Final answer:
Muscle atrophy is the reduction in muscle mass and strength due to factors like disuse. When muscles are not regularly exercised, they can become weaker and lose mass, leading to functional impairments.
Step-by-step explanation:
Muscle atrophy is the reduction in muscle mass and strength due to various factors. Disuse is one of the causes of muscle atrophy. When muscles are not used or exercised regularly, they can become weaker and lose mass. This can result in functional impairments and reduced quality of life.