Which muscle on the back of the upper arm extends the elbow?

Which muscle on the back of the upper arm extends the elbow?

• A. Triceps brachii
• B. Biceps brachii
• C. Deltoid
• D. Humerus

Answer: (A)

Elbow extension is performed by a muscle on the back of the upper arm that straightens the forearm. The triceps brachii contracts to pull on the ulna, straightening the elbow joint. This muscle has three heads and plays the main role in straightening the arm, especially when pushing or reaching. The other options don’t fit this action because the biceps brachii is on the front of the arm and flexes the elbow, not extend it. The deltoid is a shoulder muscle that mostly moves the arm at the shoulder, not the elbow. The humerus is a bone, not a muscle.

Elbow extension is performed by a muscle on the back of the upper arm that straightens the forearm. The triceps brachii contracts to pull on the ulna, straightening the elbow joint. This muscle has three heads and plays the main role in straightening the arm, especially when pushing or reaching.

The other options don’t fit this action because the biceps brachii is on the front of the arm and flexes the elbow, not extend it. The deltoid is a shoulder muscle that mostly moves the arm at the shoulder, not the elbow. The humerus is a bone, not a muscle.