How does aging affect the reserve capacity of the human heart, lungs, kidneys, and brain?

Aging is characterized by a progressive decline in the physiological functions and reserve capacities of major organs, which reduces the body's ability to adapt to metabolic and environmental stress. This decline is often linked to a loss of cells and reduced cellular efficiency, such as decreased enzyme activity.1

• Heart: While resting heart rate remains stable, the heart's reserve capacity diminishes with age. Structural changes, including the loss of muscle fibers and reduced power of contraction, lead to a significant decrease in the amount of blood pumped over time. Consequently, the heart takes longer to recover from physical stress.23
• Lungs: Aging reduces vital capacity and lung elasticity due to changes in collagen and elastin. While oxygen transfer is generally sufficient at rest, the reserve capacity to move oxygen during strenuous exercise is impaired.43
• Kidneys: The kidney’s ability to concentrate urine declines, requiring more water to excrete waste. This is largely due to a loss of nephrons and reduced blood flow, though the body often compensates for this reduced capacity under normal conditions.5
• Brain: Aging is associated with slower processing speeds and impairments in short-term and secondary memory. However, cognitive decline is not inevitable; factors like aerobic exercise and continued learning can help maintain mental alertness and cognitive performance.67