The biceps' antagonist muscle group is the triceps. The triceps work opposite to the biceps during the curling motion, controlling the extensionof the arm as the biceps contract. This antagonistic relationship between the biceps and triceps helps to stabilize the elbow joint during the curling motion and allows for smooth and controlled movement. Strengthening both the biceps and triceps isof the arm. When the biceps contracts to bring the weight towards the body, the triceps lengthen to control the movement. Similarly, when the weight is lowered back down, the triceps contract to bring the arm to its original position while the biceps lengthen. This balance of contraction and relaxation between the two muscles is what allows for smooth and controlled movement of the arm during the bicep curl exercise.