One muscle is for "pushing" against a force, and the opposite part of the pair of muscles "pulls". If you push someone in front of you away from you, you're using your triceps. If you pull someone closer to you, the bicep works.
Muscles work in pairs because they can only contract and need an opposite force to enable movement. The biceps and triceps are good examples of this, as the biceps flexes the arm while the triceps extends it, allowing for coordinated movement. This antagonistic pairing is essential for smooth and controlled limb actions.
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