Which of the following is true about internal forces?

Internal forces refer to the forces that arise from within a body or system. This includes forces generated by muscles, ligaments, and the skeletal structure during movement or while at rest. The key characteristic of internal forces is that they are the result of interactions between various components of the body itself.

Since internal forces originate from within the body, they play a critical role in stabilizing and controlling movements. For example, when performing an activity such as running, internal forces generated by muscle contractions help to maintain posture, support joint movements, and provide the necessary energy to propel the body forward.

This understanding of internal forces is vital in biomechanics, as it allows for a better grasp of how the body manages load and movement. Recognizing their origin helps differentiate them from external forces, which act on the body from the outside environment like gravity or ground reaction forces. Hence, the assertion that they originate within the body is accurate and foundational to the study of biomechanics.