Lead author Daniel Kruger of the University of Michigan and Susan Hughes of Albright College in Pennsylvania, said the tendency to fall asleep first after sex is associated with greater partner desire for bonding and affection.
"The more one's partner was likely to fall asleep after sex, the stronger the desire for bonding," Kruger said in a statement.
The study, published in the Journal of Social, Evolutionary and Cultural Psychology, examined 456 participants, who completed anonymous online surveys assessing experiences and desires after sex with partners. Participants then indicated "who falls asleep after sex?" and "who falls asleep first when going to bed not after sex?"
Participants' desires for partner expressions of emotional bonding, physical affection and communication were higher when their partners had greater tendencies to fall asleep first after sex, the researchers said.
In addition, the researchers found despite the common stereotype, it was not more common for men to fall asleep first after sex. Women, however, were more likely than men to fall asleep first if sex hadn't taken place.
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