title: Irisin in blood increases transiently after single sessions of intense endurance exercise and heavy strength training.
abstract: OBJECTIVE
  Irisin is a recently identified exercise-induced hormone that increases energy expenditure, at least in rodents. The main purpose of this study was to test the hypothesis that Irisin increases acutely in blood after singular sessions of intense endurance exercise (END) and heavy strength training (STR). Secondary, we wanted to explore the relationship between body composition and exercise-induced effects on irisin, and the effect of END and STR on muscular expression of the irisin gene FNDC5.
  
  
  METHODS
  Nine moderately trained healthy subjects performed three test days using a randomized and standardized crossover design: one day with 60 minutes of END, one day with 60 minutes of STR, and one day without exercise (CON). Venous blood was sampled over a period of 24h on the exercise days.
  
  
  RESULTS
  Both END and STR led to transient increases in irisin concentrations in blood, peaking immediately after END and one hour after STR, before gradually returning to baseline. Irisin responses to STR, but not END, showed a consistently strong negative correlation with proportions of lean body mass. Neither END nor STR affected expression of FNDC5, measured 4h after training sessions, though both protocols led to pronounced increases in PGC-1α expression, which is involved in transcriptional control of FNDC5.
  
  
  CONCLUSIONS
  The results strongly suggest that single sessions of intense endurance exercise and heavy strength training lead to transient increases in irisin concentrations in blood. This was not accompanied by increased FNDC5 expression, measured 4h post-exercise. The results suggest that irisin responses to resistance exercise are higher in individuals with lower proportions of lean body mass.
authors.affiliation: Lillehammer University College, Lillehammer, Norway.
authors.forename: Håvard
authors.initials: H
authors.lastname: Nygaard
authors.affiliation: Lillehammer University College, Lillehammer, Norway.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Slettaløkken
authors.affiliation: Lillehammer University College, Lillehammer, Norway.
authors.forename: Geir
authors.initials: G
authors.lastname: Vegge
authors.affiliation: Hospital for Rheumatic Diseases, Lillehammer, Norway.
authors.forename: Ivana
authors.initials: I
authors.lastname: Hollan
authors.affiliation: Innlandet Hospital Trust, Lillehammer, Norway.
authors.forename: Jon Elling
authors.initials: JE
authors.lastname: Whist
authors.affiliation: Innlandet Hospital Trust, Lillehammer, Norway.
authors.forename: Tor
authors.initials: T
authors.lastname: Strand
authors.affiliation: Lillehammer University College, Lillehammer, Norway.
authors.forename: Bent R
authors.initials: BR
authors.lastname: Rønnestad
authors.affiliation: Lillehammer University College, Lillehammer, Norway.
authors.forename: Stian
authors.initials: S
authors.lastname: Ellefsen
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005260:Female; D005353:Fibronectins / Q000097:blood*; D006801:Humans; D008297:Male; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010807:Physical Endurance / Q000502:physiology*; D014157:Transcription Factors / Q000096:biosynthesis
chemical_list: C577593:FNDC5 protein, human; D005353:Fibronectins; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D014157:Transcription Factors