Which muscle is responsible for straightening and twisting the arm?

The triceps muscle is responsible for straightening the arm, a motion known as extension. When the triceps contracts, it pulls on the elbow joint to straighten the arm from a bent position. This muscle is located at the back of the upper arm and plays a crucial role in pushing movements, such as when you push your body up from a seated position or perform a push-up.

In addition to its primary function of extending the arm at the elbow, the triceps can also assist with rotational movements of the arm, especially when combined with shoulder action. While it is not the primary muscle responsible for twisting the arm, its role in arm extension allows for better mechanics during such movements.

In contrast, the biceps mainly facilitate flexion of the arm at the elbow and assist with twisting the forearm, but they do not contribute to straightening. The deltoids are mainly involved in shoulder movements and do not primarily perform actions directly at the elbow. The forearm muscles do assist with wrist and hand movements, but they do not play a direct role in the activity of straightening and twisting the arm in conjunction with the elbow joint. Thus, the triceps is the muscle specifically involved in straightening the arm.