Looks like you are looking for the antagonistic pair. The muscular group that flexes the arm would be the antagonistic pair of tricep brachi and the brachialis.
your tricep flexes at the elbow when you straighten your arm
The brachialis is a muscle in the upper arm that flexes the elbow joint.
biceps & triceps?
pectoralis
The biceps muscle is made of skeletal muscle, and it flexes your arm.
This is known as the bicep. The muscle that extends the lower arm is known as the tricep.
biceps brachi
Biceps brachi..alone or in combination with brachialis muscle flexes the arm, elbow and fore arm
Palmaris Longus
It flexes the arm at the elbow.
latissimus dorsi
The biceps muscle flexes and the triceps extends.