title: Endurance training and maximal oxygen consumption with ageing: Role of maximal cardiac output and oxygen extraction.
abstract: BACKGROUND
  The increase in maximal oxygen consumption (VO2max) with endurance training is associated with that of maximal cardiac output (Qmax), but not oxygen extraction, in young individuals. Whether such a relationship is altered with ageing remains unclear. Therefore, we sought systematically to review and determine the effect of endurance training on and the associations among VO2max, Qmax and arteriovenous oxygen difference at maximal exercise (Ca-vO2max) in healthy aged individuals.
  
  
  METHODS
  We conducted a systematic search of MEDLINE, Scopus and Web of Science, from their inceptions until May 2015 for articles assessing the effect of endurance training lasting 3 weeks or longer on VO2max and Qmax and/or Ca-vO2max in healthy middle-aged and/or older individuals (mean age ≥40 years). Meta-analyses were performed to determine the standardised mean difference (SMD) in VO2max, Qmax and Ca-vO2max between post and pre-training measurements. Subgroup and meta-regression analyses were used to evaluate the associations among SMDs and potential moderating factors.
  
  
  RESULTS
  Sixteen studies were included after systematic review, comprising a total of 153 primarily untrained healthy middle-aged and older subjects (mean age 42-71 years). Endurance training programmes ranged from 8 to 52 weeks of duration. After data pooling, VO2max (SMD 0.89; P < 0.0001) and Qmax (SMD 0.61; P < 0.0001) were increased after endurance training; no heterogeneity among studies was detected. Ca-vO2max was only increased with endurance training interventions lasting more than 12 weeks (SMD 0.62; P = 0.001). In meta-regression, the SMD in Qmax was positively associated with the SMD in VO2max (B = 0.79, P = 0.04). The SMD in Ca-vO2max was not associated with the SMD in VO2max (B = 0.09, P = 0.84).
  
  
  CONCLUSIONS
  The improvement in VO2max following endurance training is a linear function of Qmax, but not Ca-vO2max, through healthy ageing.
authors.affiliation: Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Switzerland david.montero.barril@gmail.com.
authors.forename: David
authors.initials: D
authors.lastname: Montero
authors.affiliation: Center for Molecular Cardiology, University of Zurich, Switzerland.
authors.forename: Candela
authors.initials: C
authors.lastname: Díaz-Cañestro
mesh_terms: D000375:Aging / Q000378:metabolism*; D002302:Cardiac Output / Q000502:physiology*; D006801:Humans; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D010807:Physical Endurance / Q000502:physiology*
chemical_list: D010100:Oxygen
keywords: Exercise training; ageing; maximal oxygen consumption; meta-analysis