title: Age-dependent prognostic value of exercise capacity and derivation of fitness-associated biologic age.
abstract: OBJECTIVE
  Given the aging population and prevalence of sedentary behaviour in the USA, we investigated the impact of differences in exercise capacity associated with age on long-term outcomes. We derived fitness-associated 'biologic age' as a tool to encourage positive lifestyle changes.
  
  
  METHODS
  This retrospective cohort study included 57085 patients without established coronary artery disease or heart failure (median age 53 years, 49% women, 29% black) who underwent clinically-referred treadmill stress testing at the Henry Ford Health System from 1991 to 2009. Patients were followed for 10.4±5 and 5.4±4 years for all-cause mortality and myocardial infarction (MI), respectively. We calculated hazard ratios associated with exercise capacity by age deciles using Cox regression models, adjusting for demographic and haemodynamic data, medical history, and medication use. Fitness-associated 'biologic age' was derived as the chronologic age with equivalent mortality or MI risk.
  
  
  RESULTS
  There were 6356 deaths and 1646 MIs during follow-up. Exercise capacity declined with increasing age. Higher exercise capacity was strongly associated with greater survival, with per-MET HR ranging from 0.82 (95% CI 0.78 to 0.86) in patients under 40 years of age, to 0.88 (95% CI 0.87 to 0.90) in those over 70 years of age. Biologic age varied markedly-up to three decades-within each age decile, and was a stronger predictor of mortality (C-statistic 0.81 vs 0.77) and MI (C-statistic 0.72 vs 0.68) than chronologic age.
  
  
  CONCLUSIONS
  Higher exercise capacity remained a powerful predictor of survival despite lower average exercise capacity at older ages, reinforcing its importance in patients of all ages. Fitness-associated biologic age was a stronger predictor of survival than chronologic age, and may be a useful clinical tool for facilitating patient discussions regarding the impact of exercise capacity on long-term risk.
authors.affiliation: Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, Baltimore, Maryland, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Blaha
authors.affiliation: Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, Baltimore, Maryland, USA.
authors.forename: Rupert K
authors.initials: RK
authors.lastname: Hung
authors.affiliation: Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, Baltimore, Maryland, USA.
authors.forename: Zeina
authors.initials: Z
authors.lastname: Dardari
authors.affiliation: Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, Baltimore, Maryland, USA.
authors.forename: David I
authors.initials: DI
authors.lastname: Feldman
authors.affiliation: Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, Baltimore, Maryland, USA.
authors.forename: Seamus P
authors.initials: SP
authors.lastname: Whelton
authors.affiliation: Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, Baltimore, Maryland, USA Center for Healthcare Advancement & Outcomes & Miami Cardiac & Vascular Institute (MCVI), Baptist Health South Florida, Miami, FL, USA, Henry Ford Hospital, Detroit, Michigan, USA.
authors.forename: Khurram
authors.initials: K
authors.lastname: Nasir
authors.affiliation: Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, Baltimore, Maryland, USA.
authors.forename: Roger S
authors.initials: RS
authors.lastname: Blumenthal
authors.affiliation: Division of Cardiovascular Medicine, Henry Ford Hospital, Detroit, Michigan, USA.
authors.forename: Clinton A
authors.initials: CA
authors.lastname: Brawner
authors.affiliation: Division of Cardiovascular Medicine, Henry Ford Hospital, Detroit, Michigan, USA.
authors.forename: Jonathan K
authors.initials: JK
authors.lastname: Ehrman
authors.affiliation: Division of Cardiovascular Medicine, Henry Ford Hospital, Detroit, Michigan, USA.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Keteyian
authors.affiliation: Division of Cardiovascular Medicine, Henry Ford Hospital, Detroit, Michigan, USA King Saud bin Abdulaziz University for Health Sciences, King Abdullah International Medical Research Center, King ABdulAziz Cardiac Center, Ministry of National Guard, Health Affairs, Saudia Arabia.
authors.forename: Mouaz H
authors.initials: MH
authors.lastname: Al-Mallah
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D002423:Cause of Death / Q000639:trends; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D015577:Geriatric Assessment; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000401:mortality / Q000503:physiopathology / Q000534:rehabilitation*; D010809:Physical Fitness / Q000502:physiology*; D011379:Prognosis; D012189:Retrospective Studies; D015996:Survival Rate / Q000639:trends; D013997:Time Factors; D014481:United States / Q000453:epidemiology