Final answer:
The trapezius and rhomboid muscles (major and minor) are active to support the shoulder girdle during a standing posture, as they position the pectoral girdle on the posterior thorax.
Step-by-step explanation:
The muscles active to support the shoulder girdle during a standing posture include the trapezius, rhomboid major, and rhomboid minor.
These muscles are part of a group that positions the pectoral girdle, located on the posterior thorax.
The trapezius stabilizes and moves the scapula in multiple directions, while the rhomboids contract to move the scapula medially, which can pull the shoulder and upper limb posteriorly, providing stable support for the shoulder girdle.