Being tall has its benefits and its disadvantages. If you’re a tall man and you’ve ever walked with a shorter significant other, then you might have noticed that you were walking slower at a slower pace. A new study finds that men only do this with a romantic partner, and that they do it at the expense of energy efficiency.

“It’s really men who do all the compromising,” Cara Wall-Scheffler, a biologist at Seattle Pacific University and lead author of the study, told USA Today. At least, that’s how it is with regards to male walking patterns when they’re with their partner. Wall-Scheffler and her team found that participants who walked alone or with friends of the same sex walked at their optimum speeds. When they walked with friends of the opposite sex, men tended to slow down a little and women sped up. But when the men walked with a romantic partner, they slowed down to match their partners speed.

“The men only slowed down to walk as slowly as women when they were in love with the women,” Wall-Scheffler told ABC Australia. “When they were holding hands they walked even slower.”

For the study, the researchers watched as 11 couples walked around a track in various combinations of two — together, with friends of both sexes, and alone. All of the men were similar in height and all the women were similar in height, but the women were all shorter than the men. They found that men had an average optimum walking speed of 1.53 meters per second and women had an optimum speed of 1.44 meters per second.  

The men slowed down seven percent from their optimal walking speed when walking with a romantic partner. This cost them energy efficiency, since they weren’t taking advantage of the distance they could go with each step. By reducing the amount of steps taken while walking, a person can reduce the amount of energy used up, Wall-Scheffler said.

But men may be sacrificing their energy for reproductive benefits without even knowing it. By allowing the woman to walk slower, he’s improving her chances of producing and caring for children. “By men slowing down, the female reproduction is protected, and that’s not something that is trivial,” Wall-Scheffler told the LA Times. “There is so much data that when women are able to reduce the amount of energy they spend walking, they have more children.”

Wall-Scheffler noted that in indigenous hunter-gatherer populations, women tend to walk together while men tend to walk alone, and sometimes with other men. She says that these behaviors could be seen cross-culturally and that they have a basis in evolution. “Whether or not selection has acted on this behavior so that we still see it among men today — I don’t know if I could go that far,” she told the LA Times.

Source: Wagnild J, Wall-Scheffler C. Energetic Consequences of Human Sociality: Walking Speed Choices among Friendly Dyads. PLOS One. 2013.