Fashion and Posture

In her fascinating study on human posture, 8 Steps to a Pain-Free Back, Esther Gokhale reports that debilitating back pain is a distinctively Western, post-nineteenth century problem for which the fashion industry is partly to blame (see pages 10-15 in particular). Elaborating on this charge, she notes that, around the time of World War I, French fashion magazines began to feature models with a supposedly more relaxed and casual but quite unhealthy posture. The idea was that the previous, more upright and therefore more natural and healthy, stance was stiff, rigid, and passé. Today, she says, clothes are made to fit the newer, more unnatural positions, which we have long since habituated.

According to Gokhale, if we abandoned this bad posture in favor of that which prevailed in Western culture prior to the twentieth century and still prevails in indigenous populations, we would experience a number of positive changes: less or no back pain as well as relief in muscles and joints all over the body; more energy, stamina, and flexibility; less stress.

This raises a host of questions in my mind. First, if clothing manufacturers alter the way they cut fabric so it will lay correctly on people adopting a new, unhealthy posture, doesn't this mean it will no longer sit well on someone striving for the older, more salutary stance? In other words, when clothes change in this way, don't they start encouraging the bad posture rather than merely accommodating it?

Second, I want to know which types of clothing do this. Is it just the ones we immediately think of as casual (jeans, t-shirts, etc.)? Is it not these at all but other types of garments? Or is it all clothes, including suits and dress shirts? After all, even dress clothes have been modified for comfort over the years and this "comfort" would have to be defined by what has been comfortable according to the reigning (in this case, unhealthy) posture.

This whole topic is really just a side issue in Ms. Gokhale's larger discussion so she doesn't fully address these concerns and I'm having trouble finding other sources on the matter. Can anyone point me in the right direction?