The role of age and physical fitness on the relationship between physical activity and executive function.

OBJECTIVE: Few studies examine the relationship between physical activity, multiple physical fitness domains (cardiorespiratory fitness, strength, speed), and cognition. Our objective was to investigate the association between physical activity and executive function in middle-aged and older adults and examine whether modifiable physical fitness components explain the relationship between physical activity and cognition. METHOD: Self-reported moderate-to-vigorous physical activity and objective measures of cardiorespiratory fitness (2-minute walk test), strength (grip strength), speed (4-meter walk test), and executive function were collected from 623 adults within the Human Connectome Project-Aging (ages 36 - 100 years; mean = 59.2 years; 57.8% female). Relative importance metrics, multiple regression, and conditional process analysis were used to examine relationships of age, physical activity, and physical fitness with executive function. RESULTS: Greater physical fitness was related to better executive function performance (β = 0.28, p < .001). Physical activity was not associated with executive function (β = -0.04, p = .16). There was an indirect relationship between physical activity and executive function through physical fitness (ab = 0.02, 95% CI: 0.004 - 0.04). This association was explained primarily by the indirect association of cardiorespiratory fitness with physical activity and executive function. The indirect association of cardiorespiratory fitness with physical activity and executive function was significant in older study participants (mean (59 years) and + 1 SD (74 years)), but not younger (-1 SD (44 years)), although between-group comparisons were not significant. CONCLUSIONS: These data highlight potential differential associations with cognition when considering physical activity and physical fitness, and the importance of considering multiple domains of physical fitness in relation to physical activity and cognitive performance.