Inner power is defined differently for different people. I think it is a combination and blending of the 2 extremes of the 2 camps that appear on this thread. The spirituality comes from the humility of taking responsibility and letting others be on their own path.[/i]
I believe that Dan et. al. are using "internal (not inner) power" to refer to a set of musculoskeletal causes and effects, that has little or nothing to do with one's mental or spiritual state. I could be wrong about that, so hopefully they will correct me if I am -- but I don't think they've claimed the term "inner power", and I'm pretty sure they haven't claimed any spiritual component as such.