title: Bilateral deficit of voluntary quadriceps muscle activation after unilateral ACL tear.
abstract: OBJECTIVE
  The inability to fully activate the quadriceps femoris muscle voluntarily is known to accompany several different knee-joint pathologies. The extent of a voluntary-activation deficit in patients after isolated rupture of the anterior cruciate ligament (ACL), however, has been reported to be small or nonexistent, making it questionable if a voluntary-activation deficit is a relevant factor for these patients at all.
  
  
  METHODS
  In this study the ability to voluntarily activate the quadriceps femoris muscles was quantified in 22 male patients with arthroscopically-proven isolated ACL ruptures using an established highly sensitive twitch-interpolation technique. Furthermore, the maximal voluntary contraction force of the quadriceps muscle was obtained by isometric knee-joint torque measurements. The results were compared with an age-, gender-, and activity-matched control group.
  
  
  RESULTS
  There was a moderate but significant mean reduction in maximal voluntary activation (VA) in both the injured (VA: 83.9 +/- 2.3%, mean +/- SEM) and uninjured side (VA: 84.7 +/- 2.2%) in comparison with controls (VA: 91.1 +/- 0.8%). However, of the patients the 23% who presented a considerably reduced voluntary-activation of less than 80% were mainly responsible for the significant mean deficit.
  
  
  CONCLUSIONS
  The deficit of isometric muscle strength on the injured side compared with that of controls was explained by the voluntary-activation deficit and a true muscle weakness. On the other hand, the diminished muscle strength of the uninjured side was explained sufficiently by the voluntary-activation deficit alone. Considering the bilateral voluntary-activation deficit, functional muscle tests might not be valid when the uninjured extremity serves as reference.
authors.affiliation: Department of Orthopedics, Otto-von-Guericke University, Magdeburg, Germany. DIETMAR.URBACH@MEDIZIN.UNI-MAGDEBURG.DE
authors.forename: D
authors.initials: D
authors.lastname: Urbach
authors.forename: W
authors.initials: W
authors.lastname: Nebelung
authors.forename: H T
authors.initials: HT
authors.lastname: Weiler
authors.forename: F
authors.initials: F
authors.lastname: Awiszus
mesh_terms: D000293:Adolescent; D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D012421:Rupture; D013848:Thigh