Abstract:
Although the incidence of non-contact anterior cruciate ligament (ACL) injuries is greater among
women than men athletes, the factors that contribute to this greater risk of injury are not well
understood. One relevant question is whether decision making during landing influences the
biomechanical and neuromuscular factors thought to contribute to ACL injury, and whether these effects
differ as a function of task and sex. The purpose of this study was thus to examine the effects of decision
making on the neuromechanics of two-footed landing tasks in women and men.
Twenty-nine healthy young adults (13 women; 16 men) completed a series of two-footed drop
landing and drop-jump tasks under preplanned and decision-making conditions. Biomechanical and
electromyographic data were collected. Repeated measures ANOVA was used to determine the effect of
decision making on hip, knee, and ankle kinematics and kinetics, and on proactive and reactive muscle
activity, as a function of task and sex. Multiple linear regression was used to assess the relationship
between select knee biomechanical variables and proactive muscle activity.
Decision making had numerous effects on lower extremity kinematics, kinetics, and
neuromuscular control, many of which were task-specific. Under decision-making conditions, individuals
exhibited similar joint postures at initial ground contact and similar amounts of reactive muscle activity
across tasks. The majority of the observed modifications in neuromechanics suggested a default towards
the preplanned drop landing strategy under decision-making conditions. Some effects of decision making
on joint mechanics and reactive muscle activity varied with sex, although the extent to which these
dissimilar effects modified relative ACL loading is not known. Knee flexion at initial contact, peak knee
abduction, and peak knee adduction moment were significantly related to the proactive activity of
several, primarily lateral, muscles of the lower extremity, independent of task and decision-making
condition.
These results indicate that decision making influences landing mechanics and neuromuscular
control and that these effects are generally task-dependent and, in some cases, sex-dependent. The
results also suggest that, in both women and men, drop landings and drop-jumps performed under
decision-making conditions are no more dangerous, with respect to ACL loading, than preplanned drop
landings.
