title: Self-reported physical activity and objective aerobic fitness: differential associations with gray matter density in healthy aging.
abstract: Aerobic fitness (AF) and self-reported physical activity (srPA) do not represent the same construct. However, many exercise and brain aging studies interchangeably use AF and srPA measures, which may be problematic with regards to how these metrics are associated with brain outcomes, such as morphology. If AF and PA measures captured the same phenomena, regional brain volumes associated with these measures should directly overlap. This study employed the general linear model to examine the differential association between objectively-measured AF (treadmill assessment) and srPA (questionnaire) with gray matter density (GMd) in 29 cognitively unimpaired community-dwelling older adults using voxel based morphometry. The results show significant regional variance in terms of GMd when comparing AF and srPA as predictors. Higher AF was associated with greater GMd in the cerebellum only, while srPA displayed positive associations with GMd in occipito-temporal, left perisylvian, and frontal regions after correcting for age. Importantly, only AF level, and not srPA, modified the relationship between age and GMd, such that higher levels of AF were associated with increased GMd in older age, while decreased GMd was seen in those with lower AF as a function of age. These results support existing literature suggesting that both AF and PA exert beneficial effects on GMd, but only AF served as a buffer against age-related GMd loss. Furthermore, these results highlight the need for use of objective PA measurement and comparability of tools across studies, since results vary dependent upon the measures used and whether these are objective or subjective in nature.
authors.affiliation: Department of Psychiatry, Stein Institute for Research on Aging, University of California San Diego, La Jolla, CA, USA.
authors.forename: Zvinka Z
authors.initials: ZZ
authors.lastname: Zlatar
authors.affiliation: Department of Neurology, Emory University Atlanta, GA, USA ; Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Medical Center Decatur, GA, USA.
authors.forename: Keith M
authors.initials: KM
authors.lastname: McGregor
authors.affiliation: Department of Neurology, Emory University Atlanta, GA, USA ; Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Medical Center Decatur, GA, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Towler
authors.affiliation: Department of Neurology, Emory University Atlanta, GA, USA ; Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Medical Center Decatur, GA, USA.
authors.forename: Joe R
authors.initials: JR
authors.lastname: Nocera
authors.affiliation: Geriatric Research, Education and Clinical Center, VA Greater Los Angeles Healthcare System Los Angeles, CA, USA ; David Geffen School of Medicine, University of California, Los Angeles Los Angeles, CA, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Dzierzewski
authors.affiliation: Department of Neurology, Emory University Atlanta, GA, USA ; Center for Visual and Neurocognitive Rehabilitation, Atlanta VA Medical Center Decatur, GA, USA ; Department of Psychology, Georgia State University Atlanta, GA, USA.
authors.forename: Bruce
authors.initials: B
authors.lastname: Crosson
keywords: MRI; aerobic fitness; gray matter density; healthy aging; physical activity; voxel based morphometry