Physical Activity Level Measured By Doubly Labelled Water Method Is Associated With Brain Volume And Cognitive Function, But Not With Muscle Size In The Older Adults.

It has been established that physical activity, or regular habitual exercise, has beneficial effects on the brain and muscle function. Doubly labelled water (DLW) method is the gold standard to assess physical activity level (PAL) accurately without constraints and restrictions. However, it has not been explored whether physical activity level, assessed by DLW method, is associated with brain volume, cognitive function, and thigh muscle cross sectional area (CSA) in the older adults. PURPOSE: To determine the association between PAL, assessed by DLW method, and brain volume, cognitive function, and thigh muscle CSA. METHODS: Fifty-three participants participated the experiment (41 females, age: 71.7 ± 6.9 yr., height: 153.9 ± 8.3 cm, weight: 54.0 ± 11.4 kg). PAL was calculated as total energy expenditure divided by the basal metabolic rate. Structural images of the brain were measured using magnetic resonance imaging (MRI). Cognitive function was assessed using the Trail Making Test. Quadriceps muscle CSA was measured at the mid-thigh (50% of the femur) regions using MRI. Total grey matter and hippocampus volumes or muscle CSA were normalized using total intracranial volume or lean body mass. We performed a correlation analysis to determine the association among variables. RESULTS: PAL was correlated with the total grey matter (r = 0.547, p < 0.001) and hippocampus (r = 0.499, p < 0.001) volumes, and also with TMT-A (time, r = -0.268, p = 0.046) and TMT-B (number in 60 seconds, r = 0.332, p = 0.013) performances. Conversely, PAL was not correlated with the quadriceps muscle CSA (r = 0.158, p = 0.267). Muscle CSA was not associated with the total grey matter (r = 0.181, p = 0.204) and hippocampus (r = 0.124, p = 0.387) volumes. CONCLUSION: DLW-measured PAL was associated with grey matter/hippocampus volumes and cognitive function, but not with the thigh muscle CSA.