Because I am always emphasizing "relaxation", and the need for the most careful approach in practicing guitar, students will sometimes get really paranoid about practicing. Especially after learning from me that they are suffering from chronic body tension due to years of rushed and tense movements!
They get the idea that I am telling them that ANY body sensation is bad, as though they are looking for some state of complete numbness while playing guitar, thinking that is what I am recommending. I am not. I am talking about achieving, in any playing situation, a state of minimal and balanced effort through awareness and control.
Paradoxically, on the way to achieving this state of ease in playing, we sometimes must deal with quite a bit of effort and discomfort in practice. The secret is in knowing how to respond to the feelings of effort and discomfort, in knowing how to "relax into the effort".
Many, many guitar players play with a great deal of tension that they are completely unaware of. This tension is throughout their entire body, and severely limits what they are able to do with their fingers. In fact, it is just like wearing a strait jacket. The upper torso gets completely involved in a constricting tightening of all muscles (usually accompanied by constriction of the breath). Attention is withdrawn from the body and this uncomfortable sensation, and the player manfully forces his way ahead. This only tightens the strait jacket.
This tension can only be undone by applying certain practice methods. These methods must be applied correctly and consistently over a period of months. When they are applied, they completely change what it feels like to play the guitar. Playing will feel easy and comfortable in a way that it never did before. And best of all, you will know how to keep getting better, and how to keep learning more difficult music, and make that easy as well.
However, the process of learning how to make our playing feel easy, and to play with relaxation, is much more complex than you might think. It is not about "eliminating" all tension. "Tension" in and of itself, is not bad. We cannot move even one finger unless a muscle "tenses" and moves that finger. It is about learning to control the "tension-release" process of the muscles. And part of learning this control, and learning how to make our playing more comfortable, involves knowing how to force ourselves into even more uncomfortable conditions, and learning how to be comfortable in them.
There are times when the best way to solve a difficult problem on the guitar is to begin to work on a problem that is twice as difficult. I first realized this when I was in my early playing years, but dealing with some very difficult classical repertoire. The difficulty was holding bars for long periods of time, while the fingers were required to do long stretches and/or quick movements. I was having quite a difficult time being able to do this. The bar was held at the 5th fret, and I began practicing it down the neck, all the way to the 1st fret (where it was almost impossible to do it). After a good deal of this practice, I found that it was quite easy now to do it at the 5th fret.
The process went something like this: when I first tried that passage at the 5th fret, I thought "wow, this is hard". When I tried it at the 1st fret I thought "my God, this is impossible". Then, when I went back to the 5th fret, I thought "hmmm, this ain't so bad!"
By making the difficulty even more difficult, by "doubling the trouble" I found the original difficulty much easier! Now, it is important to understand that this applies mostly to difficulties rooted in the requirement for strength and stretch. It is much less applicable to matters of speed. And MOST IMPORTANTLY, the tendency to withdraw attention from the body and constrict the breath must be overcome by Intention and Attention during this type of practice. If this is not done, this type of practice will either yield little or no result, or actually be harmful. We must do our utmost, at the point of highest stress, to "relax into the effort", using rotating attention, posing, attention to breath, and all the other tools taught in "The Principles of Correct Practice For Guitar".
So, when you have a strength or stretch issue, you should devise an intelligent routine that gives the hand/arm and body in general the experience of a progressively increasing demand. The body must physically experience this in order to adapt to the challenge. The big HOWEVER is this: you MUST be paying attention to the whole body and your breathing through the entire process. You CANNOT allow the "strait jacket" to begin to tighten.
Strength & Stretch vs Speed
Strength and stretch develop gradually for players. And the fact is that many things feel easier as the years go by not because we have gotten any stronger or flexible, but simply because the overall level of body tension has decreased while playing, and we have learned to maximize passive resources in playing with greater skill (the use of the heavy arm, for instance, maximizing the passive resource of weight, rather than using the active resource of muscular effort).
The reason "double trouble" does not work for matters of speed (you don't improve that scale played at 100 bpm by practicing it at 200bpm!) is because "speed" is dependent upon entirely different processes and conditions than strength and stretch . Speed is the result of, we may say the byproduct of, precisely timed movements of the two sides of the body, and those movements must deliver precisely calibrated levels of force, to the guitar itself and to the string, in precisely calibrated directions. The ability to do this is what is called "skill" on the guitar, and it makes fast motion and fast notes possible.
This co-ordination is built in exactly the opposite manner from "double trouble". We must do super slow practice, then carefully work up our movements (the Basic Practice Approach in The Principles) in order to develop speed. In other words, the way to strengthen and improve 16th's at 100 is to strengthen and improve your 16th's at 80.
Even so, there is a place for some slight degree of pushing ourselves even in matters of speed, but not to as high a degree as we do for matters of strength and stretch. It can be useful to have our muscles experience the increased demand and subsequent tension of a higher speed, if, while doing so, we can maintain that degree of awareness that allows us to "relax into", at least to some extent, this increased demand, and the feeling of tension it generates. But we don't want to spend a lot of time doing this. It is more a test than a way to achieve a new ability for speed.
I will sometimes increase the speed, just to see where the flaws are, make them show themselves in stark relief, then go back down to slow speeds or no tempo to work on the imprecise movements. The careful approach to and slightly beyond what I have called "the working speed", with intense observation of the mechanics of what you are doing, gives you valuable information that you then take down to the lower levels of your practice, working with the seeds of what you saw manifested at your playing limit. You want to find out where the weak spots are in the music, and you want to find out as soon as possible, so you can see what is causing them, and then fix them with lower speed practice.
I usually give this analogy to students who are afraid to push themselves into areas of discomfort - Imagine you are building a racing car. You take it on the road to see how fast it can go. It starts shaking at 30 mph. You stick your head out the window to see what is going on. You see a rear tire about to fall off. Good, now you know you have to tighten up that tire if you want to go over 30. So, you go back to the shop, put the car up on the lift, and tighten the tire. Now, you take it back on the road, and it goes 45 mph before it starts to shake, and now its the front tire, so you take it back to the shop and fix it, and you have a faster car. I think you get the point. If you only stay down at 10 mph, you will never know where the weak points are. You want to make the machine "fail quickly", rather than contain hidden problems.
Notice that we do not make the car faster by working on it while it is on the highway. We have to take it back to the shop, open the hood and get to work. Similarly, we do not cause fundamental improvement in our playing by just playing, especially by just playing fast! Scientific, deliberate, and focused practice is necessary to do that. I hope you understand that now, and why it is so. There are many "tools" in our toolbox when it comes to improving our playing, and Double Trouble is one of them. Knowing how and when to use the large number of practice methods at our disposal is what practicing correctly is all about!