I'm way out of my league here since I don't really understand any of this stuff, but that's not what I'm reading from the others' posts (or from the article Alfonso posted).
I think the term "efficient movement" is confounding because it lacks a proper definition when we are using it -- it depends on how you measure it, doesn't it?
One might consider efficient to be using the least amount of energy (I'm talking physical/caloric energy here) used in order to perform a task. In that sense, simply lifting a finger without using anything else in your body may actually be the most efficient way. After all, it does seem like recruiting your entire body to lift a single spoon is kind of silly and overdoing it, isn't it?
Actually, I just thought of a better example. There was a period of time when I was obsessed with how I walked and thought about why people walk/run the way they naturally do as opposed to the way a TaiChi person might walk, or how a soldier might march... since the way people normally walk involves constantly losing and regaining our balance. And the answer was, well, the way we naturally walk is actually the most efficient way to walk and burns the least amount of energy. But it's certainly not the way an internal guy might tell you to walk.
Again, to fall back to that article -- just a thought: efficiency may not actually be a requirement for internal movement... efficiency in movement may result from high-level training in internal movement, but it's hardly the goal nor is it the defining measure (hey, the cause and effect thing I mentioned earlier again!). Things like whole-body movement and maintaining balance/equilibrium/groundpath at all times may be more important concepts to an internal artist than efficient movement. It might even be that... just like a neophyte in external movement needs to undergo a lot of training to move efficiently in an external fashion, a neophyte in internal movement also needs to move efficiently in an internal fashion. That is, a beginner of internal movement may actually be incredibly inefficient (especially compared to an intermediate external guy) and burning a ton of energy, but as they get better, they become more efficient at internal movement. Drawing from this, you might even have a case for saying that an expert in external movement may be moving equally efficiently as an expert in internal movement... but they're moving efficiently in different ways.
Again, I don't claim for any of this to be remotely true -- just a thought.
Efficiency is not even the half of it! The onion has layers.
At a lower layer of refinement, you have structure and linear "jin" - learning to efficiently coordinate the body to lift things, as one unified action, so that at least you are efficiently conveying force end to end (where one end could say be the ground and another your hand holding the spoon) - to borrow terminology, you could call this a jin pathway or ground path, IIRC, in Mike's lingo. If you stop there, well, you're missing out on just about, well, everything. It just gets only more interesting from there.
Higher up in the onion, there are no more paths, your body is expressing all paths at all times, all meeting somewhere... guess where? And, in a sense, stuff no longer even travels through, it just rides on the surface. Nothing gets into you any more, no attacker nor spoon.
Then even higher up, you realize you can make all kinds of interesting things happen by manipulating the activity of stuff going on along the surface and all the crazy stuff that happens when conscious beings come in contact with it.
And hell, these are just the layers on the onion that I and others are learning about. There are probably lots of coolers layers we are just too dumb to comprehend at the moment.
I think in the end it is more about cool martial applications, particularly for aikido, than it is about efficiency. You become incidentally more efficient, but I was more efficient just by working linear jin. If all I wanted was efficiency, why would I be chasing aiki, when I could just perfect linear jin to get that? We are trying to become martial artists, I hope, and it is fair to say that the demands of martial art, compared to many other sports are just a bit different, like tennis is different than football is different than cycling. You can't quite lump all the training in with each other and say even they're all chasing after their own sorts of efficiency. Qualitative, they're all quite different, and, aside from some broad areas of overlap, there are vast areas of non-overlap and context-specific skills.