Straightening the arm after it has been bent requires the:

1. Bending and straightening are opposite movements, so they need the opposite muscle states. 2. Bending the arm contracts the biceps and relaxes the triceps. 3. Straightening therefore reverses that: the triceps contracts and the biceps relaxes. 4. The contracting triceps pulls the forearm back down into line. 5. As an antagonistic pair, they cannot both contract or both relax at once. _Source: NECTA CSEE 2022 Biology 033, Question 1: Multiple Choice Items, item (ix)_