title: High-intensity interval training (HIIT) increases insulin-like growth factor-I (IGF-I) in sedentary aging men but not masters' athletes: an observational study.
abstract: BACKGROUND
  The aim of this investigation was to examine the impact high-intensity interval training (HIIT) on serum insulin-like growth factor-I (IGF-I) in active compared with sedentary aging men.
  
  
  METHODS
  22 lifetime sedentary (SED; 62 ± 2 years) and 17 masters' athletes (LEX; 60 ± 5 years) were recruited to the study. As HIIT requires preconditioning exercise in sedentary cohorts, the study required three assessment phases; enrollment (phase A), following preconditioning exercise (phase B), and post-HIIT (phase C). Serum IGF-I was determined by electrochemiluminescent immunoassay.
  
  
  RESULTS
  IGF-I was higher in LEX compared to SED at baseline (p = 0.007, Cohen's d = 0.91), and phase B (p = 0.083, Cohen's d = 0.59), with only a small difference at C (p = 0.291, Cohen's d = 0.35). SED experienced a small increase in IGF-I following preconditioning from 13.1 ± 4.7 to 14.2 ± 6.0 μg·dl-1(p = 0.376, Cohen's d = 0.22), followed by a larger increase post-HIIT (16.9 ± 4.4 μg·dl-1), which was significantly elevated compared with baseline (p = 0.002, Cohen's d = 0.85), and post-preconditioning (p = 0.005, Cohen's d = 0.51). LEX experienced a trivial changes in IGF-I from A to B (18.2 ± 6.4 to 17.2 ± 3.7 μg·dl-1[p = 0.538, Cohen's d = 0.19]), and a small change post-HIIT (18.4 ± 4.1 μg·dl-1[p = 0.283, Cohen's d = 0.31]). Small increases were observed in fat-free mass in both groups following HIIT (p < 0.05, Cohen's d = 0.32-0.45).
  
  
  CONCLUSIONS
  In conclusion, HIIT with preconditioning exercise abrogates the age associated difference in IGF-I between SED and LEX, and induces small improvements in fat-free mass in both SED and LEX.
authors.affiliation: a School of Sport, Health and Outdoor Education, Trinity Saint David, University of Wales , Carmarthen , UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Herbert
authors.affiliation: b Active Ageing Research Group, Department of Medical and Sport Sciences, University of Cumbria , Lancaster , UK.
authors.forename: Lawrence D
authors.initials: LD
authors.lastname: Hayes
authors.affiliation: c Institute of Clinical Exercise and Health Science, University of the West of Scotland , Hamilton , UK , and.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Sculthorpe
authors.affiliation: d Faculty of Health , Federation University , Ballarat , VIC , Australia.
authors.forename: Fergal M
authors.initials: FM
authors.lastname: Grace
mesh_terms: D056352:Athletes; D001823:Body Composition / Q000502:physiology; D000072696:High-Intensity Interval Training; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism*; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D057185:Sedentary Behavior
chemical_list: D007334:Insulin-Like Growth Factor I
keywords: Exercise; HIIT; IGF-I; growth hormone; training