metabolic stress is always good, allows for better nutrition partitioning, more pumped look, longer glycogen replenishing time, so logically it would be a good idea to increase the frequency of metabolic stress, but the problem is that most metabolic fatiguing exercises are a strain on the CNS(greater freq + higher reps = fatigue on the CNS). So, the best way to fiddle with this is to find the greatest freq of metabolic stress junk you can do while still being able to complete the alloted number of sets/reps for your heavy set.
i can handle 1 set of 15s pulsed at peak contraction 2x a day during my 5s and post 5s. metabolic stress is pretty high during the 10s and 15s so they aren't really needed that much.
how much you need to do is up to you, the more you do the better as long as you can still keep consistent volume and consistent incrementing.
pzhang