Final answer:
The wasting or decrease in size of a muscle due to inactivity is called atrophy option (a). Atrophy can be caused by diseases, physical inactivity, malnutrition, and is part of the natural aging process known as sarcopenia. Exercise can help mitigate atrophy by strengthening and maintaining muscle tissue.
Step-by-step explanation:
Wasting or decrease in size of a muscle due to inactivity is called atrophy option (a). Muscle atrophy is a condition where there is a reduction in muscle mass due to factors like diseases, such as cancer or AIDS, that cause a wasting syndrome known as cachexia. Age-related decrease in muscle mass, sarcopenia, is also a type of atrophy which shows a gradual loss of muscle strength and function.
Physical inactivity leads to atrophy of skeletal muscle, caused by reduced muscle cell size and protein content. In situations like prolonged bed rest or space flight, humans experience significant muscle weakening and atrophy. Similarly, protein energy malnutrition diseases like marasmus and kwashiorkor result in muscle wasting.
Exercise can delay the effects of sarcopenia by increasing the number of cellular mitochondria, capillary density, and enhancing connective tissue mass and strength. However, sedentary lifestyles exacerbate age-related atrophy, leading to functional impairments and a decline in quality of life.