title: Characterizing differences in mortality at the low end of the fitness spectrum.
abstract: OBJECTIVE
  A graded nonlinear relationship exists between fitness and mortality with the most remarkable difference in mortality rates observed between the least-fit (first, Q1) and the next-least-fit (second, Q2) quintile of fitness. The purpose of this study was to compare clinical characteristics, exercise test responses, and physical activity patterns in Q1 versus Q2 in apparently healthy individuals.
  
  
  METHODS
  A total of 4384 subjects referred for clinical treadmill testing from 1986 to 2006 were followed for a mean +/- SD period of 8.7 +/- 5.3 yr. All subjects had normal exercise ECG responses and no history of cardiovascular disease. Subjects were classified into quintiles of exercise capacity measured in METs. Clinical characteristics, physical activity patterns, and treadmill test results were compared between the first two quintiles (Q1: METs <5.9 (n = 693); Q2: METs 6.0-7.9 (n = 842)).
  
  
  RESULTS
  Small differences in age (64 +/- 11 vs 60 +/- 10 yr, P < 0.001), use of antihypertensive medications, prevalence of diabetes (21% vs 16%, P = 0.02), and dyslipidemia (43% vs 49%, P = 0.04) were observed between Q1 and Q2. When the Cox proportional hazards model was adjusted for age and other clinical characteristics, the relative risk of mortality remained almost two times greater in Q1 versus Q2 (cardiovascular mortality: HR: 4.01 vs 2.01, P < 0.001; reference group: fittest subjects (Q5)). In a subset of 802 subjects, recent recreational physical activity was significantly lower in Q1 versus Q2.
  
  
  CONCLUSIONS
  Reduced physical activity patterns rather than differences in clinical characteristics contribute to the striking difference in mortality rates between the least-fit and the next-least-fit quintile of fitness in healthy individuals.
authors: Veterans Affairs Palo Alto Health Care System, Palo Alto, CA, USA. sandra.mandic@otago.ac.nz
authors: Sandra
authors: S
authors: Mandic
authors: Jonathan N
authors: JN
authors: Myers
authors: Ricardo B
authors: RB
authors: Oliveira
authors: Joshua P
authors: JP
authors: Abella
authors: Victor F
authors: VF
authors: Froelicher
mesh_terms: D000368:Aged; D002140:California / Q000453:epidemiology; D005080:Exercise Test; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality / Q000639:trends*; D010809:Physical Fitness; D011379:Prognosis; D016016:Proportional Hazards Models; D011795:Surveys and Questionnaires