The biceps and triceps work together to pull the elbow joint to either a bent or straight position. They form what is known as an agonist - antagonist muscle pair.
The biceps muscle is the muscle in the front of the arm, while the triceps muscle is in the back of the arm. When curling the elbow, the biceps is considered the agonist, or primary muscle. Contracting the biceps muscle bends the elbow, lifting the wrist towards the shoulder. When curling the elbow towards the shoulder, the triceps is considered an antagonist muscle. Contracting the triceps straightens the elbow joint back out in the reverse motion of the biceps contraction.
Like all skeletal muscles, the biceps and triceps are only able to work by contraction, making them two parts of a working pair. Without the triceps, the body would be unable to extend the biceps after contracting, and vice versa.
It is important to strengthen the biceps muscle as well as the triceps muscle to prevent injuries. The biceps and triceps work together to prevent strains and injuries to each other. If the two muscles are not strengthened evenly, they are not be able to compensate and protect the other muscle. When properly strengthened and balanced, the biceps and triceps prevent each other from overextending.