The Effect of Bye Weeks on Injury Event Rates in the Canadian Football League.

OBJECTIVE To determine the effect of bye weeks (no practices or games) on the injury event rate in the Canadian Football League (CFL). DESIGN Historical (retrospective) cohort study. SETTING CFL. PARTICIPANTS CFL athletes between 2011 and 2018. INTERVENTION CFL pseudorandom assignment of bye weeks each season (2011-2013: 1; 2014-2017: 2; 2018: 3). MAIN OUTCOME MEASURES Game injury incident rate ratio (IRR) in the week following a bye week compared with non-bye weeks. Sensitivity analyses: IRR for the 2 and 3 weeks following a bye week. We conducted exploratory analyses for combined game and practice injury events because we did not have the number of players exposed during practice. RESULTS The IRR was 0.96 (0.87-1.05), suggesting no meaningful effect of a bye week on the post-bye week game injury event rate. We obtained similar results for cumulative game injury events for subsequent weeks: IRR was 1.02 (0.95-1.10) for the 2 weeks following the bye week and 1.00 (0.93-1.06) for the 3 weeks following the bye week. The results were similar with 1, 2, or 3 bye weeks. However, the combined game and practice injury event rate was increased following the bye week [IRR = 1.14 (1.05-1.23)]. These results are expected if the break period results in medical clearance for preexisting injuries; increasing pain in these locations following the bye week would now be considered new injuries instead of "exacerbations." CONCLUSIONS Bye weeks do not appear to meaningfully reduce the injury event rate. Furthermore, there was no injury reduction when adding additional bye weeks to the schedule.