and you think we haven't had extensive training in the gates? i trained with them in grimm for a month before mastering them idk about ds mugi and ali but i can vouch for myself that i have trained just as much as them :| just sayin to thatGai and Lee are the Main user of Gates they've extensively trained thats why they are almost near resistant to the effects.
Ali is using his Gai bio but Gai can only use up to the 6th Gate. by forcibly using the 7th Gate. Gai's Body cant with stand the pressure of using the 7th Gate and therefore suffers the consequences. the effects are immediate the gates just dont allow the user to realize that. as it completely numbs out pain after the third or 4th Gate i think.
So people such as you who use gates but dont have a Rock Lee or Gai bio feel the effects soon after. you deactivate them. it doesnt matter how long you use them your body still is effected as it surpasses the brains limits placed on the body. which keep humans from ripping themselves apart with there own strength. opening the gates breaks that limit. and therefore you rip your self to shreads as you move, attack, or just sit there. as its even affecting your nervous system.
and if he is using a gai bio how can he use ninjutsu