Endurance exercise in aging humans: effects on energy metabolism.

In summary, data suggest that the decline in RMR with advancing age is primarily related to the decline in fat-free mass. However, in addition to the erosion of fat-free mass, other factors such as Na-K pump activity, fat mass, maximal aerobic power, and menopausal status are important determinants influencing the decline in RMR in older individuals. Second, we provide revised prediction equations for RMR that are both gender- and sex-specific and use easily measured variables to facilitate their use in clinical and field settings. Third, preliminary studies suggest that older individuals may have a reduced energy expenditure following meal ingestion, although this is not a universal finding among investigators. Furthermore, several studies suggest that physically active older men exhibit higher thermic responses to a meal than sedentary older men. Data on total energy expenditure in free-living elderly persons are sparse. However, the available data suggest that there is large variation in total energy expenditure in the elderly population, caused primarily by differences in physical activity. The heterogeneity in physical activity makes estimation of individual energy requirements difficult. However, preliminary studies have suggested that measurement of VO2max and other activity indices may be useful markers for estimating energy requirements on an individual basis. Furthermore, attempting to "normalize" total energy expenditure in the elderly by prescribing physical activity is not as straightforward as it seems, due to exercise-induced compensatory reductions in physical activity during the remainder of the day. Levels of insulin-like growth factor-1 decline with advancing age. Preliminary evidence from cross-sectional and exercise intervention studies suggest that the lower serum levels of IGF-1 in older individuals may be partially due to diminished physical activity. Aging is associated with an increase in fasting levels of norepinephrine, primarily influenced by an elevated rate of norepinephrine into circulation; however, the clinical significance of the elevated sympathetic tone is unclear. Endurance training in older individuals has been found to increase basal levels of norepinephrine appearance into circulation, and this has been associated with an increased RMR and enhanced fat oxidation. Optimal exercise interventions need to be identified for the elderly, which maximally increase daily energy expenditure and offset metabolic deterioration with advancing age.