Your mom was right: posture is important! I love scientific studies that reaffirm the obvious: men and women are both attracted to arched backs.
The curve in the spine that allows the lower back to bend inward toward the belly is called lordotic posture. Previous studies have showcased the role the posture plays in signaling a female’s readiness to mate among a variety of animals, including rats, guinea pigs, sheep, cats, ferrets and primates.
“The perception of attractiveness and visual attention to the hip region suggests that lordosis or the arching of the back might signal human females’ proceptivity or willingness to be courted,” Pazhoohi said. “This also might explain why women wear high heel shoes and why wearing high heel shoes increases womens’ attractiveness.”
The research showed that an arched back increases attractiveness from any viewing direction, but especially from the side and rear.
Just to avoid confusion, an “arched back” and a “rounded back” are opposites. The image below is an arched back — this is what you want.
The next image is a rounded back — this is not what you want.
An arched back enhances attractiveness in any body position (standing, sitting, kneeling, lying down) as long as you maintain “normal body angles” and don’t arch in a ludicrous manner.
In addition to visual appeal, the angles of the wife’s back and pelvis are major elements of sexual positioning. For example, arching her back during doggy style will allow for deeper penetration — but in missionary position, arching will likely be counter-productive. By mastering the rotation of her back and pelvis, the wife will gain a lot of control over her sexual pleasure and help her husband consistently hit “the right spot”.