Effects of high-intensity interval training with or without resistance training on Alzheimer's disease brain signatures in individuals with coronary artery disease: the Heart-Brain randomized controlled trial.

Background: Coronary artery disease (CAD) increases the risk of cognitive impairment, dementia, and brain structural alterations. This heart-brain connection suggests that exercise-induced cardiovascular responses may influence brain regions vulnerable to Alzheimer's disease (AD), the most common cause of dementia. This study aimed to examine the effects of 12-weeks of either high-intensity interval training (HIIT) plus resistance training (RT) or HIIT alone on AD brain signatures in individuals with CAD, to explore moderating factors, and to assess associations between changes in AD brain signatures and cognition and physical fitness. Methods: This secondary analysis of a single-site, three-arm, single-blinded randomized controlled trial included 105 individuals with CAD (50-75 years; 21% female) randomly allocated to HIIT+RT, HIIT, or usual care (UC) groups. T1- and diffusion-weighted magnetic resonance imaging were acquired before and after the 12-week intervention. Primary outcomes were thickness/volume and gray matter mean diffusivity (GMMD) signatures, derived from seven cortical regions and the hippocampus. Moderators included age, sex, education, and baseline AD brain signatures. Results: For the thickness/volume signature, no between-group differences in changes were observed between HIIT+RT and UC (+0.13 standardized mean difference [SMD]; 95% CI, -0.07 to 0.33) or between HIIT and UC (-0.1 SMD; 95% CI, -0.3 to 0.1); however, a small but significant between-group difference in change was found between HIIT+RT and HIIT, in favor of HIIT+RT (+0.23 SMD; 95% CI, 0.03 to 0.42). For the GMMD signature, no significant between-group differences in changes were found between HIIT+RT and UC (+0.08 SMD; 95% CI, -0.18 to 0.34), HIIT and UC (+0.1 SMD; 95% CI, -0.16 to 0.36), or HIIT+RT and HIIT (-0.02 SMD; 95% CI, -0.28 to 0.23). No moderation effects were identified, and no associations were observed between changes in AD brain signatures and cognition or physical fitness. Conclusion: A 12-week HIIT+RT intervention was more effective than HIIT alone in increasing the thickness/volume signature in individuals with CAD, yet no differences were observed compared to UC and the interventions did not affect the GMMD signature. These findings suggest that the intra-session inclusion of RT with HIIT may enhance AD-related brain macrostructure in individuals with CAD more than just HIIT training.