The most interesting modern theory of posture (imo) is that of FM Alexander, The Alexander Technique[1] (a system that has influenced other systems, such as those of Feldenkrais). The Alexander Technique is notable for avoiding the approach of standing by force of will and rather standing naturally once one has retrained a faulty idea of one's position in space. Proper posture thus becomes "effortless" rather than being a matter of force, effort or will (Alexander's writings on how modern society miscalibrates basic human balance reflexes are worth a look also).
It is interesting to read the long heritage of the idea of standing by will - especially the similarities of the idea of Alexander and Hegel passage quoted in the article.
It is interesting to read the long heritage of the idea of standing by will - especially the similarities of the idea of Alexander and Hegel passage quoted in the article.
[1] https://en.wikipedia.org/wiki/Alexander_Technique