Patients follow four clusters of participation in physical exercise after an ACL injury. Results from the NACOX cohort study

To explore how participation in physical exercise (PE) changes over time after an anterior cruciate ligament (ACL) injury. Additionally, to identify factors associated with participation in PE by analyzing longitudinal data. An explorative analysis of the NACOX study, a prospective multicenter cohort study. Patients with an acute ACL injury aged 15–40 years were followed for three years. The patients regularly reported participation in PE, knee function, new injuries, and surgeries. State sequence analysis and Hierarchical Cluster Analysis were used to analyze participation in PE. Clusters were compared using an analysis of variances, the Chi-square test, and Fischer's exact test. The study included 275 patients, 52 % female, with a mean age of 25 years. Four clusters were identified, varying from low to high participation in PE after an ACL injury. Clusters differed regarding the number of ACL reconstructions (ACLR) (p = 0.03); time from injury to ACLR (p = 0.03); patient-reported knee function at the follow-ups at 3 months (p = 0.02), 6 months (p = 0.02), and 12 months (p = 0.02) after injury; PE level before injury (p