1. To waste away as a result of the degeneration of body cells: Without adequate exercise, the muscles will atrophy regardless of one's age.

Simon significantly atrophied during his bedridden illness.

Many elderly people have "sarcopenia", when the muscles are atrophying, because either they don't exercise at all or not adequately. People are never too old to exercise!

2. The degeneration, decline, or decrease, because of the lack of using something: Dr. Hughes, the professor, argued that freedom and independence of thought were progressively atrophying because too many people were simply ignoring their political rights.