title: Lumbopelvic landing kinematics and EMG in women with contrasting hip strength.
abstract: OBJECTIVE
  Hip muscle weakness has been associated with altered lower extremity mechanics and the increased likelihood of receiving treatment for low back problems, although biomechanical injury mechanisms focused on the trunk have not been investigated. The purpose of this study was to compare lumbopelvic kinematic variables and muscle activation of the trunk and gluteal muscles in females with strong and weak hip muscle strength during a demanding single-leg task.
  
  
  METHODS
  Twenty-two asymptomatic females were categorized into a strong or weak group (11 per group) as determined by isometric hip extension and abduction dynamometry profiles. Participants performed a single-leg landing task during which three-dimensional lumbopelvic kinematics and trunk (lumbar erector spinae, external obliques, and rectus abdominis) and gluteal (gluteus maximus and gluteus medius) muscle activities were recorded. Peak lumbopelvic angular displacement, total angular excursion, and mean and peak angular velocity during the first 0.5 s of landing were reported. Mean normalized EMG and muscle cocontraction index (between the lumbar erector spinae and the external obliques) were also reported.
  
  
  RESULTS
  Significant between-group differences existed for each of the following: peak displacement, excursion, velocity, and muscle activity. Differences in peak angular displacement occurred in the frontal plane, whereas excursion differences were observed in all planes. Differences in peak velocity were noted in the sagittal and frontal planes. Weaker subjects showed increased muscle activation (across all muscles except the rectus abdominis) and cocontraction index.
  
  
  CONCLUSIONS
  Individuals with diminished hip muscle strength exhibit greater lumbopelvic angular displacement, velocity, and muscle activity during the single-leg landing task. Future studies targeting hip strengthening may provide more insight to rehabilitation protocols as well as the relation between hip strength, low back motion, and muscle activity.
authors.affiliation: Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA. popovich@usc.edu
authors.forename: John M
authors.initials: JM
authors.lastname: Popovich
authors.forename: Kornelia
authors.initials: K
authors.lastname: Kulig
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D004576:Electromyography; D005260:Female; D006615:Hip / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008161:Lumbosacral Region / Q000502:physiology; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D010388:Pelvis / Q000502:physiology*; D013177:Sports / Q000502:physiology*; D055815:Young Adult