Which physiological function is known to decline with normal aging?

Maximal aerobic capacity, also known as VO2 max, is recognized for its decline with normal aging. As individuals get older, several physiological changes occur that contribute to this decrease. These can include a reduction in cardiac output, decreased muscle mass, and a diminished ability of muscles to utilize oxygen efficiently. This decline affects overall endurance and performance in physical activities, which is particularly significant for older adults as it impacts their ability to maintain an active and independent lifestyle.

In contrast, resting heart rate typically remains stable or may even decrease slightly as a person ages, and plasma volume does not show a consistent decline with aging. Hematocrit levels, which refer to the proportion of blood volume occupied by red blood cells, also generally stay within a normal range unless affected by specific health conditions. Thus, maximal aerobic capacity stands out as the most directly impacted physiological function by the aging process.