title: Quadricep and hamstring activation during drop jumps with changes in drop height.
abstract: OBJECTIVE
  Compare the muscle activation patterns of the quadricep-hamstring during drop jumps with increasing demands of drop heights.
  
  
  METHODS
  Observational.
  
  
  METHODS
  University biomechanics laboratory.
  
  
  METHODS
  Fifteen male and eight female college physical education students.
  
  
  METHODS
  Electromyographic activity of the rectus femoris (RF) and biceps femoris (BF) during the landing and takeoff phase of drop jumps from 20 to 60-cm heights. The ground contact time, vertical ground reaction force (vGRF), knee flexion angle during ground contact, and jump height after takeoff were also analyzed.
  
  
  RESULTS
  The activation of RF was higher in the drop jump from 60-cm than that from 20- and 30-cm (comparing 107.0 ± 45.9 to 82.3 ± 30.8 and 88.9 ± 38.9 %MVIC, P<.05) during the landing phase. Activation of BF remained similar across all drop heights. Drop jump from 60-cm resulted in greater contact time during takeoff phase and peak vGRF, and resulted in greater maximum knee flexion but straighter knee at ground contact than from lower drop heights.
  
  
  CONCLUSIONS
  At drop height of 60-cm, the altered knee muscular activation and movement patterns may diminish the effectiveness of plyometric training and increase the potential injury risk of knee.
authors.affiliation: Department of Physical Education, Chinese Culture University, Taipei, Taiwan.
authors.forename: Hsien-Te
authors.initials: HT
authors.lastname: Peng
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kernozek
authors.forename: Chen-Yi
authors.initials: CY
authors.lastname: Song
mesh_terms: D001696:Biomechanical Phenomena; D001827:Body Height / Q000502:physiology*; D004576:Electromyography; D005080:Exercise Test; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D007866:Leg / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology; D059385:Plyometric Exercise; D016059:Range of Motion, Articular / Q000502:physiology; D013223:Statistics as Topic; D018709:Statistics, Nonparametric; D013334:Students; D014495:Universities; D055815:Young Adult