Diurnal variation in physical activity and musculoskeletal injury risk across sex and habitual exercise timing among physically active students.

This study examined whether habitual exercise timing and sex are associated with lower-limb injury prevalence and frequency in physically active young adults. A total of 454 recreationally active university students (48% males; age = 22.1 ± 2.4 years) completed a validated survey assessing training exposure, experience, and injury history. Habitual physical activity timing was classified into three defined categories: morning (08:00-11:00), midday/afternoon (11:00-17:00), and evening/night (17:00-24:00). Group differences were examined using chi-square and log-linear analyses. Zero-inflated Poisson (ZIP) and multivariable logistic regression models were used to identify factors associated with injury counts and occurrence, adjusting for age, fat mass index (FMI), training load, and experience. Injury prevalence was higher in males than females (p = 0.048). Injury frequency differed across time-of-day categories (p = 0.004), with the highest burden among participants exercising evening/night. In ZIP models, males, exercising evening/night, and higher FMI were associated with higher injury counts, whereas older age was associated with fewer injuries. Logistic regression showed similar associations for injury occurrence (AUC = 0.74, 95% CI: 0.69-0.79). Lower-limb injury risk in young, physically active adults is consistently associated with habitual exercise timing, sex, and adiposity. These findings highlight the importance of considering exercise scheduling patterns and FMI in injury-prevention strategies.