Which of the following is NOT one of the three functions of human muscles?

The option indicating the function of protecting bones is not considered one of the primary functions of human muscles. Human muscles primarily serve three essential roles: enabling movement of the skeleton, facilitating the movement of organs (such as the heart and digestive tract), and pumping blood through the cardiovascular system, particularly the heart's muscle tissue.

Muscles contract and relax to produce voluntary movements, allowing for activities like walking, running, and grasping. Additionally, certain muscles work involuntarily to move substances within organs, aiding in essential bodily functions. While muscles contribute indirectly to the protection of bones by providing support and maintaining a healthy musculoskeletal system, they do not have a direct function of safeguarding bones themselves. This distinction is important for understanding the roles that muscles play in the body compared to other elements of the skeletal system.