Objectives: This study determined the effects of temporal changes in unanticipated pre-landing stimuli on lower limb biomechanics and the impact of sex and limb dominance on these variables during single leg landings. We hypothesized that reductions in the time of pre-landing unanticipated stimuli, female sex, and the non-dominant limb would significantly increase high-risk landing biomechanics during unanticipated jump landings.
Methods: Twenty-six subjects (13 male and 13 female) had initial contact (IC) and peak stance (0% - 50%) phase (PS) lower limb joint kinematics and kinetics quantified during anticipated (AN) and unanticipated (UN) single leg (left and right) landings. Post landing jump direction was governed via one of two randomly ordered light stimuli, presented either prior to initiation of the jump (AN), or 600 ms (UN1), 500 ms (UN2) or 400 ms (UN3) immediately prior to ground contact.
Results: Statistically significant (p < 0.05) differences in IC hip posture and PS hip and knee internal rotation moments occurred in unanticipated compared to anticipated landings. Differences were not observed, however, among unanticipated conditions for any biomechanical comparisons. Significant (p < 0.05) differences in specific IC and PS hip and knee postures and loads occurred between sexes and limbs. Neither of these factors, however, influenced movement condition effects.
Conclusion: Unanticipated landings induce modifications in landing biomechanics that may increase ACL injury risk in both men and women. These modifications, however, do not appear overly sensitive to the timing of the unanticipated stimulus, at least within a temporal range affording a successful movement response. Expanding unanticipated training to include even shorter stimulus-response times may promote the additional central control adaptations necessary to maneuver safely within the random sports setting.