title: Hip abductor function and lower extremity landing kinematics: sex differences.
abstract: BACKGROUND
  Rapid deceleration during sporting activities, such as landing from a jump, has been identified as a common mechanism of acute knee injury. Research into the role of potential sex differences in hip abductor function with lower extremity kinematics when landing from a jump is limited.
  
  
  OBJECTIVE
  To evaluate sex differences in hip abductor function in relation to lower extremity landing kinematics.
  
  
  METHODS
  2 x 2 mixed-model factorial design using a between-subjects factor (sex) and a repeated factor (test).
  
  
  METHODS
  University laboratory.
  
  
  METHODS
  A sample of convenience consisting of 30 healthy adults (15 women, 15 men) with no history of lower extremity surgery and no lower extremity injuries within 6 months of testing.
  
  
  METHODS
  Landing kinematics were assessed as subjects performed 3 pre-exercise landing trials that required them to hop from 2 legs and land on a single leg. Isometric peak torque (PT) of the hip abductors was measured, followed by an endurance test during which subjects maintained 50% of their PT to the limits of endurance. After a 15-minute rest period, subjects completed a 30-second bout of isometric hip abduction, from which we calculated the percentage of endurance capacity (%E). Immediately after exercise, subjects completed 3 postexercise landing trials.
  
  
  METHODS
  PT, %E, and peak joint displacement (PJD) of the hip and knee in all 3 planes of motion.
  
  
  RESULTS
  Women demonstrated lower PT values (5.8 +/- 1.2% normalized to body weight and height) than did their male counterparts (7.2 +/- 1.5% normalized to body weight and height, P = .009). However, no sex differences were seen in %E. Women also demonstrated larger knee valgus PJD (7.26 degrees +/- 6.61 degrees) than did men (3.29 degrees +/- 3.54 degrees, P = .04). Women's PT was moderately correlated with hip flexion, adduction, and knee valgus PJD; however, PT did not significantly correlate with men's landing kinematics. Regardless of sex, hip flexion (P = .002) and hip adduction (P = .001) were significantly increased following the 30-second bout of exercise.
  
  
  CONCLUSIONS
  Women demonstrated lower hip abductor PT and increased knee valgus PJD when landing from a jump, potentially increasing the risk of acute knee injury. Furthermore, correlations between hip abductor strength and landing kinematics were generally larger for women than for men, suggesting that hip abductor strength may play a more important role in neuromuscular control of the knee for women.
authors.affiliation: University of Kentucky, Lexington, KY 40504, USA. cjaco@lexclin.com
authors.forename: Cale A
authors.initials: CA
authors.lastname: Jacobs
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Uhl
authors.forename: Carl G
authors.initials: CG
authors.lastname: Mattacola
authors.forename: Robert
authors.initials: R
authors.lastname: Shapiro
authors.forename: William S
authors.initials: WS
authors.lastname: Rayens
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001265:Athletic Injuries / Q000503:physiopathology / Q000517:prevention & control; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D035002:Lower Extremity; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology*; D011336:Probability; D016059:Range of Motion, Articular / Q000502:physiology*; D012494:Sampling Studies; D012680:Sensitivity and Specificity; D012737:Sex Factors; D013314:Stress, Mechanical; D016474:Weight-Bearing