Objective
Age-related declines in physical activity are commonly observed in human and animal populations, but their physiological bases are not fully understood. We hypothesize that a lack of available energy contributes to low levels of activity in older persons.
Design
Cross-sectional analyses of relationships between physical activity level and energy availability were performed in 602 community-dwelling volunteers aged 45 to 91 yrs from the Baltimore Longitudinal Study of Aging (BLSA). Energy expenditure was measured at rest and during a maximal 400-meter walk for calculation of “available energy.” Overall and vigorous physical activity levels were assessed using standardized questionnaires. General linear regression models were used to assess the relationships between available energy and general and vigorous physical activity, and stratified analyses were used to analyze the possible differential association between available energy and physical activity across high and low (peak sustained walking VO2 <18.3 ml O2/kg/min) levels of aerobic fitness.
Results
Low available energy was associated with low levels of total physical activity (β = 64.678, p = .015) and vigorous activity (β = 9.123, p < .0001). The direct relationship between available energy and physical activity was particularly strong in persons categorized as having low aerobic fitness between available energy and physical activity with both total (β = 119.783, p = .022) and vigorous activity (β = 10.246, p = .015) and was independent of body composition and age.
Conclusions
Findings from this study support the hypothesis that available energy promotes the maintenance of physical activity in older persons. The findings also run counter to the perception that age-related declines in physical activity are primarily societally or behaviorally driven.