Compare and contrast internal rotators and external rotators of the shoulder joint

Internal rotation, or medial rotation, occurs when you rotate your upper arms or your thighs toward the midline of your body. For example, if you stand in anatomical position and turn your arms and hands inward, so that your palms face your thighs, you would be internally rotating your shoulder. Several muscles in your shoulder -- namely the pectoralis major, latissimus dorsi and the deltoids -- accomplish this motion. Similarly, if you stand in anatomical position and turn your legs and feet so that your toes point inward, toward the space between your legs, you would be internally rotating your hips. Several muscles in your hips -- the gluteus minimus, gluteus maximus and piriformis -- accomplish this action.

When you externally rotate, or laterally rotate, your shoulder, you turn your arm and hand away from the center of your body so that your palm faces away from your thigh, when you’re standing in anatomical position. For the hip, external rotation involves turning your thigh so that your toes point out to the side. Deep within your hip, underneath your glutes, lie the muscles responsible for external rotation. Your shoulder external rotators include the poster fibers of the deltoids, the teres minor and the infraspinatus

when a reversible reaction is occurring in both directions at the same rate; the products and reactants do not change in concentration. a chemical reaction where the compound is broken into its constituent parts.