Cerebral Responses During Exercise in Hypoxia
Condition: Brain Hypoxia; Hypoxia
MeSH terms: Hypoxia, Brain; Hypoxia
Study type: Interventional

Summary: 
      While the exercise responses are classically described at the cardiorespiratory and muscle
      levels, recent data suggest that the brain is also significantly stressed by exercise and may
      even participate to performance limitation. In hypoxia in particular, cerebral responses to
      exercise may be altered and promote performance reduction during endurance exercise. In the
      present study, the investigators used innovative approaches to assess cerebral perturbations
      associated with exercise in hypoxia.
    

Detailed description: 
      In the classical paradigm of exercise physiology, cardio-respiratory capacity and muscle
      fatigue are though to set the limit of exercise tolerance. However, there are experimental
      situations where it is not possible to explain exercise performance limitation using this
      classical paradigm, and it is therefore necessary to look for an alternative. Recent
      investigations highlight changes associated with exercise in the brain, e.g. changes in
      cerebral perfusion, cerebral oxygenation and neuron excitability. Also, several results
      suggest that in some conditions, the central nervous system fails to drive the motoneurons
      adequately, i.e. the so called central fatigue. However, the phenomenon of central limitation
      to exercise and its underlying neurophysiological mechanisms are still to clarify. Cerebral
      metabolism and neurohumoral responses during fatiguing exercise are therefore to investigate
      in order to propose a new paradigm able to explain exercise limitation. Among the conditions
      where the classical paradigm of exercise performance limitation does not appear to suit the
      actual observations, exercise under hypoxic environment appears to be particularly
      challenging. Some data suggest indeed that the cerebral response to exercise may be
      substantially modified in hypoxia compared to normoxia.

      Hence, in the present project, the investigators aim to evaluate the effect of hypoxia on
      brain adaptation to exercise in healthy human. In particular, the objective is to assess the
      brain neurophysiological response to a fatiguing exercise, including cerebral perfusion and
      oxygenation, cerebral activation, cortical excitability as well as the resultant motor
      command while inhaling normoxic or hypoxic gas mixtures. To fulfil these objectives,
      complementary methodological approaches will be used during exercise both normoxic and
      hypoxic conditions: functional magnetic resonance imaging (fMRI) will be used to evaluate
      cerebral activation, the perfusion imaging arterial spin labelling (ASL) nuclear magnetic
      resonance method will assess regional cerebral perfusion, near infrared spectroscopy (NIRS)
      will allow measurement of cerebral oxygenation, measurement of motor evoked potential in
      response to transcranial magnetic stimulation (TMS) will assess the cortical excitability,
      measurement of the level of central activation (assessed by TMS) and the electromyographic
      (EMG) signals will evaluate the motor command. Moreover, to account for the effect of the
      muscle mass involved during exercise and the duration of hypoxic exposure, brain adaptation
      to exercise in hypoxia will be assessed for motor task involving small (thumb adduction) or
      large (knee extension, cycle ergometry) muscle groups as well as for acute (<1 hour) or
      prolonged hypoxic exposure (several hours: 6 hours). This multi-technical approach will be
      possible through this collaborative project between three partners experts in brain function
      investigation and exercise physiology (Institut Fédératif de Recherche 'RMN Biomédical et
      Neurosciences' Joseph Fourier University and University Hospital, Grenoble; 'Exercise
      Physiology' Laboratory, University Hospital, St Etienne; 'Motor Efficiency and Deficiency
      Laboratory', Montpellier I University, Montpellier).

      The investigators hypothesise that hypoxia would enhance the cerebral perturbation associated
      with a given fatiguing exercise, i.e. would induce greater reduction in cerebral blood and
      cerebral oxygenation, greater reduction in cortical excitability and central activation as
      well as larger reduction in central command, and this particularly when a large muscle mass
      is involved as well as when hypoxic exposure is prolonged.

      This project aims to renew our vision of the limitation of human exercise performance as well
      as our understanding of exercise tolerance under hypoxemic conditions. The later is relevant
      for sport and altitude medicine dealing with exercise and altitude tolerance, as well as for
      diseases characterised by hypoxemia and exercise intolerance such as respiratory diseases
      like chronic obstructive pulmonary diseases for example.
    

Intervention name(s): Hypoxic exposure
Intervention type(s): Other
Intervention description(s): Subjects breath either normoxic or hypoxic (FiO2 = 12%) gas mixture
Other intervention name(s): Hypoxia (FiO2 = 12%)
Intervention model: Single Group Assignment
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: Cerebral; Oxygenation; Performance; Exercise