A causal and replication analysis of claims that jet lag affects team sport performance

It is broadly accepted that jet lag impacts human performance in sport; however, this has never been validated within a causal inference framework. Here, we used the potential outcomes framework to determine if jet lag, conditional on game time, causes collegiate football teams to under- or overperform expectations. We also attempted to replicate seminal noncausal analyses in professional football. Nine collegiate football seasons (2013-2022, omitting 2020), for a total of 6245 games were analyzed. A generalized additive model with penalized splines and independence weights was used to evaluate interactive causal effects of hours gained/lost in travel and game time on the probability of away teams beating the Las Vegas spread. Furthermore, we used our collegiate cohort to exactly replicate two previous studies purporting to show that NFL teams are adversely affected by jet lag. Jet lag's effects were compatible with the null hypothesis in both the causal analysis (P = .133) and noncausal replications. Practically, if the effects of jet lag are unclear, then it is also unclear whether interventions to treat jet lag in elite sport are warranted for teams crossing fewer than 3 time zones if the primary goal is to optimize winning.