Whoever sets the pace sets the ceiling. Warm up harder than you ask anyone else to.

Groups calibrate to what they observe rather than what they are told, and the fastest reading available is how hard the person in charge is working. Ask for effort you are not visibly giving and the asking gets discounted immediately. Nobody decides this on purpose. They just quietly settle at or below the level they can see.

Do the boring part harder than you have to this week: the warm-up, the setup, the first ten minutes. Say nothing about it. If you want the group at a certain level, that is the level you have to be at while everyone watches you arrive.