Here’s what Tim Patterson said about it in issue #121 of T-mag (see how handy the search engine is!) :
"I’m very familiar with SuperSlow training. I find it an excellent protocol to use for the general population and for rehab, mostly for increasing strength. But regarding building mass, it’s the absolute worst type of training I’ve ever encountered.
Now, when I say I’m very familiar, I don’t mean I’ve just tinkered around with SuperSlow. It’s quite the opposite. Over the last 15 years, I must have had personal contact with at least 200 SuperSlow trainees. And without exception, every one that trained hard with the protocol for an extended time ended up stronger, but they were also fatter and smaller!
It’s no joke. These guys just keep adding exercise resistance while shrinking and smoothing out. It’s a dreadful experience to watch someone go through, too. They have to play a lot of mind games with themselves (mental masturbation) to keep motivated to train. And they often become “religious” fanatics for SuperSlow, driving people around them crazy. Go figure.
The reason you can’t build mass with SuperSlow is that there isn’t enough repetitive neurological stimulation to the muscle cell to elicit hypertrophy. To gain muscle, you have to recruit more motor units, repetitively. SuperSlow is too gentle on the muscle fibers, uses way too few repetitions, is performed much too infrequently to work — and to top it all off, it’s painful torture to go through.
And in the real world, it doesn’t work!
My recommendation is to run, not walk, away from SuperSlow training. And if you must, only perform one set of this slow-mo stuff, rarely."