Triceps contraction extends the elbow joint

Steps:

• Identify triceps brachii as the main extensor muscle, originating on the humerus and inserting on the ulna.
• Note that contraction shortens the muscle, pulling the ulna proximally toward the humerus.
• Recognize this force extends the forearm, moving bones like the radius upward relative to the elbow.
• Confirm the primary action straightens the arm without flexing or raising the upper arm.

Why A is correct:

• Triceps contraction pulls the forearm bones, including the radius, upward to extend the elbow, as defined by its role in antagonistic muscle action at the hinge joint.

Why the others are wrong:

• B: Biceps relaxation is a secondary antagonistic response, not a direct result of triceps contraction.
• C: Elbow bending (flexion) occurs with biceps contraction, opposing triceps action.
• D: Upper arm raising involves shoulder muscles like deltoids, not elbow extensors.

Final answer: A