Final answer:
Muscles can only contract, not push, which is why virtually all muscles in the body exist as antagonistic pairs such as the biceps and triceps. These muscle pairs include flexors and extensors, which enable various necessary movements of the skeletal system.
Step-by-step explanation:
It is true that muscles can only pull, or contract, and not push. Therefore, they exist mostly in antagonistic pairs to provide the necessary movement and stability to the body's skeletal system. One familiar example of such a pair is the biceps and triceps in the upper arm. The biceps is a flexor which contracts to bend the arm at the elbow, while the triceps is an extensor, contracting to straighten the arm. Other examples of opposing muscle pairs include those that control the movements of the legs, feet, and hands, as well as those responsible for facial expressions and several other body movements.
Antagonistic Muscle Pairs
Muscles like the biceps and triceps demonstrate the concept of agonist and antagonist muscles. An agonist muscle causes a particular movement, while the antagonist muscle moves in the opposite way to slow or stop the movement. This functional arrangement allows for precise control of movement and maintains posture and joint stability.
Skeletal muscles often come in such pairs to permit a wider range of controlled movements. For example, the muscles responsible for forearm rotation, the pronator teres, and supinator also work as antagonistic pairs.