Board Thread:General Discussion/@comment-12301089-20131211070550/@comment-24282510-20140425020245

Blazenite104 wrote: I just mean that we don't really know why it specifically takes that long. communication and cooperation with the blade is apparently key, beyond that we really don't know exactly why it takes that long.

Probably something due to the sudden shift in power to a much higher power level. That can't be easy on ones muscles (heart specifically) and resistu ports. Remember back when Ichigo fought Byakuya in bankai and HIchigo appeared and said something along the lines of his bankai was crushing him. And then theres the issue of being able to put out that much power for a good period of time. Which i think was touched up on during Byakuya and Renji's fight.

So this leads me to think it is a sustainable issue similar to long range endurance running. One can hold bankai but it damages them also.