title: EXERCISES THAT FACILITATE OPTIMAL HAMSTRING AND QUADRICEPS CO-ACTIVATION TO HELP DECREASE ACL INJURY RISK IN HEALTHY FEMALES: A SYSTEMATIC REVIEW OF THE LITERATURE.
abstract: BACKGROUND
  Anterior cruciate ligament (ACL) injury is common among females due to many anatomic, hormonal, and neuromuscular risk factors. One modifiable risk factor that places females at increased risk of ACL injury is a poor hamstrings: quadriceps (H:Q) co-activation ratio, which should be 0.6 or greater in order to decrease the stress placed on the ACL. Exercises that produce more quadriceps dominant muscle activation can add to the tension placed upon the ACL, potentially increasing the risk of ACL injury.
  
  
  OBJECTIVE
  The purpose of this systematic review was to compare quadriceps and hamstring muscle activation during common closed kinetic chain therapeutic exercises in healthy female knees to determine what exercises are able to produce adequate H:Q co-activation ratios.
  
  
  METHODS
  Systematic Review.
  
  
  METHODS
  Multiple online databases were systematically searched and screened for inclusion. Eight articles were identified for inclusion. Data on mean electromyography (EMG) activation of both quadriceps and hamstring muscles, % maximal voluntary isometric contraction (MVIC), and H:Q co-activation ratios were extracted from the studies. Quality assessment was performed on all included studies.
  
  
  RESULTS
  Exercises analyzed in the studies included variations of the double leg squat, variations of the single leg squat, lateral step-up, Fitter, Stairmaster® (Core Health and Fitness, Vancouver, WA), and slide board. All exercises, except the squat machine with posterior support at the level of the scapula and feet placed 50 cm in front of the hips, produced higher quadriceps muscle activation compared to hamstring muscle activation.
  
  
  CONCLUSIONS
  Overall, two leg squats demonstrate poor H:Q co-activation ratios. Single leg exercises, when performed between 30 and 90 degrees of knee flexion, produce adequate H:Q ratios, thereby potentially reducing the risk of tensile stress on the ACL and ACL injury.
  
  
  METHODS
  2a- Systematic Review of Cohort Studies.
authors.affiliation: Walsh University, North Canton, OH, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Dedinsky
authors.affiliation: Walsh University, North Canton, OH, USA.
authors.forename: Lindsey
authors.initials: L
authors.lastname: Baker
authors.affiliation: Walsh University, North Canton, OH, USA.
authors.forename: Samuel
authors.initials: S
authors.lastname: Imbus
authors.affiliation: Walsh University, North Canton, OH, USA.
authors.forename: Melissa
authors.initials: M
authors.lastname: Bowman
authors.affiliation: Walsh University, North Canton, OH, USA.
authors.forename: Leigh
authors.initials: L
authors.lastname: Murray
keywords: Anterior cruciate ligament; electromyography; hamstrings; quadriceps; resistance training