Think of insulin resistance with a lock and key analogy. In your body, glucose in the blood is trying to get through the door to your muscle and fat cells. To get inside the cells, the glucose must have a key to open the door. Insulin is the key that goes into the lock (or insulin receptors, in this case) to make it open. If you have the key (insulin), but the keyhole on the lock is blocked or the key won't turn when it goes in, then glucose can't enter, and you have insulin resistance — lots of insulin available but not working well. When the keys and the keyholes are functioning well together, the doors open, and glucose enters the cells and lowers the levels in the blood.