Lay, B.S.1, Lee, M.J.C.1, Tidman, S.J.1, Lloyd, D.G.2, Bourke, P.D.3, & Alderson, J.A.1
Experts in sport have consistently demonstrated a number of perceptual advantages over lesser skilled athletes that afford them more time to execute perceptual-motor skills. No investigations of this "expert advantage" have been extended to sporting injuries. A number of studies of evasive sidestepping have demonstrated its association with non-contact anterior cruciate ligament (ACL) injuries. Moreover, biomechanical variables during unanticipated sidestepping in response to generic stimuli have been shown to increase ACL injury risk compared with pre-planned sidesteps. As yet, sidestepping in response to ecologically valid visual stimuli has not been investigated. This study attempted to maintain perception-action coupling within the controlled lab environment by examining sidestepping biomechanics of high- and low-level soccer players when evading projected 3D stereoscopic defenders (compared with planned and unplanned arrow stimuli).
A customised integrated stereoscopic system was used to present the stimuli and capture the three-dimensional motion of the sidestep, ground reaction forces and activity of eight knee muscles, of 15 high-level and 15 low-level soccer players during the sidestepping tasks. Participants sidestepped in response to a one-defender scenario (1DS), two-defender scenario (2DS), arrow-planned condition (AP) and arrow-unplanned condition (AUNP). Temporal constraints imposed by the stimuli conditions increased in difficulty from the AP, 1DS, 2DS to the AUNP. Lateral trunk flexion and hip abduction were measured. A kinematic model was used in conjunction with force plate data to investigate knee valgus loading. Muscle activation was measured during a pre-contact and weight-acceptance phase of the sidestep. Knee flexors-extensors co-contraction ratios were established.
Lateral trunk flexion, hip abduction and peak knee valgus moments increased when higher temporal difficulty was imposed by the stimuli during sidestepping. In the 2DS, high level players exhibited decreased hip abduction and knee valgus moments, and an earlier shift from a flexor dominant co-contraction strategy in pre-contact toward extensor dominance in weight-acceptance, compared with the low-level players.
Increased temporal difficulty imposed by the stimuli resulted in more injurious sidestepping biomechanics. Only the 2DS visual-perceptual condition was able to differentiate the sidestepping biomechanics of the high-level and low-level players, potentially due to its realism and high level of complexity. Using 3D stimuli to investigate sidestepping in a controlled environment addresses both the visual-perceptual and motor components of the manoeuvre. Implications for ACL injury aetiology are discussed together with further preliminary data systematically manipulating stimuli complexity (perception) and type of skill (action) within the experimental context presented here.