The muscles of the heart get weak with a decrease in physical activity.
Мушакҳо дар синни 14-17-солагӣ босуръат инкишоф ёфта, дар синни 18-солагӣ баробари мушакҳои калонсолон мешаванд.
Muscles develop quickly from the ages of 14 to 17, and at the age of 18 are the same as adult muscles.
мушак can also mean “little mouse” and “missile”.
You can learn more human body words at Decks (formerly Memrise) here: Tajik Human Body. The site is free to use, but you have to sign in.