title: Irisin does not mediate resistance training-induced alterations in resting metabolic rate.
abstract: OBJECTIVE
  This study aimed to investigate the effects of a 6-month preventive resistance training program on resting metabolic rate (RMR) and its associations with fat-free mass (FFM) and the newly described myokine irisin as two potential mechanistic links between exercise training and RMR.
  
  
  METHODS
  In a randomized controlled trial, 74 sedentary healthy male and female participants either completed 6 months of high-repetition resistance training 3 d·wk in accordance with the American College of Sports Medicine recommendations (RT: n = 37; 47 ± 7 yr; body mass index, 25.0 ± 3.4 kg·m) or served as controls (CO: n = 37; 50 ± 7 yr; body mass index, 24.2 ± 3.2 kg·m). Strength (one-repetition maximum), RMR (indirect calorimetry), body fat (caliper method), and serum irisin concentration (enzyme-linked immunosorbent assay) were measured before and after 6 months of training.
  
  
  RESULTS
  Training led to an increase in strength (one-repetition maximum leg press, 16% ± 7%; P < 0.001). RMR increased in RT (1671 ± 356 vs 1843 ± 385 kcal·d, P < 0.001) but not in CO (1587 ± 285 vs 1602 ± 294 kcal·d, P = 0.97; group-time interaction, P < 0.01). Body weight (RT, -0.5 ± 2.4 kg; CO, 0.1 ± 2.3 kg), body fat percentage (RT, -1.1% ± 2.5%; CO, -0.7% ± 2.9%), and FFM (RT, 0.4 ± 2.1 kg; CO, 0.6 ± 1.9 kg) did not develop differently between groups (group-time interaction: P = 0.29, P = 0.54, and P = 0.59, respectively). Serum irisin concentration increased in CO (70.8 ± 83.4 ng·mL, P < 0.001) but not in RT (22.4 ± 92.6 ng·mL, P = 0.67; group-time interaction, P < 0.01). The change in RMR was not associated with the change in FFM (r = -0.11, P = 0.36) or irisin (r = -0.004, P = 0.97).
  
  
  CONCLUSIONS
  Preventive resistance training elicits an increase in RMR. However, in contrast to currently discussed hypotheses, this increase does not seem to be mediated by training-induced changes in FFM or circulating irisin concentration, which casts doubt in the meaning of irisin for human energy balance.
authors.affiliation: 1Department of Medical Oncology, National Center for Tumor Diseases (NCT), Heidelberg University Hospital, Heidelberg, GERMANY; 2German University of Applied Sciences for Prevention and Health Management, Saarbrücken, GERMANY; 3Institute of Sports and Preventive Medicine, Saarland University, Saarbrücken, GERMANY; and 4Institute for Molecular Cell Biology, Saarland University, Homburg, GERMANY.
authors.forename: Friederike
authors.initials: F
authors.lastname: Scharhag-Rosenberger
authors.forename: Tim
authors.initials: T
authors.lastname: Meyer
authors.forename: Melissa
authors.initials: M
authors.lastname: Wegmann
authors.forename: Sandra
authors.initials: S
authors.lastname: Ruppenthal
authors.forename: Lars
authors.initials: L
authors.lastname: Kaestner
authors.forename: Arne
authors.initials: A
authors.lastname: Morsch
authors.forename: Anne
authors.initials: A
authors.lastname: Hecksteden
mesh_terms: D050154:Adiposity; D000328:Adult; D000704:Analysis of Variance; D001481:Basal Metabolism / Q000502:physiology*; D001835:Body Weight; D002149:Energy Intake; D005260:Female; D005353:Fibronectins / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000502:physiology; D055070:Resistance Training; D057185:Sedentary Behavior
chemical_list: C577593:FNDC5 protein, human; D005353:Fibronectins