Final answer:
The swing limb has key goals such as enabling mobility for species that move by swinging from branch to branch, with the limbs undergoing cycles of flexion and extension. In humans, the upper limbs are highly mobile for various activities, whereas the lower limbs provide support and stability for locomotion.
Step-by-step explanation:
The key goals for the swing limb revolve primarily around mobility and balance, particularly in species that have developed the ability to move by swinging their arms from one branch to another, such as tarsiers with their expanded finger-like parts for improved grasping. This limb movement is characterized by a cycle of flexion and extension, where flexion decreases the angle between the bones and extension increases it, facilitating the swing motion utilized in arboreal locomotion.
In humans, because of our upright stance, different functional demands are placed on the limbs. The upper limbs are highly mobile and are used for a wide variety of activities, thanks to the large range of movements made possible by the pectoral girdle and our ability to manipulate objects with our hands and opposable thumbs. The lower limbs, in contrast, are adapted for weight-bearing support and stability in locomotion via walking or running. Identifying these limb movements and their functions is part of understanding the dynamics and mechanisms of bodily motion.