title: The interactive effect of cooling and hypoxia on forearm fatigue development.
abstract: OBJECTIVE
  To examine the effect of separate and combined exposure to hypoxia [normoxia (FIO2 = 0.21) vs. moderate altitude (FIO2 = 0.13)] and temperature [thermoneutral (22 °C) vs. cold (5 °C)] on muscle fatigue development in the forearm, after repeated low-resistance contractions.
  
  
  METHODS
  Eight males were exposed for 70 min to four separate conditions in a balanced order. Conditions were normoxic-thermoneutral (N), hypoxic-thermoneutral, normoxic-cold and hypoxic-cold. After 15-min seated rest, participants carried out intermittent dynamic forearm exercise at 15 % maximal isometric voluntary contraction (MVC) for eight consecutive, 5-min work bouts. Each bout was separated by 110 s rest during which MVC force was collected.
  
  
  RESULTS
  When exposed to hypoxia and cold independently, the exercise protocol decreased MVC force of the finger flexors by 8.1 and 13.9 %, respectively, compared to thermoneutral normoxia. When hypoxia and cold were combined, the decrease in MVC force was 21.4 % more than thermoneutral normoxia, reflecting an additive effect and no interaction. EMG relative to force produced during MVC, increased by 2 and 1.2 μV per kg (36 and 23 % of N) for cold and hypoxia, respectively. When the stressors were combined the effect was additive, increasing to 3.1 μV per kg (56 % of N).
  
  
  CONCLUSIONS
  When compared to exercise in thermoneutral normoxic conditions, both cold and hypoxia significantly reduce brief MVC force output. This effect appears to be of mechanical origin, not a failure in muscle fibre recruitment per se. Additionally, the reduction in force is greater when the stressors are combined, showing an additive effect.
authors.affiliation: Environmental Ergonomics Research Centre, Loughborough University, James France Bldg, Loughborough, Leicestershire, LE11 2TU, UK.
authors.forename: Alex
authors.initials: A
authors.lastname: Lloyd
authors.forename: Simon
authors.initials: S
authors.lastname: Hodder
authors.forename: George
authors.initials: G
authors.lastname: Havenith
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D003080:Cold Temperature; D005542:Forearm / Q000503:physiopathology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007537:Isometric Contraction; D008297:Male; D018763:Muscle Fatigue; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000503:physiopathology*