both the 2 min ab ciruit and the 6 min ab circuit include isometric holds
stomach vacuums i hold for as long as i can (about 5 sec til i start to run outta breath) and i include them on my two rep based core days (wed and sat)
i really only do plyos once or so a week, but once i hit fall they will become a bigger part of my program as my lifting volume begins to lighten. i want to be used to a good volume of plyos by winter so i can use them as replacement speed work since facilities in the NE in the winter are limited