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How do flexible joints allow arthropods to move despite having hard exoskeletons?

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A spiny lobster (Palinurus elephas) with long, striped antennae and spiny body stands on sandy ground near a rocky crevice underwater. — arthropod Spiny lobster, or rock lobster (*Palinurus elephas*).

Arthropods overcome the limitations of their rigid exoskeleton by utilizing a specialized system of joints that allow for movement while maintaining structural integrity.12

The exoskeleton is divided into distinct plates over the body and cylinders around the appendages. At the junctions between these segments, the cuticle is thin, flexible, and folded. Because this jointed area lacks the rigid exocuticle, it can bend, with the folds providing the necessary surface area to accommodate the movement.1

The mechanics of this movement involve:
* Lever Systems: Muscles attach to the inside of the skeleton, often via apodemes (chitinous rods), allowing the exoskeleton and muscles to function together as a lever system.13
* Antagonistic Muscles: In many joints, pairs of antagonistic muscles span the segments to move them in opposite directions.43
* Hydrostatic Pressure: In some leg joints, where extensor muscles are absent, straightening is achieved through the hydrostatic pressure of the hemocoele and the action of proximal depressor muscles.4

This design allows arthropods to achieve significant mobility, ranging from rapid running and jumping to complex burrowing, while the rigid plates provide essential protection and support.41