Which effect is caused by -Gz acceleration?

The correct choice relates to the physiological responses experienced during -Gz acceleration, specifically leading to extreme headache and congestion in the head. Under negative Gz acceleration, the force acts in the opposite direction of gravity. This can cause blood to be displaced from the upper body towards the lower extremities, leading to congestion and increased pressure in the head. As blood pools away from the brain, individuals may experience symptoms such as headaches and a feeling of pressure or fullness in the head.

Understanding the effects of G-forces on the body is crucial in aerospace physiology, especially for pilots and aircrew. The head and upper body are particularly sensitive to shifts in blood flow during such accelerations, and managing these effects is key to maintaining performance and preventing injury or loss of consciousness.

The other effects listed, while potentially associated with other types of accelerative forces or conditions, are not the primary symptoms associated with negative Gz acceleration. This distinction is important, as it highlights how the body reacts specifically to the accelerative forces acting in a downward direction relative to the vertical axis.