Why is proper equalization critical during descent and ascent?

Proper equalization is critical during descent and ascent primarily to prevent ear barotrauma due to pressure differences. As divers descend, the surrounding water pressure increases, which can create a pressure imbalance in the air spaces of the body, particularly the ears and sinuses. If the pressures are not equalized by methods such as the Valsalva maneuver or Toynbee maneuver, it can lead to pain, discomfort, and potential injury known as barotrauma.

Equalization allows divers to safely manage the change in pressure by equalizing the pressure in the middle ear with the external water pressure. This is crucial because if the pressure in the ear is not equalized, it can lead to issues such as ruptured eardrums or other serious injuries, making the dive unsafe. During ascent, it is equally essential to maintain proper equalization to manage the decreasing pressure effectively and avoid complications associated with decompression.

Other options relate to aspects of diving but do not address the critical importance of equalization with respect to pressure changes in the body and the risk of barotrauma. While swimming efficiency, fatigue, and buoyancy are important factors in diving, they are not directly linked to the necessity of equalizing pressure during a dive.