Antagonist
Short definition
A muscle on the opposite side of the joint producing torque opposite to the agonist; reciprocally inhibited in healthy coordination.
Full definition
The antagonist lies opposite the agonist across the joint axis and can produce torque in the reverse direction. During the target movement the nervous system down-regulates it (reciprocal inhibition), allowing free motion while residual antagonist activity controls speed and precision. The agonist–antagonist balance is a coordination marker: excess antagonist activity lowers net torque and raises energy cost. In the ExerciseMuscleAnatomy table the antagonist role carries small contributions (5–8%).
Examples
In a biceps curl the antagonist is the triceps, stretching in a controlled manner to damp excess speed.