title: Dynamic knee stability and ballistic knee movement after ACL reconstruction: an application on instep soccer kick.
abstract: OBJECTIVE
  The instep soccer kick is a pre-programmed ballistic movement with a typical agonist-antagonist coordination pattern. The coordination pattern of the kick can provide insight into deficient neuromuscular control. The purpose of this study was to investigate knee kinematics and hamstrings/quadriceps coordination pattern during the knee ballistic extension phase of the instep kick in soccer players after anterior cruciate ligament reconstruction (ACL reconstruction).
  
  
  METHODS
  Seventeen players from the Portuguese Soccer League participated in this study. Eight ACL-reconstructed athletes (experimental group) and 9 healthy individuals (control group) performed three instep kicks. Knee kinematics (flexion and extension angles at football contact and maximum velocity instants) were calculated during the kicks. Rectus femoris (RF), vastus lateralis, vastus medialis, biceps femoralis, and semitendinosus muscle activations were quantified during the knee extension phase.
  
  
  RESULTS
  The ACL-reconstructed group had significantly lower knee extension angle (-1.2 ± 1.6, p < 0.021) and increased variability (1.1 ± 1.2, p < 0.012) when compared with the control group. Within the EMG variables, the RF had a significantly greater activity in the ACL-reconstructed group than in the control group (79.9 ± 27.7 % MVC vs. 49.2 ± 20.8 % MVC, respectively, p < 0.034). No other statistically significant differences were found.
  
  
  CONCLUSIONS
  The findings of this study demonstrate that changes in ACL-reconstructed individuals were observed on knee extension angle and RF muscle activation while performing an instep kick. These findings are in accordance with the knee stability recovery process after ACL reconstruction. No differences were observed in the ballistic control movement pattern between normal and ACL-reconstructed subjects. Performing open kinetic chain exercises using ballistic movements can be beneficial when recovering from ACL reconstruction. The exercises should focus on achieving multi-joint coordination and full knee extension (range of motion).
  
  
  METHODS
  III.
authors: Interdisciplinary Centre for the Study of Human Performance, Faculty of Human Kinetics, University of Lisbon, Lisbon, Portugal, ncordeiro@ipcb.pt.
authors: Nuno
authors: N
authors: Cordeiro
authors: Nelson
authors: N
authors: Cortes
authors: Orlando
authors: O
authors: Fernandes
authors: Ana
authors: A
authors: Diniz
authors: Pedro
authors: P
authors: Pezarat-Correia
mesh_terms: D000328:Adult; D059549:Anterior Cruciate Ligament Reconstruction; D056352:Athletes; D001696:Biomechanical Phenomena; D006801:Humans; D007718:Knee Injuries / Q000503:physiopathology / Q000601:surgery*; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D016059:Range of Motion, Articular; D020127:Recovery of Function / Q000502:physiology*; D012916:Soccer / Q000293:injuries*; D055815:Young Adult