title: Longitudinal changes in cardiorespiratory fitness: measurement error or true change?
abstract: OBJECTIVE
  This study examined the thesis that the reported Aerobics Center Longitudinal Study (ACLS) mortality reductions associated with improved cardiorespiratory fitness were because of measurement error of serial treadmill tests. We tested the research hypothesis that longitudinal changes in cardiorespiratory fitness of the ACLS cohort were a multivariate function of changes in self-report physical activity (SR-PA), resting heart rate, and body mass index (BMI).
  
  
  METHODS
  We used the results of three serial maximal treadmill tests (T1, T2, and T3) to evaluate the serial changes in cardiorespiratory fitness of 4675 men. The mean duration between the three serial tests examined was: T2 - T1, 1.9 yr; T3 - T2, 6.1 yr; and T3 - T1, 8.0 yr. Maximum and resting heart rate, BMI, SR-PA, and maximum Balke treadmill duration were measured on each occasion.
  
  
  RESULTS
  General linear models analysis showed that with change in maximum heart rate statistically controlled change in treadmill time performance was a function of independent changes in SR-PA, BMI, and R-HR. These variables accounted for significant (P < 0.001) proportions (7%, 9%, and 12%) of the change in treadmill time variance. Those men who increased their SR-PA and lowered their BMI and resting heart rate gained the most fitness between serial tests.
  
  
  CONCLUSIONS
  These results support the research hypothesis tested. Variations in serial ACLS treadmill tests are not just due to measurement error alone, but also to systematic variation linked with changes in lifestyle.
authors.affiliation: Department of Health and Human Performance, University of Houston, Houston, TX 77204, USA. AJackson@Mail.uh.edu
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Jackson
authors.forename: James B
authors.initials: JB
authors.lastname: Kampert
authors.forename: Carolyn E
authors.initials: CE
authors.lastname: Barlow
authors.forename: James R
authors.initials: JR
authors.lastname: Morrow
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Church
authors.forename: Steven N
authors.initials: SN
authors.lastname: Blair
mesh_terms: D000328:Adult; D015992:Body Mass Index; D002320:Cardiovascular Physiological Phenomena; D006801:Humans; D008019:Life Style; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010809:Physical Fitness / Q000502:physiology*; D012143:Respiratory Physiological Phenomena; D012650:Self Disclosure