here is an interesting study regarding posture....not only will it help with your health...it appears to develop self discipline, which in turn increases exercise performance
"Researchers found that students who were instructed to improve their posture for 2 weeks subsequently showed greater stamina on an unrelated task (squeezing a handgrip), compared to those who did not “exercise” their self control". [Muraven, M., Baumeister, R.F., and Tice. D.M. (1999). Longitudinal improvement of self-regulation through practice: Building sef-control through repeated exercise. Journal of Social Psychology 139, 446-457.]