title: Markers of muscle damage and performance recovery after exercise in the heat.
abstract: OBJECTIVE
  This study aimed to determine whether competitive intermittent exercise in the heat affects recovery, aggravates markers of muscle fiber damage, and delays the recovery of performance and muscle glycogen stores.
  
  
  METHODS
  Plasma creatine kinase, serum myoglobin, muscle glycogen, and performance parameters (sprint, endurance, and neuromuscular testing) were evaluated in 17 semiprofessional soccer players before, immediately after, and during 48 h of recovery from a match played in 43°C (HOT) and compared with a control match (21°C with similar turf and setup).
  
  
  RESULTS
  Muscle temperature was ∼1°C higher (P < 0.001) after the game in HOT compared with control and reached individual values between 39.9°C and 41.1°C. Serum myoglobin levels increased by more than threefold after the matches (P < 0.01), but values were not different in HOT compared with control, and they were similar to baseline values after 24 h of recovery. Creatine kinase was significantly elevated both immediately and 24 h after the matches, but the response after HOT was reduced compared with control. Muscle glycogen responses were similar across trials and remained depressed for more than 48 h after both matches. Sprint performance and voluntary muscle activation were impaired to a similar extent after the matches (sprint by ∼2% and voluntary activation by ∼1.5%; P < 0.05). Both of these performance parameters as well as intermittent endurance capacity (estimated by a Yo-Yo IR1 test) were fully recovered 48 h after both matches.
  
  
  CONCLUSIONS
  Environmental heat stress does not aggravate the recovery response from competitive intermittent exercise associated with elevated muscle temperatures and markers of muscle damage, delayed resynthesis of muscle glycogen, and impaired postmatch performance.
authors.affiliation: Department of Exercise and Sport Sciences, University of Copenhagen, Denmark. lnnielsen@ifi.ku.dk
authors.forename: Lars
authors.initials: L
authors.lastname: Nybo
authors.forename: Olivier
authors.initials: O
authors.lastname: Girard
authors.forename: Magni
authors.initials: M
authors.lastname: Mohr
authors.forename: Wade
authors.initials: W
authors.lastname: Knez
authors.forename: Sven
authors.initials: S
authors.lastname: Voss
authors.forename: Sebastien
authors.initials: S
authors.lastname: Racinais
mesh_terms: D000328:Adult; D003402:Creatine Kinase / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006003:Glycogen / Q000032:analysis; D006358:Hot Temperature; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology / Q000502:physiology*; D009211:Myoglobin / Q000097:blood; D010807:Physical Endurance / Q000502:physiology; D012916:Soccer / Q000502:physiology*
chemical_list: D009211:Myoglobin; D006003:Glycogen; D003402:Creatine Kinase