Travel-induced circadian shift between teams influences penalties in the National Hockey League

There is a growing recognition of the impact of circadian rhythms on athletic performance, when teams crossing multiple time zones play at a different circadian alignment than their opponents. This study aimed to examine the association between circadian differences between NHL teams and increased penalty behavior. Data from NHL games played between 2009 and 2021 (n = 27,642) were analysed. A travel-adjusted time zone was computed for both teams, from which a Difference in alignment between teams was calculated: Ahead, same as, and behind opponent. A one-way ANOVA was done with the Difference in alignment on the number and minutes of penalties and results were significant for both variables. Post-hoc analyses revealed that teams behind received significantly fewer penalties (p < 0.001) than teams ahead or in the same time zone as their opponents (p < 0.001) and had fewer penalty minutes than teams who were in the same time zone as their opponent (p = 0.002). These results suggest that teams playing at a later point in their circadian cycle than their opponents were given more penalties, which highlights the importance of professional organisations understanding the potential influence of circadian rhythms and travel on behavior and performance outcomes during games.