Type of unanticipated stimulus affects lower extremity kinematics and kinetics during sidestepping.

Including an unanticipated stimulus has significant impacts on lower extremity biomechanics during dynamic movements. It is unknown how a live, human defender affects lower extremity biomechanics. The purpose of this study was thus to determine the effects of two types of unanticipated stimuli (visual stimulus; defensive opponent) on lower extremity kinematics and kinetics in males and females during 45° sidestepping trials. Eight males and eight females completed two unanticipated stimuli sidestepping conditions. Numeric visual analog scales for reaction difficulty and movement realism were collected and analysed using a 2 × 2 mixed-model ANOVA. Three-dimensional hip, knee, and ankle kinematics and kinetics were measured during the stance phase of the sidestep and analysed using statistical parametric mapping. Participants reported greater difficulty and less realistic movements with the visual stimulus. Unanticipated stimulus main effects were observed for knee abduction angle, and hip extension and adduction, and knee extension and adduction moments. Sex main effects were observed for hip flexion, hip abduction, and ankle dorsiflexion angles, as well as hip abduction, ankle plantarflexion and ankle eversion moments and vertical ground reaction forces. Participants responded differently to two unanticipated stimuli. Careful consideration should be used when determining the type of unanticipated stimulus used.