Bad tie rods can sometimes be a cause of stiff steering if the tie rods come loose or the joint in the tie rod end gets hard to move due to wear and tear.
You could also have a bad power steering pump, lack of lubrication or bad wheel alignment that could be causing the stiff steering.
You could also have a bad rack and pinion that is causing the stiff steering.
When a cars steering is working properly it should be very easy to steer the vehicle when the engine is running and the car is going down the road.
If you're getting stiff steering from your vehicle you should get it checked out because it can be caused by a number of different things.