Context: Clinical and functional assessments are performed regularly in sporting environments to screen for performance deficits and injury risk. Circadian rhythms have been demonstrated to affect human performance; however, the influence of time of day on a battery of multiple ankle injury risk factors has yet to be established within athletic populations. Objectives: To investigate the influence of circadian variation on a battery of tests used to screen for ankle etiological risk factors. Design: Randomized crossover design. Setting: University laboratory. Participants: A total of 33 semiprofessional soccer players (age = 24.9 [4.4] y; height = 1.77 [0.17] m; body mass = 75.47 [7.98] kg) completed 3 randomized experimental trials (07∶00, 12∶00, and 19∶00 h). Main Outcome Measures: Trials involved the completion of a standardized test battery comprising the Biodex Stability System, Star Excursion Balance Test, isokinetic inversion: eversion ratio, joint position sense, and a drop-landing inversion cutting maneuver. Results: Repeated measures analysis of variance revealed significantly (P < .05) lower values for all Biodex Stability System indicia; overall stability index (1.10 [0.31] a.u.), anterior-posterior (0.76 [0.21] a.u.), and mediolateral (0.68 [0.23]) at 12∶00 hours when compared with 07∶00 hours (1.30 [0.45] a.u.; 0.96 [0.26] a.u.; 0.82 [0.40] a.u.), respectively. However, no significant (P ≥ .05) main effects for time of day were reported for any other test. Conclusions: Circadian influence on ankle etiological risk factors was task dependent, with measures of proprioception, strength, and Star Excursion Balance Test displaying no circadian variation, indicating no association between time of day and markers of injury risk. However, the Biodex Stability System displayed improved performance at midday, indicating postural stability tasks requiring unanticipated movements to display a time of day effect and potential increased injury risk. Consequently, time of testing for this task should be standardized to ensure correct interpretations of assessments and/or interventions.
Keywords: screening; soccer; time of day.