title: The effect of different volumes of high-intensity interval training on proinsulin in participants with the metabolic syndrome: a randomised trial.
abstract: The continuous demand for insulin in the face of insulin resistance, coupled with the glucolipotoxic environment associated with the metabolic syndrome (MetS), adversely affects the quality of insulin produced and secreted by the pancreatic beta cells. This is depicted by increased circulating intact proinsulin concentration, which is associated with increased MetS severity and risk of cardiovascular (CV) mortality. High-intensity interval training (HIIT) has been shown to reduce insulin resistance and other CV disease risk factors to a greater degree than moderate-intensity continuous training (MICT). We therefore aimed to investigate the impact of MICT and different volumes of HIIT on circulating intact proinsulin concentration.
  
  
  
  This was a substudy of the 'Exercise in prevention of Metabolic Syndrome' (EX-MET) multicentre trial. Sixty-six individuals with MetS were randomised to 16 weeks of: (1) MICT (n = 21, 30 min at 60-70% peak heart rate [HRpeak], five times/week); (2) 4HIIT (n = 22, 4 × 4 min bouts at 85-95% HRpeak, interspersed with 3 min of active recovery at 50-70% HRpeak, three times/week); or (3) 1HIIT (n = 23, 1 × 4 min bout at 85-95% HRpeak, three times/week). A subanalysis investigated the differential impact of these training programmes on intact proinsulin concentration in MetS individuals with type 2 diabetes (MICT, n = 6; 4HIIT, n = 9; 1HIIT, n = 12) and without type 2 diabetes (MICT, n = 15; 4HIIT, n = 13; 1HIIT, n = 11). Intact proinsulin, insulin and C-peptide concentrations were measured in duplicate via ELISA, following a 12 h fast, before and after the exercise programme. Fasting intact proinsulin concentration was also expressed relative to insulin and C-peptide concentrations.
  
  
  
  Following the exercise training, there were no significant (p > 0.05) changes in fasting intact proinsulin concentration indices in all participants (pre- vs post-programme proinsulin, proinsulin:insulin, proinsulin:C-peptide: MICT 19% decrease, 6% increase, 4% increase; 4HIIT 19% decrease, 8% decrease, 11% decrease; 1HIIT 34% increase, 49% increase, 36% increase). In participants who did not have type 2 diabetes, only 4HIIT significantly (p < 0.05) reduced fasting intact proinsulin concentration indices from pre to post intervention (pre- vs post-programme proinsulin, proinsulin:insulin, proinsulin:C-peptide: 4HIIT 32% decrease, 26% decrease, 32% decrease, p < 0.05; 1HIIT, 14% increase, 32% increase, 16% increase, p > 0.05; MICT 27% decrease, 17% decrease, 11% decrease), with a group × time interaction effect, indicating a greater reduction in intact proinsulin indices following 4HIIT compared with MICT and 1HIIT. There were no significant (p > 0.05) changes in intact proinsulin concentration indices in participants with type 2 diabetes.
  
  
  
  Higher-volume HIIT (4HIIT) improved insulin quality in MetS participants without type 2 diabetes.
  
  
  
  ClinicalTrials.gov NCT01676870 FUNDING: The study was funded by the Norwegian University of Science and Technology and from an unrestricted research grant from the Coca-Cola company. Funding for the collection of physical activity data was derived from a 'UQ New Staff Start Up' grant awarded to B. Clark.
authors.affiliation: Centre for Research on Exercise, Physical Activity and Health, School of Human Movement and Nutrition Sciences, The University of Queensland, Blair Drive, St Lucia, QLD, Australia.
authors.forename: Joyce S
authors.initials: JS
authors.lastname: Ramos
authors.affiliation: Recreation, Exercise, and Sport Science Department, Western State Colorado University, Gunnison, CO, USA.
authors.forename: Lance C
authors.initials: LC
authors.lastname: Dalleck
authors.affiliation: Institut des Sciences du Sport de l'Université de Lausanne (ISSUL), University of Lausanne, Lausanne, Switzerland.|Department of Physiology, Faculty of Biology and Medicine, Lausanne University, Lausanne, Switzerland.
authors.forename: Fabio
authors.initials: F
authors.lastname: Borrani
authors.affiliation: Centre for Research on Exercise, Physical Activity and Health, School of Human Movement and Nutrition Sciences, The University of Queensland, Blair Drive, St Lucia, QLD, Australia.
authors.forename: Alistair R
authors.initials: AR
authors.lastname: Mallard
authors.affiliation: School of Public Health, Faculty of Medicine and Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia.
authors.forename: Bronwyn
authors.initials: B
authors.lastname: Clark
authors.affiliation: Centre for Research on Exercise, Physical Activity and Health, School of Human Movement and Nutrition Sciences, The University of Queensland, Blair Drive, St Lucia, QLD, Australia.
authors.forename: Shelley E
authors.initials: SE
authors.lastname: Keating
authors.affiliation: Centre for Research on Exercise, Physical Activity and Health, School of Human Movement and Nutrition Sciences, The University of Queensland, Blair Drive, St Lucia, QLD, Australia.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Fassett
authors.affiliation: Centre for Research on Exercise, Physical Activity and Health, School of Human Movement and Nutrition Sciences, The University of Queensland, Blair Drive, St Lucia, QLD, Australia. jcoombes@uq.edu.au.
authors.forename: Jeff S
authors.initials: JS
authors.lastname: Coombes
mesh_terms: D000368:Aged; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition / Q000502:physiology; D002318:Cardiovascular Diseases / Q000517:prevention & control; D005260:Female; D000072696:High-Intensity Interval Training / Q000379:methods*; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology; D050417:Insulin-Secreting Cells / Q000378:metabolism; D008297:Male; D024821:Metabolic Syndrome / Q000097:blood*; D008875:Middle Aged; D011384:Proinsulin / Q000097:blood*; D012307:Risk Factors
chemical_list: D001786:Blood Glucose; D011384:Proinsulin
keywords: Glycaemic control; Insulin resistance; Interval training; Pancreatic beta cell function; Proinsulin