title: Lower limb muscle pre-motor time measures during a choice reaction task associate with knee abduction loads during dynamic single leg landings.
abstract: BACKGROUND
  Female neuromuscular control during dynamic landings is considered central to their increased ACL injury risk relative to males. There is limited insight, however, into the neuromuscular parameters governing this risk, which may hinder prevention success. This study targeted a new screenable and potentially trainable neuromuscular risk factor. Specifically, we examined whether lower limb muscle pre-motor times, being the time between stimulus presentation and initiation of the muscle EMG burst, elicited during a simple choice reaction task correlated with knee abduction loads during separate single leg landings.
  
  
  METHODS
  Twenty female NCAA athletes had muscle (n=8) pre-motor time and knee biomechanics data recorded bilaterally during a choice reaction task. Knee biomechanics were also quantified during anticipated and unanticipated single (dominant and non-dominant) leg landings. Mean peak knee abduction loads during landings were submitted to a two-way ANOVA to test for limb and decision effects. Individual regression coefficients were initially computed between-limb-based muscle pre-motor times and peak abduction moments elicited during both the choice reaction and landing tasks. Limb-based linear stepwise regression coefficients were also computed between muscle PMT's demonstrating significant (P<0.05) individual associations and peak knee abduction moments during landings.
  
  
  RESULTS
  Peak knee abduction moments were significantly (P=0.0001) larger during unanticipated (51.25 (7.41) Nm) compared to anticipated (38.93 (9.32) Nm) landings. Peak abduction moments were significantly (P<0.05) correlated with bilateral medial gastrocnemius (r=0.62 dominant; r=0.63 non-dominant) and medial hamstring (r=0.77 dominant; r=0.79 non-dominant) pre-motor times elicited within the choice reaction task. Peak abduction moments during anticipated landings were significantly (P<0.05) correlated with both dominant (r=0.60) and non-dominant (r=0.59) medial hamstring pre-motor times. For unanticipated landings, non-dominant and dominant peak knee abduction moments were significantly correlated with medial hamstring pre-motor time (r=0.78) and combined medial gastroc and medial hamstring pre-motor times (r=0.94) respectively.
  
  
  CONCLUSIONS
  Medial muscle pre-motor times during a specific choice reaction task are associated with peak knee abduction loads during separate single leg landings. These muscles appear critical in stabilizing the knee against the extreme dynamic load states associated with such tasks. Targeted screening and training of supraspinal processes governing these muscle pre-motor times may ultimately enable external knee loads associated with landings to be more effectively countered by the overarching neuromuscular strategy.
authors.affiliation: School of Kinesiology, The University of Michigan, 401 Washtenaw Avenue, Ann Arbor, MI 48109, USA. mcleansc@umich.edu
authors.forename: Scott G
authors.initials: SG
authors.lastname: McLean
authors.forename: Bhushan
authors.initials: B
authors.lastname: Borotikar
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Lucey
mesh_terms: D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000502:physiology; D000070598:Anterior Cruciate Ligament Injuries; D056352:Athletes; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D004576:Electromyography / Q000379:methods; D005121:Extremities / Q000473:pathology*; D005260:Female; D006801:Humans; D007717:Knee / Q000473:pathology; D007718:Knee Injuries / Q000517:prevention & control; D009132:Muscles / Q000473:pathology; D012306:Risk; D013997:Time Factors