Final answer:
Muscles undergo atrophy when they become weaker and decrease in size due to inactivity, which can often be reversed with exercise, except when it is age-related, a condition known as sarcopenia.
Step-by-step explanation:
When your muscles become weaker and decrease in size and strength due to the lack of use over a period of time, they begin to atrophy. This reduction in muscle mass due to inactivity or immobilization can often be reversed with exercise. However, muscle atrophy with age, referred to as sarcopenia, is irreversible. As people age, the natural decline in muscle mass leads to a loss of strength which is required for posture, mobility, and overall physical functionality.
Muscle hypertrophy and atrophy are two opposing conditions affecting muscles. While exercise can lead to hypertrophy, increasing the size and strength of muscles, inactivity or conditions like aging, disease, or extended periods of immobilization result in atrophy. For example, astronauts experience muscle atrophy due to weightlessness in space, and individuals with prolonged bed rest or suffering from diseases like cancer or AIDS also exhibit noticeable muscle wasting.
While sarcopenia with age cannot be completely prevented, maintaining an active lifestyle with regular exercise can delay its effects by increasing the number of cellular mitochondria, enhancing capillary density, and strengthening connective tissue. The ability to mitigate the effects of atrophy underscores the importance of physical activity in preserving muscle mass and function as we age.