I have been training regularly for about two years now and am interested in economy of motion and muscle efficiency, specifically training to use the minimum effort/muscles to accomplish the goal. What have you found to be the best avenue to approach this from?
I am late replying because I have been kicking this around in my head for the last couple of days without reaching a 'clear' answer or path. There may be one but for now I only have signposts to offer.
Repetition: In the context of endurance effort one could say that repetition is the mother of economy but it's not the only answer. The new runner fights himself with every step, falling forward and catching himself, while the experienced runner appears to float. Clearly it's not just the repetition because practice makes habit so the more directed and correct the practice the better one will adapt. Another way to look at it is that the experienced runner who decides that triathlons would be fun must spend an inordinate amount of time and attention on the new movements to develop any sort of economy and it will take years to overwrite the efficiencies learned by running. The body will naturally try to use those efficiencies on the bike and it won't work - the difference between a true cyclist on a bike and a triathlete on a bike is the subject of much spirited mocking by cyclists (I'm told). One of the climbers we had in here this year has done so much pulling his body automatically tries to "pull" to solve any problem, even an overhead press. For him to learn the economies of pushing, or, more precisely, to unlearn automatic 'pulling response' to all stimulus will take years.
Overload: Moving a heavy load is a very effective way to force the body to find the most efficient path because all unnecessary movement is immediately obvious (to the body). Do a heavy Turkish Get-up and notice how naturally the body moves from point of stability to point of stability and how little the KB or BB moves out of a straight up and down path. Now do it with a light load and notice how the much 'extra' movement the body allows, how sloppy you get because you are over-horse-powered for the load. Heavy Deadlifts or OHS teach form better than light loads can. The same idea may be used in the context of running or riding or cross-country skiing. Max VO2 intervals, i.e. high output, high HR but without high levels of acidity (so NOT anaerobic) develop not only the aerobic system but also teach neurological efficiency because a high load or high speed is used during the work periods. This is specifically training economy at 'race pace' but transfers across the board to lower intensities.
Threshold: Also in line with the above signpost is the idea that by bumping your threshold higher - no matter the context - you may operate at sub-maximal intensities in a relaxed manner (among other things). The closer you are to your maximum threshold the more stress is experienced and we are conditioned to be tense and coiled and ready for anything under those conditions (caveman fight/flight stuff). The hormonal response to operating at near max intensity is different than operating at 50% of max, and relaxed.
Fatigue: I attended a martial arts school where teaching began only after an hour or more of hard work had already been done. Some would say these are not the ideal learning conditions for technical movements with a big neurological component but the teacher's thesis was that pre-fatigue opened a direct pipeline to the learning center, removed all prejudice, removed the mind's standard questioning attitude, etc. On top of that, it also meant the student learned the movements without excess muscle tension because fatigue had removed the natural tendency for the body to do more than is necessary.
Attention: One of my first coaches, Steve Ilg, often reminded me to strive for a 'soft face'. A grimace denotes internal struggle - whether real or imagined - and by relaxing the face one begins to notice what other muscles may be unintentionally participating in the exercise or movement. Steep technical climbing is one of the best teaching tools there is in this sense because we often 'solve' problems with 90% of musculature involved when only 50% is needed. But the body can be taught, through pre-fatigue (when strong), or after a long layoff produces some general weakness, to solve problems with minimum muscle involvement and if the body experiences that enough it will begin to voluntarily limit engagement. The climber who is strong in the gym (weight room) addresses every problem with strength because it's a habit and strength is the hammer he has. The weak climber addresses every problem with technical skill and intelligent movement because it's a habit and technique is the hammer he or she has at hand. It is easier to make the technical climber strong than to make the strong climber thoughtful.
Of all the signposts I think this last is the most effective: constant awareness. Can I turn this off and still get the job done? The 'soft face' cue is one of the best tools in my bag, the relaxation associated with it is not limited to cheek and jaw ...