title: Association between fatigue and failure to preserve cerebral energy turnover during prolonged exercise.
abstract: OBJECTIVE
  This study evaluated if the fatigue and apathy arising during exercise with hypoglycaemia could relate to a lowering of the cerebral metabolic rates of glucose and oxygen.
  
  
  RESULTS
  Six males completed 3 h of cycling with or without glucose supplementation in random order. Cerebral blood flow, metabolism and interleukin-6 (IL-6) release were evaluated with the Kety-Schmidt technique. Blood glucose was maintained during the glucose trial, while it decreased from 5.2 +/- 0.1 to 2.9 +/- 0.3 mmol L-1 (mean +/- SE) after 180 min of exercise in the placebo trial with a concomitant increase in perceived exertion (P < 0.05). During hypoglycaemia, the cerebral glucose uptake was reduced from 0.34 +/- 0.05 to 0.28 +/- 0.04 micromol g(-1) min(-1), while the cerebral uptake of beta-hydroxybutyrate increased to 5 +/- 1 pmol g(-1) min(-1) (P < 0.05). The reduced glucose uptake was accompanied by a lowering of the cerebral metabolic rate of oxygen from 1.84 +/- 0.19 mmol g(-1) min(-)1 during exercise with glucose supplementation to 1.60 +/- 0.16 mmol g(-1) min(-1) during hypoglycaemia (P < 0.05). In addition, the cerebral IL-6 release was reduced from 0.4 +/- 0.1 to 0.0 +/- 0.1 pg g(-1) min(-1) (P < 0.05).
  
  
  CONCLUSIONS
  Exercise-induced hypoglycaemia limits the cerebral uptake of glucose, exacerbates exercise, reduces the cerebral metabolic rate of oxygen and attenuates the release of IL-6 from the brain.
authors.affiliation: Department of Human Physiology, Institute of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Nybo
authors.forename: K
authors.initials: K
authors.lastname: Møller
authors.forename: B K
authors.initials: BK
authors.lastname: Pedersen
authors.forename: B
authors.initials: B
authors.lastname: Nielsen
authors.forename: N H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000378:metabolism; D000328:Adult; D000704:Analysis of Variance; D001786:Blood Glucose / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D002560:Cerebrovascular Circulation / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005221:Fatigue / Q000378:metabolism*; D005947:Glucose / Q000627:therapeutic use; D006801:Humans; D007003:Hypoglycemia / Q000378:metabolism / Q000517:prevention & control; D015850:Interleukin-6 / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology
chemical_list: D001786:Blood Glucose; D015850:Interleukin-6; D005947:Glucose; D020155:3-Hydroxybutyric Acid