The shoulder takes the majority of the stress induced by the muscle wire. It also holds the spring that returns the legs to their contracted positions and the sensors that tell the legs' positions at any given time. In addition, the shoulders support the brain and the eyes. The pins on the insides of the shoulders are part of the locking mechanism that holds Octofungi together without any screws or metal fasteners.

The shoulders are designed to accommodate 160 newtons of force between the muscle wire anchor points and the pulley. They also accommodate the same force between the spring and the leg anchoring point. This force is equivalent to a 17 kg (37 pound) weight. The legs' design shows a meld of strength maximization, weight minimization, and overall aesthetics.