Is there any upside hypertrophy-wise to take isolation movements not only to concentric failure but isometric and eccentric failure as well? And, if so, is the CNS-cost significantly low to make it worth employing?
For instance, I did rope triceps pushdowns to absolute failure yesterday and spent a minute with an isometric contraction at at the point where I failed concentrically (guessing this says something about my fiber makeup?). Afterwards, my triceps felt as if they had had the work needed to grow, but would it have been better to settle for concentric failure and do another exercise also to concentric failure?
Yes there is a benefit. Adding isometric work once you hit concentric failure promote the release of more growth factors inside the muscle and if you go to eccentric failure after that you impose more muscle damage and mTOR activation.
There is no doubt that this method is a powerful growth stimulus, one that I have used myself from time to time.
And doing it on isolation exercises will indeed be a lot less traumatic than doing it on multi-joints movements. That is not to say that you should do it all the time, or even often. It does take a lot more out of you than a regular set or even a set to failure. How much? we can’t really quantify but certainly at the same level as doing 3 sets to failure (since you hit failure 3 times in one set).
When using that approach I would certainly only use it on isolation exercises, and only on the last set of the exercise. I would also either do it one week out of 4 (week 3 or 4 of a cycle) or as part of a blitz cycle for 2-3 weeks, but then not doing it again for at least 6-8 weeks.
However, I feel like going to isometric failure after reaching concentric failure on isolation exercises is likely a lot let stressful than reaching concentric, then isometric and finally eccentric failure and could be done more often than what I mentioned earlier. However, I’d. still keep it to one set for the exercise.