I know that there have been studies that show that more rest between sets, given the same volume, leads to significantly more gains, at the expense of more time in the gym, so circuit training would seem like the logical thing to explore.
By circuit training, I mean doing exercises in the order of
A B C D A B C D A B C D
A A A B B B C C C D D D
Two variants of the question:
Is circuit training superior (for hypertrophy / strength / muscle endurance) given
(a) the same time in the gym and the same volume (so the same rest between sets)
(b) the same volume, but less time?
Have there been studies done on this?