I know how tempting it is to rush through your sets in an attempt to pack as much volume as possible into a short period of time. This week, however, you have to slow down, hit Pause at some point during each rep, and let the isometric training do its thing. Fend off that weight while you're in the paused position, making sure those target muscles are contracted as tightly as possible.
It can feel scary to pause and hold during a move like a skullcrusher, when you have weight just hanging out right above your head, but that's why it's important to be smart about the weight you choose to use. We're working time under tension this week, which is much more important than the sheer amount of weight you use.
If you're not sure how to perform a paused repetition on one of the lifts, be sure to watch the Week 4 video for form tips and coaching cues.