24: Using Linear Mixed Models to Assess Lactate Response to Exercise in Alzheimer's Disease vs. Controls

Thomas M. Menino Convention & Exhibition Center 

We studied exercise on brain glucose metabolism and lactate availability in individuals with Alzheimer's disease (AD) and controls. Whole-blood lactate was measured at six points during rest and exercise conditions. We modeled lactate response at rest and exercise across two intensity levels (moderate, higher). Linear mixed models were used to assess the relationship, accounting for repeated measures within subjects using random intercepts. We explored the covariance structure of the model and accommodated heterogeneous variances between rest and exercise. Estimated variances varied greatly, from 0.02 at rest to 1.20 after 20 minutes of exercise. Assuming no differences in baseline fitness level, we found a significant difference in lactate between AD and controls in the higher intensity exercise group. When accounting for baseline fitness, this difference is not significant. Our model suggests that those with AD have lower lactate availability under higher intensity exercise than controls. It is unclear if this is due to characteristics of AD or differences in baseline fitness. Future studies should more carefully control for baseline fitness to further explore this relationship.

Linear Mixed Models

Repeated Measures

Heterogeneous Variances

Alzheimer's disease 

Biometrics Section