I’m unsure of what exactly I get out of this, but it definitely does something good.
It may just be a matter of it flushing the muscle with blood, each second of contraction being equivalent to a rep making this a great work capacity/volume tool, and when held for long enough times a good mental toughness exercise.
I start the stack at 70lbs which is honestly too light for 5-10 reps.
Then jump 30-40lbs for sets of 5 until the stack is reached (260lbs) where I either do holds of 30+ seconds or a rep out (generally 20-30 reps) then holds.
I dont like doing lots of leg extensions, but this protocol I do like.
The protocol is a nice little way to get the leg work you need done by in and out 5-10 minute style.
-J