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.
Chris Brogden, Kelly Marrin, Richard Page and Matt Greig
Adam Jones, Chris Brogden, Richard Page, Ben Langley and Matt Greig
Context: Contemporary synthetic playing surfaces have been associated with an increased risk of ankle injury in the various types of football. Triaxial accelerometers facilitate in vivo assessment of planar mechanical loading on the player. Objective: To quantify the influence of playing surface on the PlayerLoad elicited during footwork and plyometric drills focused on the mechanism of ankle injury. Design: Repeated-measures, field-based design. Setting: Regulation soccer pitches. Participants: A total of 15 amateur soccer players (22.1 [2.4] y), injury free with ≥6 years competitive experience. Interventions: Each player completed a test battery comprising 3 footwork drills (anterior, lateral, and diagonal) and 4 plyometric drills (anterior hop, inversion hop, eversion hop, and diagonal hop) on natural turf (NT), third-generation artificial turf (3G), and AstroTurf. Global positioning system sensors were located at C7 and the mid-tibia of each leg to measure triaxial acceleration (100 Hz). Main Outcome Measures: PlayerLoad in each axial plane was calculated for each drill on each surface and at each global positioning system location. Results: Analysis of variance revealed a significant main effect for sensor location in all drills, with PlayerLoad higher at mid-tibia than at C7 in all movement planes. AstroTurf elicited significantly higher PlayerLoad in the mediolateral and anteroposterior planes, with typically no difference between NT and 3G. In isolated inversion and eversion hopping trials, the 3G surface also elicited lower PlayerLoad than NT. Conclusions: PlayerLoad magnitude was sensitive to unit placement, advocating measurement with greater anatomical relevance when using microelectromechanical systems technology to monitor training or rehabilitation load. AstroTurf elicited higher PlayerLoad across all planes and drills and should be avoided for rehabilitative purposes, whereas 3G elicited a similar mechanical response to NT.
Adam Jones, Richard Page, Chris Brogden, Ben Langley and Matt Greig
Context: The influence of playing surface on injury risk in soccer is contentious, and contemporary technologies permit an in vivo assessment of mechanical loading on the player. Objective: To quantify the influence of playing surface on the PlayerLoad elicited during soccer-specific activity. Design: Repeated measures, field-based design. Setting: Regulation soccer pitches. Participants: Fifteen amateur soccer players (22.1 [2.4] y), injury free with ≥6 years competitive experience. Interventions: Each player completed randomized order trials of a soccer-specific field test on natural turf, astroturf, and third-generation artificial turf. GPS units were located at C7 and the mid-tibia of each leg to measure triaxial acceleration (100 Hz). Main Outcome Measures: Total accumulated PlayerLoad in each movement plane was calculated for each trial. Ratings of perceived exertion and visual analog scales assessing lower-limb muscle soreness were measured as markers of fatigue. Results: Analysis of variance revealed no significant main effect for playing surface on total PlayerLoad (P = .55), distance covered (P = .75), or postexercise measures of ratings of perceived exertion (P = .98) and visual analog scales (P = .61). There was a significant main effect for GPS location (P < .001), with lower total loading elicited at C7 than mid-tibia (P < .001), but with no difference between limbs (P = .70). There was no unit placement × surface interaction (P = .98). There was also a significant main effect for GPS location on the relative planar contributions to loading (P < .001). Relative planar contributions to loading in the anterioposterior:mediolateral:vertical planes was 25:27:48 at C7 and 34:32:34 at mid-tibia. Conclusions: PlayerLoad metrics suggest that playing surface does not influence mechanical loading during soccer-specific activity (not including tackling). Clinical reasoning should consider that PlayerLoad magnitude and axial contributions were sensitive to unit placement, highlighting opportunities in the objective monitoring of load during rehabilitation.