title: The impact of high-intensity interval training versus moderate-intensity continuous training on vascular function: a systematic review and meta-analysis.
abstract: BACKGROUND
  Vascular dysfunction is a precursor to the atherosclerotic cascade, significantly increasing susceptibility to cardiovascular events such as myocardial infarction or stroke. Previous studies have revealed a strong relationship between vascular function and cardiorespiratory fitness (CRF). Thus, since high-intensity interval training (HIIT) is a potent method of improving CRF, several small randomized trials have investigated the impact on vascular function of HIIT relative to moderate-intensity continuous training (MICT).
  
  
  OBJECTIVE
  The aim of this study was to systematically review the evidence and quantify the impact on vascular function of HIIT compared with MICT.
  
  
  METHODS
  Three electronic databases (PubMed, Embase, and MEDLINE) were searched (until May 2014) for randomized trials comparing the effect of at least 2 weeks of HIIT and MICT on vascular function. HIIT protocols involved predominantly aerobic exercise at a high intensity, interspersed with active or passive recovery periods. We performed a meta-analysis to compare the mean difference in the change in vascular function assessed via brachial artery flow-mediated dilation (FMD) from baseline to post-intervention between HIIT and MICT. The impact of HIIT versus MICT on CRF, traditional cardiovascular disease (CVD) risk factors, and biomarkers associated with vascular function (oxidative stress, inflammation, and insulin resistance) was also reviewed across included studies.
  
  
  RESULTS
  Seven randomized trials, including 182 patients, met the eligibility criteria and were included in the meta-analysis. A commonly used HIIT prescription was four intervals of 4 min (4 × 4 HIIT) at 85-95% of maximum or peak heart rate (HRmax/peak), interspersed with 3 min of active recovery at 60-70% HRmax/peak, three times per week for 12-16 weeks. Brachial artery FMD improved by 4.31 and 2.15% following HIIT and MICT, respectively. This resulted in a significant (p < 0.05) mean difference of 2.26%. HIIT also had a greater tendency than MICT to induce positive effects on secondary outcome measures, including CRF, traditional CVD risk factors, oxidative stress, inflammation, and insulin sensitivity.
  
  
  CONCLUSIONS
  HIIT is more effective at improving brachial artery vascular function than MICT, perhaps due to its tendency to positively influence CRF, traditional CVD risk factors, oxidative stress, inflammation, and insulin sensitivity. However, the variability in the secondary outcome measures, coupled with the small sample sizes in these studies, limits this finding. Nonetheless, this review suggests that 4 × 4 HIIT, three times per week for at least 12 weeks, is a powerful form of exercise to enhance vascular function.
authors.affiliation: School of Human Movement and Nutrition Sciences, The University of Queensland, Rm 535, HMNS Building, St Lucia, Brisbane, QLD, 4072, Australia.
authors.forename: Joyce S
authors.initials: JS
authors.lastname: Ramos
authors.forename: Lance C
authors.initials: LC
authors.lastname: Dalleck
authors.forename: Arnt Erik
authors.initials: AE
authors.lastname: Tjonna
authors.forename: Kassia S
authors.initials: KS
authors.lastname: Beetham
authors.forename: Jeff S
authors.initials: JS
authors.lastname: Coombes
mesh_terms: D001794:Blood Pressure / Q000502:physiology; D050218:Body Fat Distribution; D001916:Brachial Artery / Q000502:physiology; D002097:C-Reactive Protein / Q000032:analysis; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology; D008055:Lipids / Q000097:blood; D018384:Oxidative Stress / Q000502:physiology; D010101:Oxygen Consumption / Q000502:physiology; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010809:Physical Fitness / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology; D055070:Resistance Training / Q000379:methods*; D014157:Transcription Factors / Q000097:blood
chemical_list: D008055:Lipids; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D014157:Transcription Factors; D002097:C-Reactive Protein