title: Effects of age and ACL reconstruction on quadriceps gamma loop function.
abstract: OBJECTIVE
  Both aging and anterior cruciate ligament (ACL) reconstruction are associated with strength deficits, which can in turn influence performance of activities of daily living. Thus it is informative to understand mechanisms underlying strength deficits. Age-related declines in strength follow reductions in muscle fiber numbers and size, whereas strength deficits following ACL reconstruction may be caused by the loss of intraligamentous mechanoreceptors. A common link between these conditions is the gamma spindle system, or the gamma loop. Appropriately applied vibration can affect the gamma loop by causing disruption of afferent feedback to a muscle and result in decreased force capabilities. We investigated the effect of age and ACL reconstruction on gamma loop function.
  
  
  METHODS
  Maximal isometric strength (MVC) and electromyography (EMG) of the quadriceps were quantified before and after vibration stimulation of the infrapatellar tendon of 3 groups: young healthy (n=4; mean age=23.8 yrs), young ACL reconstructed (n=7; mean age=22.4 yrs), and older healthy (n=4; mean age=66.1 yrs) individuals.
  
  
  RESULTS
  The quadriceps MVC, vastus lateralis EMG, vastus medialis EMG, and rectus femoris EMG declined significantly in the young healthy group following vibration stimulation to the infrapatellar tendon, which indicated an intact gamma loop. There were no changes in these variables for the old healthy and ACL reconstructed groups.
  
  
  CONCLUSIONS
  Gamma loop function was impaired in both the older and ACL reconstructed groups possibly due to either decreased muscle spindle sensitivity or the loss of mechanoreceptors.
authors.affiliation: University of Oklahoma, Department of Health and Exercise Science, Neuromuscular Research Laboratory, 401 Asp Avenue, Norman, OK 73019, USA. mgbemben@ou.edu
authors.forename: Michael S
authors.initials: MS
authors.lastname: Richardson
authors.forename: Joel T
authors.initials: JT
authors.lastname: Cramer
authors.forename: Debra A
authors.initials: DA
authors.lastname: Bemben
authors.forename: Randa L
authors.initials: RL
authors.lastname: Shehab
authors.forename: John
authors.initials: J
authors.lastname: Glover
authors.forename: Michael G
authors.initials: MG
authors.lastname: Bemben
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000704:Analysis of Variance; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D013848:Thigh; D014732:Vibration