Your muscles can become very weak and when you become older there's a 1/4 chance you can lose your muscles.
Muscles are for more than lifting. They keep us walking, jogging, swimming, or dancing. They burn off excess calories, and they make us look fit, not flabby.
Our bodies can make 11 of the 20 amino acids that are the building blocks of protein, and therefore of muscle tissue.
When you reach your late 30s or 40s most people start lose a quarter pound of their muscles a year so that's why you wanna keep being active so you can be in good shape.
Schardt, D. (2011). STAYING STRONG: How exercise & diet can help preserve your muscles. (cover story). Nutrition Action Health Letter, 38(3), 1.