[Note: This post is not about internal and external martial arts, it's about two types of cuing during martial arts instruction.]
There are ideas and trends that make there way through the physical performance industry every so often, and what starts in either research laboratories or in high level training environments eventually trickles down to the general fitness population. Some turn out to be fads but some persist. At its core, the entire purpose of this blog is to report on those innovations as they might apply to traditional martial arts practice.
One popular 'innovation' that's been working its way around the performance training circuit lately is internal vs. external cuing. (I put innovation in scare quotes because nobody is claiming that these scientists have invented external cuing - the innovation is the careful distinction between the two types and the deliberate emphasis on one type over another.)
Cuing is just a general term for the kind of instructions you give someone to change their movement. Telling someone to keep their shoulder low when punching, reminding someone to straighten their back leg while in front leaning stance, even reminding someone to breathe.
None of this is new - I'm sure cuing is as old as training. Some recent research in neuroscience has focused on different types of cuing to try to determine which types, if any, are most effective. Step #1 is grouping cues into categories.
Internal cues are those that are directed towards the body. For example, suppose you want to get someone to jump higher. An internal cue might be, "forcefully extend your hips, knees, and ankles at the same time." Basically, any cue that references the parts of the body is internal.
External cues are those that are directed towards things outside the body. For the jumping example, "push the floor away" or "jump and reach towards this spot up on the wall."
Research has shown that, generally speaking, external cues are more effective than internal ones - that is, they result in greater improvements in performance. If you want a sprinter to drive their knees forward forcefully as they run, you're better off holding up some kind of shield and telling them to hit it as hard as they kind (an external cue), rather than telling them to drive the knee forward (an internal cue). Same desired result, different frame for the cue.
In addition to research results, a number of highly successful coaches have been reporting for a couple of years that they see better results with their high level athletes using external cues.
I highly doubt it's possible to teach martial arts without a LOT of internal cuing. I doubt it's possible to teach any highly technical, unnatural set of movements without a lot of internal cuing. It's fine to tell someone to jump higher by reaching for a high spot on the wall - jumping is a very natural motion, one for which most of us have a strong and efficient movement pattern. It's another thing to try to get someone to, for example, execute a spinning kick correctly without a lot of internal cues about body position and so forth.
However, where possible, with a little creativity a lot of training outcomes can be achieved with external cuing when you put effort into it.
For example, if a student isn't twisting their fist at the end of the punch, have them strike a target and tell them to try to spin the target as they hit it (instead of telling them to twist the fist). If a student is dropping their leg straight down after a front kick, have them practice kicking over a low (and soft) target so they have to retract properly or they'll trip over the obstacle (but don't tell them what to do other than saying that they need to clear the obstacle).
You'll give verbal instruction along with placing the items, but your words can focus on the outside - don't say, "retract the kick before putting the foot back down," just say, "kick over the target, then come back to your stance." If a student has a weak stance (for example, maybe they are standing in sanchin dachi with knees straight), push them a little bit from the front and see if they settle in a better stance when trying to resist the force (instead of just telling them to soften the knees). I suspect that some internal cuing will need to be added to reinforce all of these examples, but I also suspect that you can get pretty far on the external cues alone, or gradually switch over to using mostly external cues with intermediate and advanced students, saving the internal cues for beginners who really don't have even the most basic idea how to move their bodies.
I strongly suspect that better athletes need less internal cuing than worse athletes. One of the things that makes a 'good' athlete is a knack for solving spatial problems with their body. Good athletes are better at moving the right way. Bad athletes need more help.
In short, when teaching, try to use as much external cuing as you can, and use internal cuing as a last resort. Keep a notebook with cues that you like to use, and over time try to replace the internal cues with external ones whenever it's possible (it won't always be, but that's okay).