title: Clinical outcomes and cardiovascular responses to different exercise training intensities in patients with heart failure: a systematic review and meta-analysis.
abstract: OBJECTIVE
  The aim of this study was to establish whether aerobic exercise training intensity produces different effect sizes for fitness, adherence, event rates, mortality rates, and hospitalization rates in patients with heart failure.
  
  
  BACKGROUND
  Intuitively, greater exercise intensity is considered to result in higher risk for serious events, but intensity may be the primary stimulus for physical adaptation.
  
  
  METHODS
  A MEDLINE search (1985 to 2012) was conducted for exercise-based rehabilitation trials in heart failure, using the search terms "exercise training," "left ventricular dysfunction," "peak Vo2," "cardio-myopathy," and "systolic heart dysfunction." Seventy-four studies were included, producing 76 intervention groups; 9 (11.8%) were high-intensity, 38 (50%) vigorous-intensity, 24 (31.6%) moderate-intensity, and 5 (6.6%) low-intensity groups, providing a total of 3,265 exercising subjects and 2,612 control subjects.
  
  
  RESULTS
  Peak oxygen consumption increased by a mean difference of 3.33 ml·kg(-1)·min(-1) (95% confidence interval [CI]: 0.53 to 6.13 ml·kg(-1)·min(-1); p = 0.02) with high-intensity training in exercise groups compared with control groups, equating to a 23% improvement from baseline. For vigorous intensity, the mean difference was 2.27 ml·kg(-1)·min(-1) (95% CI: 1.70 to 2.84 ml·kg(-1)·min(-1); p < 0.00001), with an 8% weighted mean; for moderate intensity, the mean difference was 2.17 ml·kg(-1)·min(-1) (95% CI: 1.34 to 2.99 ml·kg(-1)·min(-1); p < 0.00001), with a weighted mean of 13%; and for low intensity, the mean difference was 1.04 ml·kg(-1)·min(-1) (95% CI: -2.50 to 4.57 ml·kg(-1)·min(-1); p = 0.57), with a weighted mean of 7%. In 123,479 patient-hours of training, not a single death was directly attributable to exercise.
  
  
  CONCLUSIONS
  As exercise training intensity rises, so may the magnitude of improvement in cardiorespiratory fitness, accompanied by lower study withdrawal in exercising patients. Total exercise time may be a confounder.
authors.affiliation: School of Science and Technology, University of New England, Armidale, Australia.
authors.forename: Hashbullah
authors.initials: H
authors.lastname: Ismail
authors.affiliation: School of Science and Technology, University of New England, Armidale, Australia.
authors.forename: James R
authors.initials: JR
authors.lastname: McFarlane
authors.affiliation: School of Science and Technology, University of New England, Armidale, Australia.
authors.forename: A Hadi
authors.initials: AH
authors.lastname: Nojoumian
authors.affiliation: School of Science and Technology, University of New England, Armidale, Australia.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Dieberg
authors.affiliation: School of Science and Technology, University of New England, Armidale, Australia. Electronic address: nsmart2@une.edu.au.
authors.forename: Neil A
authors.initials: NA
authors.lastname: Smart
mesh_terms: D005081:Exercise Therapy / Q000009:adverse effects / Q000379:methods*; D006333:Heart Failure / Q000503:physiopathology / Q000628:therapy*; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D010101:Oxygen Consumption / Q000502:physiology; D016032:Randomized Controlled Trials as Topic; D016896:Treatment Outcome
keywords: cardiorespiratory fitness; exercise intensity; heart failure; hospitalization; mortality