The U.S. Navy Blue Angels acrobatic team has had problems with G (gravity) forces while performing tight turns during their act. As a result, team members will undergo special training to minimize the effects of tight turns that cause G forces and momentary blackouts. It's a problem that will eventually go away, but not for a while.
The Blue Angels have been putting on acrobatic shows for 62 years now, as a form of public relations for navy aviation. It's dangerous work, more dangerous than combat. Over the history of the team, ten percent of the 262 Blue Angel pilots, have been killed. The last fatality was two years ago, when a pilot pulled a tight turn and momentarily became disoriented because of the G (gravity) forces. Normally, this would not be a problem, because jet fighter pilots were special flying suits, (G Suits) to minimize the G forces.
But the precision flying required of the Blue Angels means that they fly without oxygen masks or G suits. It has to do with the F-18's center mounted joystick. Pilots tend to rest the arm that is holding the stick on their leg or against their body during high G maneuvers, and the inflation and deflation of the G suit could cause them to inadvertently move the stick just enough to cause an accident. In a similar fashion, the oxygen mask hose could get in the way. Pilots don't really need oxygen, since the acrobatic shows are flown at low altitude (below 10,000 feet), so the audience on the ground can see it. Eventually, the F-18 will be replaced with F-35s, which do not use a center (between the pilots legs) joystick.
The U.S. Air Force Thunderbirds use both oxygen and G suits because they are flying the F-16, which has a side mounted stick. Thus there is no problem with G suit air bladders or oxygen mask hoses getting in the way. The F-35 uses two side mounted joy sticks.
For decades now, fighter pilots have had to spend a lot of time building upper body strength in the gym, in order to be able to handle the G forces, even with the G suit. Otherwise, pilots can get groggy, or even pass out in flight, as well as land with strained muscles. All this gym time is one reason fighter pilots are such chick magnets.