Each step you take from winking your eyes to running a marathon—occurs due to your muscles. You have more than 600 of them, working day and night to keep you moving, breathing, and even standing up straight. Some muscles you can control (such as lifting your arm), and others work automatically (such as your heartbeat). Ready to put your knowledge of the body's powerhouse system to the test? Time to flex your knowledge!
Wait!
Here're some popular quizzes for you.