What muscle are worked if I lower my arm? It can't be the deltoid, as front and lateral raise use deltiod. But lets say I am upside down and lower my arm, which muscle I will work out? Just like triceps are opposite to bicep, what is opposite to deltoid?
The topic you talk about is Synergist(something such as a chemical or a muscle that enhances the effectiveness of an active agent) and Antagonist(a muscle that contracts with and limits the action of an agonist with which it is paired) muscles. The action of deltoid is shoulder abduction, flexion and extension so synergists of deltoid are Supraspinatus, Infraspinatus, Teres major and minor, Subscapularis and antagonists of deltoid are Pectoralis major and minor, Subclavius, Serratus anterior, Trapezius, Latissimus dorsi, Rhomboid major and minor, and Levator scapulae.