As mentioned at the beginning of this thread, I have no Systema experience, but I'm amazed that nobody's pointed out the obvious flaws in David's argument. David, your words about expenditure of muscular energy, contending against gravity, et. al. are just as applicable to static postures as they are to relaxed and free movement.
As an experiment, try standing *unmoving* in a swordfighting posture--say, jodan kamae--for a half hour. Analyze how you feel. Then walk around the room twirling your blade for a half hour, moving in the most relaxed and comfortable manner possible. Which tires you more?
Y'see, gravity still exists when you're standing still. Your muscles still work when you're standing still. You still expend energy when you're standing still.
Of course, you will probably expend less energy and effort while unmoving, but the body also has a tendency to tense and freeze up a bit after too long in a static position. My guess would be that Systema posits the maintenance of a limber and relaxed posture as more combatively efficient than the static... in other words, an acceptable tradeoff for a minimal amount of additional energy expended.
Roberto Valenzuela
Owari Kan-ryu sojutsu (尾張貫流槍術)
Shinkage-ryu heiho (新陰流兵法)
"Be intelligent, but do not be artificially intelligent." --Kung Fu Proverb
"Culture Check: Korean Arts still determined to make indigenous martial history from 4,000 year old cave drawings. France counters by claiming Savaate developed from hunting woolly mammoths before Ice Age." --The Nth Degree