title: Maximal cardiac output in athletes: influence of age.
abstract: BACKGROUND
  The decline in maximal oxygen consumption (VO2max) with age seems to be exacerbated in endurance-trained athletes (EA) relative to untrained healthy subjects. Whether maximal cardiac output (Qmax) parallels this group-specific decline with age remains uncertain. Therefore, we sought to systematically review the literature and determine whether Qmax is similarly enhanced in EA across all ages relative to age-matched untrained counterparts.
  
  
  METHODS
  We conducted a systematic search of MEDLINE, Cochrane and Web of Science from their inceptions until June 2014 for articles evaluating Qmax in athletes. A meta-analysis was performed to determine the standardized mean difference (SMD) in Qmax between EA and age-matched untrained healthy subjects. Included studies had to (i) comprise EA and control groups matched for body size or (ii) present Qmax values normalized for body size. Subgroup and meta-regression analyses were used to study the influence of age and potential moderating factors.
  
  
  RESULTS
  Eighteen studies were selected after systematic review, comprising 268 EA and 232 age-matched untrained subjects. Nine studies involved young EA (mean age ≤40 years) while nine studies involved master EA (mean age >55 years). After data pooling, young and master EA groups showed higher Qmax compared with control groups (SMD = 1.49 and SMD = 1.68, respectively; both p < 0.0001). The SMD in Qmax between EA and control groups was similar in studies in young EA compared with studies in master EA (p = 0.61). Moreover, the SMD in VO2max between EA and control groups did not differ in studies in young EA compared with studies in master EA (p = 0.37). In meta-regression analyses, the difference in percentage of body fat between EA and control groups was inversely associated with the SMD in Qmax (B = - 0.17, p = 0.01) and the SMD in VO2max (B = -0.20, p = 0.01). Mean age was not associated with the SMD in Qmax (B = -0.001, P = 0.90) nor with the SMD in VO2max (B = 0.01, P = 0.58).
  
  
  CONCLUSIONS
  Based on current published studies, the enhanced Qmax observed in EA compared with untrained healthy subjects matched for body size is not affected by age but may be related, at least in part, to the improved body composition of EA.
authors.affiliation: Department of Internal Medicine, Maastricht University Medical Centre (MUMC), the Netherlands Cardiovascular Research Institute Maastricht (CARIM), the Netherlands 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: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D056352:Athletes; D001823:Body Composition; D002302:Cardiac Output; D016009:Chi-Square Distribution; D005260:Female; D006321:Heart / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D010807:Physical Endurance; D055815:Young Adult
keywords: Endurance training; ageing; maximal cardiac output; maximal oxygen consumption