Greater circadian disadvantage during evening games for the National Basketball Association (NBA), National Hockey League (NHL) and National Football League (NFL) teams travelling westward.

We investigated the effects of a circadian disadvantage (i.e. playing in a different time zone) on the winning percentages in three major sport leagues in North America: the National Basketball Association, the National Hockey League and the National Football League. We reviewed 5 years of regular season games in the National Basketball Association, National Hockey League and National Football League, and noted the winning percentage of the visiting team depending on the direction of travel (west, east, and same time zone) and game time (day and evening games). T-tests and analysis of variance were performed to evaluate the effects of the circadian disadvantage, its direction, the number of time zones travelled, and the game time on winning percentages in each major league. The results showed an association between the winning percentages and the number of time zones traveled for the away evening games, with a clear disadvantage for the teams travelling westward. There was a significant difference in the teams' winning percentages depending on the travelling direction in the National Basketball Association (F2,5908  = 16.12, P < 0.0001) and the National Hockey League (F2,5639  = 4.48, P = 0.011), and a trend was found in the National Football League (F2,1279  = 2.86, P = 0.058). The effect of the circadian disadvantage transcends the type of sport and needs to be addressed for greater equity among the western and eastern teams in professional sports. These results also highlight the importance of circadian rhythms in sport performance and athletic competitions.