Exercise counters the negative impact of bed rest on executive functions in middle-aged and older adults: A proof-of-concept randomized controlled trial

Objectives: Prolonged bed rest is prevalent among middle-aged and older adults and is associated with multiple negative health outcomes. Therefore, it is important that we better understand the utility of exercise training as a countermeasure to the adverse effects of bed rest. We examined the effect of exercise training on intraindividual variability in cognitive performance among adults aged 55-65 exposed to 14 days of physical inactivity modelled via 6 head-down tilt bed rest.Methods: The study is a non-blinded, parallel-group, proof-of-concept randomized controlled trial. Twenty-three healthy middle-aged and older adults (12 males, 11 females) aged 55-65 were randomized to: (1) 14 days of 6 head-down tilt bed rest (Control) or (2) 14 days of 6 head-down tilt bed rest with daily exercise (Exercise). The National Institutes of Health Toolbox Cognitive Battery assessed executive functions (Flanker incongruent/ congruent and Dimensional Change Card Sort) and processing speed (Pattern Comparison). We assessed cognitive function at baseline, 6 head-down tilt bed rest midpoint, completion, and seven days following completion. We indexed intraindividual variability with two metrics: (1) residual intraindividual standard deviation and (2) intraindividual coefficient of variation. Flanker congruent and incongruent residual intraindividual standard deviations were the primary outcomes. Linear mixed models assessed between-group differences and the moderating effect of biological sex.Results: At bed rest completion, Exercise had significantly lower (better) Flanker incongruent residual intraindividual standard deviation (estimated mean difference = -3.63, 95%CI -6.10;-1.17, p = 0.005) and intraindividual coefficient of variation (estimated mean difference = -0.10, 95%CI -0.19;-0.003, p = 0.022) vs. Control. Sex moderated the effect of exercise on Flanker incongruent intraindividual coefficient of variation. Exercise females had significantly lower intraindividual coefficient of variation vs. Control (estimated mean difference = -0.23; 95%CI -0.34;-0.12, p < 0.001). There were no significant between-group differences in processing speed intraindividual variability and summary scores of executive functions and processing speed (ps > 0.05).Conclusion: Exercise training during bed rest preserved intraindividual variability of executive functions but not processing speed. Trial registration: ClinicalTrials.gov NCT04964999