The video clip of Rain's 9G pressure training is becoming a hot topic online. To prepare for production, the cast of R2B: Return to Base all underwent endurance tests to prevent symptoms that may be experienced from too much acceleration force in high-speed jets, including loss of consciousness and change in vision. The test measures G-force, which is a unit used to measure the force that a human body is subjected to when accelerated. A typical person can withstand about 5G before losing consciousness.
Wearing a G-suit, Rain shocked his costars and military trainers alike when he challenged himself with the pressure tests. Said his costar Kim Sung-soo, "Once you past the 6G test, you're ready to board a jet. Rain was the first one out of all of us to pass the 6G test". He continued, "You're pretty much set once you pass the 6G test. But Rain insisted that he do the 9G pressure test as well. He passed. Passing a 9G test is something that only the top 1% of jet pilots can do, and you certainly don't do a 6G and 9G test all in one day. The air force said that this is the first time anyone has done that".
Rain's costar, Yoo Joon-sang, succeeded in the 6G test after fainting during the first 2 tries. In order to get into character and into shape for the shooting of R2B: Return to Base, the entire cast underwent training periods that lasted from 4 months to 1 year.