If the spoilers are deflected and steady level flight at a constant speed and load factor is to be achieved the following will apply.

Spoilers are designed to increase drag and reduce lift. If this is the case when they are extended the speed will drop off unless thrust is increased to balance the drag and lift would further decrease. The reduction in lift can be recovered by increasing the angle of attack which further increases the drag and requires even more thrust. Drag thus increases whilst lift remains constant.