Biol. Lett. doi:10.1098/rsbl.2009.0670 (2009)

Coordinated social activity, such as dancing or team sports, stimulates the brain to release high levels of mood-elevating endorphins that are believed to have a role in social bonding. But how can this be distinguished from the normal release of endorphins during exercise?

Emma Cohen of the University of Oxford, UK, and her colleagues looked at rowers training alone or with teammates on stationary rowing machines. Because measuring endorphins directly would require a spinal tap, the researchers instead used pain tolerance to gauge endorphin release after workouts. They found that rowers had greater increases in pain threshold after operating as a crew than when going solo.