions on cost of running (Cr) remains unclear and no study has directly examined the effect of distances in similar conditions on Cr. Accordingly, the aims of this study were to (i) assess the effect of trail running races of 40-170 km on Cr and (ii) to assess whether the incline at which Cr is measured influences changes in Cr.

      Methods: Twenty trail runners completed races of < 100 km (SHORT) and 26 trail runners completed races of > 100 km (LONG) on similar courses and environmental conditions. Oxygen uptake, respiratory exchange ratio, ventilation, and blood lactate were measured before and after the events on a treadmill with 0% (FLAT) and 15% incline (UH) and Cr was calculated.

      Results: Cr increased significantly after SHORT but not LONG races. There was no clear relationship between changes in Cr and changes in ventilation or blood lactate. There was a significant correlation (r = 0.75, p < 0.01) between changes in FLAT and UH Cr, and the change in Cr was not affected by the incline at which Cr was measured.

      Conclusion: The distance of the trail running race, but not the slope at which it is measured, influence the changes in Cr with fatigue. The mechanism by which Cr increases only in SHORT is not related to increased cost of breathing.

      Keywords: Cost of running; Fatigue; Running economy; Trail running.

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    • Time Course of Recovery after Cycling Repeated Sprints

      Authors: Fabio Milioni, Rafael A Azevedo, Alessandro M Zagatto, Guillaume Y Millet.

      Published: 01 February 2021 - Med Sci Sports Exerc.


      Purpose: The present study investigated the recovery of performance and neuromuscular fatigue after cycling repeated sprints.

      Methods: Ten participants performed two sessions of repeated sprints (one session: 10 × 10-s sprints, 30-s recovery) separated by 24 h (R24-S1 and R24-S2) and two sessions separated by 48 h (R48-S1 and R48-S2). The recovery condition (i.e., 24 or 48 h) was randomized and separated by 1 wk. All sessions were performed on a recumbent bike, allowing minimal delay between sprints termination and neuromuscular measurements. Neuromuscular function of knee extensors (neuromuscular assessment [NMA]) was assessed before sessions (presession), after the fifth sprint (midsession), and immediately after (postsession). Before sessions, baseline NMA was also carried out on an isometric chair. The NMA (bike and chair) was composed of maximal voluntary contraction (MVC) of knee extension and peripheral neuromuscular stimulation during the MVC and on relaxed muscle.

      Results: The sprints performance was not significantly different between sessions and did not presented significant interaction between recovery conditions. MVC was significantly lower at R24-S2 compared with R24-S1 (-6.5% ± 8.8%, P = 0.038) and R48-S2 (-5.6% ± 8.2%, P = 0.048), whereas resting potentiated high-frequency doublet (Db100) was lower at R24-S2 compared with R24-S1 (-10.4 ± 8.3, P = 0.01) (NMA on chair). There were significant reductions in MVC (>30%, P < 0.001) and Db100 (>38%, P < 0.001) from pre- to postsession in all sessions, without significant interactions between recovery conditions (NMA on bike).

      Conclusion: Cycling repeated sprints induce significant fatigue, particularly at the peripheral level, which is fully restored after 48 h, but not 24 h, of recovery. One versus two days of recovery does not affect neuromuscular fatigue appearance during cycling repeated-sprint sessions.

      Keywords: Fatigue; Central fatigue  Peripheral fatigue; Force ; Power; Performance.

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    • Do Sex Differences in Physiology Confer a Female Advantage in Ultra-Endurance Sport?

      Authors: Nicholas B Tiller, Kirsty J Elliott-Sale, Beat Knechtle, Patrick B Wilson, Justin D Roberts, Guillaume Y Millet.

      Published: 27 January 2021 - Sports Med.


      Ultra-endurance has been defined as any exercise bout that exceeds 6 h. A number of exceptional, record-breaking performances by female athletes in ultra-endurance sport have roused speculation that they might be predisposed to success in such events. Indeed, while the male-to-female performance gap in traditional endurance sport (e.g., marathon) remains at ~ 10%, the disparity in ultra-endurance competition has been reported as low as 4% despite the markedly lower number of female participants. Moreover, females generally outperform males in extreme-distance swimming. The issue is complex, however, with many sports-specific considerations and caveats. This review summarizes the sex-based differences in physiological functions and draws attention to those which likely determine success in extreme exercise endeavors. The aim is to provide a balanced discussion of the female versus male predisposition to ultra-endurance sport. Herein, we discuss sex-based differences in muscle morphology and fatigability, respiratory-neuromechanical function, substrate utilization, oxygen utilization, gastrointestinal structure and function, and hormonal control. The literature indicates that while females exhibit numerous phenotypes that would be expected to confer an advantage in ultra-endurance competition (e.g., greater fatigue resistance, greater substrate efficiency, and lower energetic demands), they also exhibit several characteristics that unequivocally impinge on performance (e.g., lower O2-carrying capacity, increased prevalence of GI distress, and sex-hormone effects on cellular function/injury risk). Crucially, the advantageous traits may only manifest as ergogenic in the extreme endurance events which, paradoxically, are those that females less often contest. The title question should be revisited in the coming years, when/if the number of female participants increases.

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    • Central Fatigue Aetiology in Prolonged Trail Running Races

      Authors: L Espeit, C G Brownstein, N Royer, T Besson, V Martin, G Y Millet, T Lapole.

      Published: 11 January 2021 - Revue


      New findings: What is the central question of this study? Are spinal and/or supraspinal perturbations implicated in central fatigue induced in the plantar flexor muscles following prolonged trail running races? What is the main finding and its importance? The present study confirmed the presence of central fatigue following various trail running distances from 40- to 170-km. The reduction in V-wave in conjunction with the lack of change in H-reflex suggests that a major component of this central fatigue may arise from supraspinal mechanisms in the plantar flexor muscles.

      Abstract: Trail running races are known to induce considerable impairments in neuromuscular function of which central mechanisms are a substantial component. However, the loci of this central fatigue (i.e. supraspinal and/or spinal) is not well identified. The aim of this study was to better understand central fatigue aetiology induced in the plantar flexor muscles by various trail running distances from 40- to 170-km. Eighteen runners participated in the study and neuromuscular function of their plantar flexors was tested before (PRE) and after (POST) various races during the Ultra-Trail du Mont Blanc. Neuromuscular function was evaluated with voluntary and evoked contractions using electrical tibial nerve stimulation. H-reflex and V-wave responses were also measured during submaximal and maximal voluntary contraction, respectively. Reductions in maximal voluntary contraction torque (-29%; p<0.001) and voluntary activation level (-12%; p<0.001) were observed after trail running races. V-wave was reduced in soleus (-35%; p = 0.003) and gastrocnemius medialis (-28%; p = 0.031), with no changes for H-reflex in soleus (p = 0.577). The present study confirmed the presence of central fatigue following trail running exercise. The reduction in V-wave in conjunction with the lack of change in H-reflex suggests that a major component of this central fatigue may arise from supraspinal mechanisms. This article is protected by copyright. All rights reserved.

      Keywords: H-reflex; V-wave; central fatigue; trail running.

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