Question

How do muscles in the arm work in pairs to bend and straighten
it?

Answer 1

Answer:

When one muscle in a pair contracts, to bend a joint for example, its counterpart then contracts and pulls in the opposite direction to straighten the joint out again. ... To do this, your triceps muscle, on the underside of your upper arm, contracts and straightens your arm out.

Answer 2

Answer:

Answer is given in Explanation

Explanation:

When one muscle in a pair contracts, to bend a joint for example, its counterpart then contracts and pulls in the opposite direction to straighten the joint out again.

When your biceps muscle in your upper arm contracts, it pulls your lower arm in towards your shoulder. However, when it relaxes, your biceps cannot push your arm back out. To do this, your triceps muscle, on the underside of your upper arm, contracts and straightens your arm out. 

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