RainBox shows how you can quickly create a rubber limb with DUIK.
Rigging characters with After Effects is really a mixed bag. Thre are what seems to be a wave of third-party tools out there that offer an easy way to rig limbs. Tools like Rubber hose let you easily create a classic rubber limb that has the attributes of typical cartoon characters. You can also generate rubber arms and such using the free DUIK tools too.
Check out this short quick tip tutorial from Rainbox that shows how easy it is to create a rubber limb using DUIK. The best part is that all the simple techniques covered are easily adaptable to more complex rigs and characters. Fun!