A "muscle round" is where you use a weight you could normally do about 12 reps with, but only do 4 reps with it. You rest 10 seconds and do another 4 reps. Do this 6 times. Then, on the last mini-set, you do as many reps as possible (AMRAP):
Do these on the vertical side of a preacher bench. (If you use the angled preacher bench, there's virtually no resistance at the top of the movement.)
This gives you a built-in work to rest ratio because you'll be swapping hands on each mini-set. The right arm does 4 reps, the left arm does 4 reps; back and forth like this for the entirety of the round.
Do 2 complete muscle rounds to light the brachialis up, taking 2-3 minutes between each round.