Synchronization of behaviour has repeatedly shown to increase endorphin activity as measured by pain threshold (Cohen, Ejsmond-Frey, Knight, & Dunbar, 2010; Sullivan & Rickers, 2014). Although research on synchronous behaviour and the synchrony effect has noted instances of the synchrony effect in multiple physical activities (Cohen et al., 2010; Davis, Taylor, Cohen & Mesoudi, 2015; Kokal, Engel & Kirschner, 2011), it has only incorporated small group trials. Additionally no previous literature has investigated endorphin level subsequent to the immediate termination of exercise. The current study examined the effect of group size on the magnitude of the synchrony effect and explore the length of time the synchrony effect lasts. Thirty-three participants rowed 3 twenty minute time trials on a Concept II ergometer under three counterbalanced conditions - alone, paired and large group (n=12). Pain threshold, was assessed before, immediately post, 5 minutes post, and 10 minutes post each session. Contrary to previous research, a significant synchrony effect was not observed between the solo and group conditions. A significant positive change in pain threshold was reported at the 10 minute post exercise time point compared to the paired condition. This result suggests a longer lasting synchrony effect in a large group condition and that synchronous movement in large groups allows for individuals to exert themselves longer in such conditions
