Aerobic Exercise, Training Dose, and Cardiorespiratory Fitness: Effects and Relationships with Resting Plasma Neurotrophic Factors in Alzheimer’s Dementia

Background: Vascular health is increasingly recognized for its roles in the pathogenesis and progression of Alzheimer’s disease (AD). The objective of this study was to investigate effects of exercise training, dose, and cardiorespiratory fitness (CRF) on neurotrophic factors in community-dwelling, older adults with mild-to-moderate AD dementia. Methods: This was a pilot blood ancillary study of the FIT-AD trial. Participants in the parent study were randomized to 6-month aerobic exercise (AEx) or stretching control. For this ancillary study, resting plasma brain-derived neurotrophic factor (BDNF), irisin, fibroblast growth factor-21 (FGF-21), and insulin-like growth factor-1 (IGF-1) biomarkers were assessed at baseline, 3, and 6 months. Estimates of within- and between- group effect sizes were calculated (Cohen’s d). Relationships of biomarker change with dose and CRF change were explored with multivariable linear regression and repeated measures correlations. Results: The sample (n = 26, 18 AEx/8 stretching) averaged 77.6 ± 6.9 years old, with the majority being male (65.4%), and non-Hispanic White (92.3%); between-group effect sizes were generally small except for irisin (d = −0.44)), AEx group relative to stretching group. Associations of dose and changes in CRF with changes in neurotrophic biomarker were weak (r² ≤ 0.025). Conclusions: The effects of exercise on BDNF, irisin, IGF-1, and FGF-21 were heterogeneous in AD. Our findings need validation in future, adequately powered exercise studies in AD.