WWI caused a marked declined in women’s slouching — a change which some doctors attributed to the war itself.

Said Dr. Eugene L. Fisk, director of the Life Extension Institute in June 1918:

The most gratifying physical change in women is in their posture. Time was, not so far distant, when the clouch was a fashionable attitude for women. This began in society, was seen on the stage, and was reflected widely among workingwomen. It was accentuated by the hobble skirt and the turkey trot, just before the war.

The last year has come like a breath of fresh air to the physical habits of all women. I believe the unconscious influence of the military largely accounts for it. The soldier has captured the popular imagination. The military bearing, the military salute, the military appearance appeal to the women even more quickly than to the men, and they react to it automatically in their physical manners. A girl who glides or slouches or minces along is no longer considered desirable by young men or envied by her associates.

What may make this doubly surprising is that WWI actually generally marked the end of corsets in America. Corsets forced women to sit up straighter with better posture, so one might think that their decline as a fashion would actually cause more slouching rather than less.

War as a Tonic for Jaded Feminine Nerves: Physicians Say They Are Now Treating Fewer Women Whose Ills Are Imaginary — Military Heels, Sensible Toes, and the Erect Carriage Instead of the Slouch

Published: Sunday, June 23, 1918