Issachar is a strong ass couching down between two burdens: Issachar is a strong ass - חמר גרם chamor garem is properly a strong-limbed ass; couching between two burdens - bearing patiently, as most understand it, the fatigues of agriculture, and submitting to exorbitant taxes rather that exert themselves to drive out the old inhabitants.
The two burdens literally mean the two sacks or panniers, one on each side of the animal's body; and couching down between these refers to the well-known propensity of the ass, whenever wearied or overloaded, to lie down even with its burden on its back.