title: Cardiorespiratory fitness is associated with white matter integrity in aging.
abstract: OBJECTIVE
  Aging is associated with reduced neural integrity, yet there are remarkable individual differences in brain health among older adults (OA). One factor that may attenuate age-related neural decline is cardiorespiratory fitness (CRF). The primary aim of this study was to link CRF to neural white matter microstructure using diffusion tensor imaging in OA.
  
  
  METHODS
  Young adults (YA; n = 32) and OA (n = 27) completed a graded maximal exercise test to evaluate CRF and diffusion tensor magnetic resonance imaging to examine neural white matter integrity.
  
  
  RESULTS
  As expected, pervasive age-related declines in white matter integrity were observed when OA were compared to YA. Further, peak VO2 was positively associated with fractional anisotropy (FA), an indicator of white matter integrity, in multiple brain regions in OA, but not YA. In multiple posterior regions such as the splenium, sagittal stratum, posterior corona radiata, and superior parietal white matter, FA values were similar in YA and OA classified as higher fit, with both groups having greater FA than lower fit OA. However, age-related differences in FA values remained in other regions, including the body and genu of the corpus callosum, precuneus, and superior frontal gyrus.
  
  
  CONCLUSIONS
  CRF is positively associated with neural white matter microstructure in aging. The relationship between peak VO2 and FA appears to be tract-specific, as equivalent FA values were observed in higher fit OA and YA in some white matter tracts, but not others. Further, the association between peak VO2 and FA appears to be age-dependent.
authors.affiliation: Memory Disorders Research Center, VA Boston Healthcare System and Boston University School of Medicine Boston, Massachusetts ; Neuroimaging Research for Veterans Center, VA Boston Healthcare System Boston, Massachusetts.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Hayes
authors.affiliation: Neuroimaging Research for Veterans Center, VA Boston Healthcare System Boston, Massachusetts ; Athinoula A. Martinos Center for Biomedical Imaging, MGH Radiology Charlestown, Massachusetts.
authors.forename: David H
authors.initials: DH
authors.lastname: Salat
authors.affiliation: Geriatric Research, Education, and Clinical Center, VA Pittsburgh Healthcare System Pittsburgh, Pennsylvania ; Geriatric Cardiology Section, University of Pittsburgh Medical Center Pittsburgh, Pennsylvania.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Forman
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, MGH Radiology Charlestown, Massachusetts ; Department of Neurology, Massachusetts General Hospital Boston, Massachusetts ; Harvard Medical School Boston, Massachusetts ; Center of Alzheimer's Research and Treatment, Department of Neurology, Brigham and Women's Hospital Boston, Massachusetts.
authors.forename: Reisa A
authors.initials: RA
authors.lastname: Sperling
authors.affiliation: Memory Disorders Research Center, VA Boston Healthcare System and Boston University School of Medicine Boston, Massachusetts.
authors.forename: Mieke
authors.initials: M
authors.lastname: Verfaellie