Working out with a group can boost your endorphin levels. Photo: crschmidt, Flickr

It's long been said that misery loves company. But researchers at Oxford University's Institute of Cognitive and Evolutionary Anthropology found that when people exercise together, they increase their levels of "happy" hormones, the endorphins that are your body's natural way to reduce pain and create the post-workout high that keeps you coming back for more.

The study, published in the British journal Biology Letters, speculates that these hormones are the biological foundation for the social reward we find in communal activities like religious rituals, dancing, laughing and your killer spin class.

"The exact features of group activity that generate this effect are unknown," said the study's lead author, Emma Cohen. "But this study contributes to a growing body of evidence suggesting that synchronized, coordinated physical activity may be responsible."

In the study, researchers had a dozen athletes, rowing solo or as a part of a six-person team, complete a strenuous workout on a virtual boat. After 45 minutes, the participants' resistance to pain was put to the test. In both groups, exercise increased their ability to tolerate the pain of a tight blood pressure cuff, but the solitary rowers withstood less pain than the rowers who exercised together.

"The results suggest that endorphin release is significantly greater in group training than in individual training, even when power output, or physical exertion, remains constant," said Cohen.

So next time you're tackling a tough workout, take a friend or two along -- you'll all feel happier when the hard work is done.

Ready to share your workout with friends? Here are some helpful tips for finding the right workout partner for you.