antagonistic muscles

an·tag·o·nis·tic mus·cles

two or more muscles that produce opposite movements (function), the contraction of one having the potential, in theory, to "neutralize" that of the other; however, in so doing, they are frequently acting as synergists in fixing the moving part.

an·tag·o·nis·tic mus·cles

(an-tag'ŏ-nist'ik mŭs'ĕlz) Those having opposite functions, the action of one tending to oppose or neutralize that of the other.