I've been thinking about this problem a lot the last few days, and how to best explain the way I understand it.
Here is the problem: we have a force coming at us (it's entering our body), I would like to give that force a number, to help keep things clear as we move through the problem. The force coming at us is "10".
We want to keep this force of "10" from pushing us over. To do this, we'll have to 'resist' the force with a force of our own that equals "10" or more.
Inside of our body, we have three things that can 'resist' forces. Two of these things provide 'inactive force' that is to say their structural integrity provides the force, like a table holding a drink. One of these things provides 'active force' that is to say it can change/vary the amount of force it provides. The things that provide 'inactive force' are bones and connective tissue. The things inside your body that can provide active force, are muscles. These are the only three things we have to resist an incoming force.
If in proper alignment, the bones can provide a force to resist a push with no muscular help at all. That is to say, if your body was propped into the right position, you wouldn't need any muscle to resist the incoming force. Connective tissue can do the same thing. If placed into the correct alignment, it can resist a force with no muscular contraction. However in order to move the bones and connective tissue into the correct positions we have to use our muscles. Also in order to "hold" the bones and connective tissue in these positions, the muscles have to work. Ideally we can find an arrangement that requires very little muscular tension to hold this position. This is the essence of "alignment" we arrange our bones and connective tissue in such a way that we don't require much muscle to hold them there. If we don't arrange our connective tissue and bones in a good way, we have to use more muscle to hold the position (the bone's and connective tissue aren't helping us as much).
If you've followed what I've written so far, and agree, we can look at my main question.
If you're not using the bones and connective tissue in good alignment with the ground, how is it that you are not using more muscle to resist the force??
Here are some diagrams I made to show what I feel is going on with muscles and bones in and out of alignment. It also shows what I would call these different alignments.
The first diagram shows how little muscle would have to work if the bones (and connective tissue) take some of the force. The bones in the arm arm aligned with the incoming force.
In the second diagram, the bones are not in alignment with the force. So the muscles have to work harder to support the force, as the bones (and connective tissue) are not taking some of the force)
In the third diagram, we see someone firing extra muscles that are not needed to resist the incoming force. I would say this is the kind of thing people are talking about when they describe "external" body use.