Specialized mechanical anchors join up arthropod exoskeletons to muscles and tendon cells. There's a complex network of interconnected matrix constituents, junctions and associated cytoskeletal elements. F-actin based fibres used as tendons fuse onto to myosin based structures which are used for muscle contraction.
The tendons can go through relatively thin areas of the insect with massive leverage. We think about robots and humans as using bones and metal joints with pivots and motors, when arthropods muscles move the exoskeleton rather than interior bones.
The exoskeleton constriction at the abdomen-thorax joint of arachnids and ants demonstrates the relative strength of insect exoskeletons, the exoskeleton material is so light and powerful relative to the size to permit the small form while conserving enough resistance.
The abdomen-thorax joints, which can be multiple segments, are bit it stronger than the legs. They are less likely to get damage there than on their legs. The abdomen and thorax are containers for all the internal organs, which is different than a mechanical limb, so they are bigger.
The slender waist allows for a lot of arthropod behaviour like weaving, stinging, burrowing, preening, symbioses, it's a complex field.
If humans can change the magnet based rotary muscles and use tendon based mechanics they can probably develop very cool machines for the future. here is the human designed comparison for arthropod locomtion: