title: Electromechanical delay after ACL reconstruction: an innovative method for investigating central and peripheral contributions.
abstract: OBJECTIVE
  The purpose of this study was to investigate the electromechanical properties of atrophied muscle in patients with anterior cruciate ligament (ACL) reconstruction and to examine the relationship of changes in these properties for a voluntarily elicited maximal isometric contraction and peripherally stimulated twitch contraction.
  
  
  BACKGROUND
  It is not known if, following ACL reconstruction, a prolonged reaction time to a sudden stimulus is due to impaired proprioception in the knee joint, a prolonged processing interval in the central nervous system, or a greater elasticity in the series elastic component of the quadriceps femoris.
  
  
  METHODS
  Seventeen patients were recruited 2 to 3 months following a unilateral ACL reconstruction. Both the involved leg (ACL-invo group) and the uninvolved leg (ACL-uninvo group) were studied. Twenty-two athletes (training group) and 18 control subjects (control group) were also tested. These subjects performed voluntary maximal isometric contraction (MVC) of the quadriceps femoris. Maximal twitch response was also elicited by a supramaximal electrical stimulation to the femoral nerve, and surface electromyograms were recorded from the vastus lateralis in all four groups.
  
  
  RESULTS
  Total reaction time for MVC in the ACL-invo group (250.47 ms) was prolonged compared to that of the control and training groups. Twitch response in the ACL-invo group (25.26 ms) was prolonged compared to that of the other three groups. Premotor time during both MVC and twitch response did not differ among the four groups. Electromechanical delay during MVC (53.62 ms) and the evoked electromechanical delay in twitch response (20.04 ms) were prolonged in the ACL-invo group as compared to the other three groups.
  
  
  CONCLUSIONS
  Prolonged electromechanical delay in twitch response may be due to peripheral physiological disruptions (eg, stiffness of the series elastic component, changes of peripheral muscle fiber-type composition, or a decrease in function of the excitation-contraction coupling process). A prolonged electromechanical delay in twitch response can also explain the prolonged electromechanical delay observed for MVC. These findings suggest that prolonged total reaction time in MVC, when secondary to a visual stimulus in atrophied human quadriceps femoris muscle after ACL reconstruction, may be principally due to prolongation of electromechanical delay produced by peripheral physiological alterations. However, the contribution of premotor time to prolonged total reaction time was not revealed. Our results do not completely eliminate the possibility that central nervous system processing time and other neural factors are involved in the prolongation of reaction time.
authors.affiliation: Institute for Human Science and Biomedical Engineering, National Institute of Advanced Industrial Science and Technology, Ibaraki, Tsukuba, Japan. f-kaneko@aist.go.jp
authors.forename: Fuminari
authors.initials: F
authors.lastname: Kaneko
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Onari
authors.forename: Kotaro
authors.initials: K
authors.lastname: Kawaguchi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Tsukisaka
authors.forename: Serge H
authors.initials: SH
authors.lastname: Roy
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D016118:Anterior Cruciate Ligament / Q000294:innervation* / Q000601:surgery*; D000070598:Anterior Cruciate Ligament Injuries; D001182:Arthroscopy / Q000009:adverse effects / Q000379:methods; D004576:Electromyography; D004594:Electrophysiology; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007718:Knee Injuries / Q000150:complications / Q000601:surgery; D008297:Male; D009431:Neural Conduction / Q000502:physiology; D017933:Peripheral Nervous System / Q000502:physiology; D011336:Probability; D016059:Range of Motion, Articular / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D019651:Plastic Surgery Procedures / Q000009:adverse effects / Q000379:methods; D012680:Sensitivity and Specificity