How physically demanding is driving a formula 1 car?

With no Power Steering and accelerations of up to 6gs, driving an F1 car is a huge physical feat. In addition the cars are so reliant on downforce, going slowly means that they lose most of their grip and the sheer power-weight ratio means the slightest mistake will send the car into a spin. F1 drivers - even the ones dragging a car round to come in last are hugely talented.