Final answer:
Muscle atrophy is the wasting or decrease in muscle size due to inactivity, known as atrophy, and can be reversed with exercise, except in the case of sarcopenia in older adults, which is irreversible.
Step-by-step explanation:
The reduction in muscle size due to inactivity is known as atrophy. When muscles are not used, such as during periods of immobilization or inactivity, they begin to weaken and shrink in size, which is a direct impact of the reduction in the number and size of muscle cells and overall protein content. This is commonly observed in humans during prolonged periods of bed rest, or in astronauts who experience zero-gravity conditions in space. Over time, particularly in older adults, a gradual decrease in muscle mass, known as sarcopenia, occurs and is considered a normal part of aging, although it cannot be fully reversed even with exercise.
The effects of muscle atrophy can be profound, ranging from reduced strength and mobility to negative impacts on balance and posture. This weakening of the muscles can lead to further health complications, such as joint issues, due to the lack of support for bones and an increased risk of injuries from falls. While conditions like sarcopenia are a natural part of the aging process, atrophy caused by disuse is often reversible with proper exercise and physical activity, which can help to add structural proteins, increase cellular changes, and maintain or even increase muscle mass.