I’m a big fan of playing slow to get fast.
I think you occasionally have to ‘burst’ out of your comfort zone so you know how it ‘feels’ at the faster speeds… but consistently playing something too fast, that you arent comfortable with is generally bad.
I’ve noticed that, i’m for sure getting more precise at the lick i am practicing. So in a way i’m getting faster at it. 
Have you ever seen a sprinter jog as his main form of training?
You have you put your body under load to force it to improve, going slow will never put your hands under the added weight/inertia required to build up strength.
Everyone is different, but the worst thing I ever did for my guitar playing was trying to play something fast without being able to play it slow. I honestly wasn’t even aware of how bad I was, until I recorded my playing, and played it back at various speeds, and it was terrible. I was missing many of the notes… it was so sloppy.
Now, I almost always play things slow and precise… and slowly speeding it up after I’ve mastered it. I saw a few youtubers, like Rick Graham mention how important this was. It has helped my playing quite a bit. For the super-tough arpeggios (like the diminished and/or 7th), I often start as slow as 80 bpm (16ths), and very slowly speed up. I’ve found that is the only way I can play them fast.
But as I said before… I still think its a good idea to do ‘bursts’ beyond your comfort zone… so that you can get an idea of how the pattern feels at high speeds. I do these bursts a few times a day for short periods of time.
Also… when I am speaking of playing fast… I don’t mean playing at 280 BPM. I really don’t even touch those speeds anymore. I try to keep things under 200 now.
I’m not advising you play fast before you speed up, it needs to be automatic and clean first by slowly training yourself to perform it correctly, but once you’ve reached that point there is very little to be gained continuing slowly in terms of speed. It’s EXACTLY the same as weight training, you learn the movement, then load up over time, you have to play fast to load up your arms/hands with the weight.
So I agree with you, but think rather than going out of your comfort zone as a concept, it’s better to think of it exactly like weight lifting. There is decades of documented weight training truths and facts out there. As for speeding up on guitar, there’s really not much, troy’s doing a nice job changing that though.
This is interesting. For me when I play slowly my pick hand movements, even the grip and where I hold tension completely changes when I switch to fast mode. So when I’m trying to work through a new motion slowly, I will do a couple runs using my fast grip, then try to maintain that while playing slowly. If you don’t yet have a fast grip, maybe try learning tremolo picking and single string patterns to develop that, then you will know if your string crossing movements will work when sped up.
I think the recent clip of Oz Noy playing scales slowly and the quickly demonstrates that most of us play slowly very differently than when we play quickly.
That’s not to say there’s no place for slow practice, but if you want to get fast, you need to practice playing fast.
I’d say it’s not alyways possible top copy fast motions to slow.
It’s pretty tough to find a good practice routine for that.
Sometimes it even takes more strength to things slower with the same movements as fast, which ist not bad at all cause it helps building strength.
Anyway the worst thing that might happen is that you get the false motions in your muscle memory, so definitely it should be dealt with care.
I personally try to either
a) isolate parts of the fast movement that can be transformed to slower motions
b) practice at the slowest tempo that still feels like the fast (which is mostly still pretty fast) and overemphasize accents
Still that is exactly the process I’d love to get investigated closer.
I’ve noticed this too recently. Around 110bpm 16ths my picking motion start changing somehow, to a hopping motion. I guess i still have to find my second gear.
This is not easy. I have a motion that goes a lot faster, but with this motion i cannot play 2ns patterns.
So my next quest will be the search of a second gear picking motion that works for me.
I’ve been experiment ion this morning. Try taking one of your solid fast riffs, slow it down in small increments. What I’ve found is medium speed is very awkward
I’ve noticed the same. Next thing i am going to try is, starting fast with an excercise, and go slower. Just to see what happens. 
Shawn Lane had the opposite approach: there’s a youtube video “Shawn Lane Talks About Speed” where he tried to “fracture the continuum” after practicing licks slowly for long periods of time by just playing a speed he couldn’t play at all. He found he could play it but it would be sloppy then over time he’d learn to clean it up. This won’t work for everyone (which he admits in the video) and he also admits he had a freakish nervous system. But if you work endlessly on things slowly and aren’t getting anywhere, maybe try that to see if it works for you.
I think that it goes beyond just getting to a certain speed- practicing slow helps with warming up. A few years ago, I attended one of MAB’s clinics where I asked him about practice routines and warming up for gigs - how to get to the optimum level of warming up without playing too much before performance. MAB stated that he had diligently learned and practices his picking at slow speeds over the years to the point where he knows that the max speed picking will ‘be there’ if he warmed up to ‘medium’ speeds before a show.
I think that by practicing slow you are honing your technique - slow enough for your brain to analyse and adapt (creating chunks). You can also play for longer when playing slower, thus working on your stamina a bit like athletes training on sprinting - If you build your stamina to the point where you can go for longer distances at a higher than average speed, you can switch gears and take it to the max!
Thing with mike is his anchoring is very stable, this gives lots of control and minimises a need for readjusting the nervous system. Or warming up.
110 percent …i am going to start practicing standing up from now on !
I think there is a bit of a sweet spot for practicing to play fast . Right around 150 bpm 16ths… It’s a speed that I spend a lot of time at… since it’s fast, but not too fast. You can get the feeling of speed, but be playing slow enough to analyze what you are doing. MAB talks about this mid-range as well.
This video of Martin Miller points to what I have been applying and getting good results with:
Playing to slow to figure out the technique? Absolutely! Playing slow To play fast? Untrue!
Different movements for different situations try to use the same muscles that are involved when one’s running than when walking. You will note that everything will change… in order to improve your pace running, you need to run! Not walk.
As it was said before, sometimes you need to get the feeling of the movement. Speeding up to get the “feeling” of the movement and then working to clean up your guitar playing on high speeds…
Practicing as isolated as possible and in small chunks is by far the best method to get a better technique. I’ve struggled with the Alternate picking motion for years because I’ve never practiced it isolated. I thought, it would develop automatically someday, but it never did. Now I getting an unmeasured amount of evolution in a matter of weeks!!!
It depends upon the person. There have been too many guitarists who have played slowly for most of their practice sessions and become incredibly fast for it to be “untrue.” I had a guitar teacher back in 1989, I believe it was, named Dallas Perkins. He had studied at G.I.T. in Hollywood and was Paul Gilbert’s roommate. Dallas Perkins has a very unique picking style - different from anybody who has been analyzed by Masters Of Mechanics - in that he uses his thumb and fingers to move the pick and is a great alternate picker. He told me he spent about 90% of his practice sessions for technique playing slowly, sometimes extremely slowly, and about 10% of his practice sessions playing fast and it worked extremely well for him.
You can’t compare playing fast vs. playing slow to walking vs running. It’s apples and oranges. It is possible to play slow using the same technique you use playing fast; it’s a choice. I think most people have a tendency to use a complete different motion when they play fast compared to when they play fast and that’s probably where the walking vs. running comparisons started, but you can’t walk by using the same motion you use when you run - it’s not a choice. You can play slow using the same movement types as when you play fast. That is a choice.
The reason it’s bad is that if you play something too fast so that you’re making mistakes and you do it over and over again, you’re literally training your body to play fast and sloppy. You’re picking up bad habits and then by repeating it over and over, you’re ingraining those bad habits into your playing. So then you’re going to have to send a lot of time to unlearn those bad habits. it’s counterproductive.
If I were teaching somebody, and I did used to teach guitar, I’d rather teach a beginner who doesn’t have any bad habits yet than teach an intermediate level guy who has a lot of bad habits. I took a guy who was a beginner back in 1997 - all he knew how to do is strum enough chords to play Wonderwall by Oasis. He knew no scales and no lead guitar. All he had was an acoustic guitar. After two years of taking lessons from me every week, this guy who wasn’t even particularly talented; he wasn’t blessed with a lot of God-given musical talent, was accepted into Berklee in 1999. He was easy to teach because he had no bad habits, he did what I told him to do, and he practiced several hours every day.