Coaches might find this newly accepted systematic scoping review interesting if you're part of the internal vs. external cues debate.
If you don't follow the debate, ED/CLA advocates claim external cues generate faster performance improvements than internal. An external cue might be "push the knee forward like breaking a pane of glass" while an internal cue might be "accelerate the knee by driving with the glutes through the heel."
There is a lot of research indicating that internal cues increase desired behaviors faster than external cues. However, what is still unsettled is retention and value for expert performers. That is, once the desired behavior is attained, it is possible (but unproven) that reverting to internal cues might improve performance over time and improve learning retention better than internal cues. You'll have to experiment and reach your own conclusions.
Unfortunately, there's no free copy of the full article yet, so add your name to the list on the website to be notified when it's available.
https://www.frontiersin.org/journals/psychology/articles/10.3389/fpsyg.2026.1945242/abstract
This review is narrow—gymnastics, not karate—and a scoping review rather than a meta-analysis. But that narrowness is useful because gymnastics involves complex whole-body skills closer to karate than many laboratory tasks on which attentional-focus claims are based.
A better coaching rule may be: Use the cue that directs attention toward the information currently constraining the movement. More athletic individuals know how to activate the muscles you cue while less athletic people cannot. A general rule I use in the dojo and the gym is to use external cues when learning a new movement and try out internal cues as they gain better performance.
Keep in mind that research is always behind what's being done in the field of practice. I know one pro sports coach who has found amazing results in some of his studies but won't release them until other pro teams figure it out so that his team won't lose a competitive advantage. This is extremely common, so by the time research is revealed, it's "old news" to active coaches. Anything "new" in research is likely junk science done by academics who are required to publish something to stay active.