The Valsalva maneuver (forceful attempt to exhale against a closed airway) has been the subject of debate in the fitness community.

On one hand, it would be somewhat unavoidable when lifting heavy weights (you may have seen heavy lifters turning red while lifting heavy weights as they close their mouth forcefully while tryinValsalva maneuverg to exhale). Not only this is a common practice in gyms and falls into the category of natural instinct when lifting heavy loads, it is in fact a significant part in some martial arts. Different martial arts philosophies consider the Valsalva maneuver an essential ingredient in order to increase intra abdominal pressure. An increased intra abdominal pressure is a like a bubble of air that stabilizes the lower back, and profoundly raises strength and balance while increasing the safety of the subject when preforming heavy lifting.

It is also being used as a medical tool, for example in clinical diagnosis of problems or injury in the nerves of the cervical spine.

On the other hand, the Valsalva Maneuver  has been considered many times by western fitness philosophies as a dangerous act that can spike blood pressure to the roof. There are a few negatives to this maneuver that cannot and should not be ignored:

In the last few decades, western fitness philosophies has been teaching how exhale and inhale while preforming exercises in order to try and avoid the maneuver while eastern fitness philosophies have taught how to take advantage of the intra-abdominal pressure in order to exert more force and power whilst increasing the stability of the lower back.

A new review set some interesting recommendations while looking at the latest advances in research. The review suggests a brief Valsalva maneuver (i.e. around 3 seconds) to coaches and athletes who wish to improve strength and conditioning. The recommendation applies to those who do not suffer from:  cerebrovascular disease, cardiovascular disease and hernias.

You can read the full paper here