Figure 1.

Model of the impact of changes in energy metabolism during healthy and unhealthy aging. (A) Relationship between total daily energy expenditure (TDEE), resting metabolic rate (RMR), circulating creatine phosphokinase (CPK), and fat-free mass (FFM) with frailty index 34 (FI₃₄) in male and female nonagenarians. This panel summarizes this study emphasizing the results for clarity. (B) The model derived from the results postulates that the decrease in maximum energy expenditure (VO₂ max) with age, coupled with an increase in RMR for maintenance and homeodynamics during unhealthy aging, results in a contraction of the energy reserve available for physical activity, compared to what is available during healthy aging. This occurs on the background of the same decrease in TDEE in healthy and unhealthy aging, with a decline in activity energy expenditure (AEE) with age that is exaggerated in the latter.