The synchrony effect (SE) refers to the finding that individuals’ endorphin levels (inferred through pain threshold) increase significantly after moving in synchrony with others compared to the same movement performed alone (Cohen et al., 2010). Considering the various outcomes attributed to endorphin activity (e.g., cooperation and cohesion (Dunbar & Schultz, 2012), the SE has tremendous implications for sport psychology. Although the SE has been repeatedly found, the research paradigm has only used rowing for 30-40 minutes to cause the SE (Cohen et al., 2010; Sullivan & Rickers, 2013; Sullivan et al., 2014). The current study was designed to ascertain the generalizability of the SE. Specifically, running on a treadmill for 20 minutes was used in the current design. Individuals (n= 60) participated in groups of three which were randomly assigned to one of two conditions – running in synchrony or running in a non-synchronized fashion. All runs took place on 3 adjacent treadmills. Pain threshold was measured before and after runs; change in pain threshold was used as a measure of endorphin activity. An independent samples t-test revealed no significant difference between the conditions (t (57) = 0.68, p > .05). Based on these results, the SE may be limited to longer and more vigorous activities than 20 minute runs. However, considering that synchronized activities as quick as 5 minutes have shown endorphin-affected outcomes (e.g., social cooperation (Valdesolo et al., 2010)), this may not be the case. Clearly, future research on the basic dynamics of the SE is needed to understand this fascinating phenomenon.