title: Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises.
abstract: OBJECTIVE
  Although closed (CKCE) and open (OKCE) kinetic chain exercises are used in athletic training and clinical environments, few studies have compared knee joint biomechanics while these exercises are performed dynamically. The purpose of this study was to quantify knee forces and muscle activity in CKCE (squat and leg press) and OKCE (knee extension).
  
  
  METHODS
  Ten male subjects performed three repetitions of each exercise at their 12-repetition maximum. Kinematic, kinetic, and electromyographic data were calculated using video cameras (60 Hz), force transducers (960 Hz), and EMG (960 Hz). Mathematical muscle modeling and optimization techniques were employed to estimate internal muscle forces.
  
  
  RESULTS
  Overall, the squat generated approximately twice as much hamstring activity as the leg press and knee extensions. Quadriceps muscle activity was greatest in CKCE when the knee was near full flexion and in OKCE when the knee was near full extension. OKCE produced more rectus femoris activity while CKCE produced more vasti muscle activity. Tibiofemoral compressive force was greatest in CKCE near full flexion and in OKCE near full extension. Peak tension in the posterior cruciate ligament was approximately twice as great in CKCE, and increased with knee flexion. Tension in the anterior cruciate ligament was present only in OKCE, and occurred near full extension. Patellofemoral compressive force was greatest in CKCE near full flexion and in the mid-range of the knee extending phase in OKCE.
  
  
  CONCLUSIONS
  An understanding of these results can help in choosing appropriate exercises for rehabilitation and training.
authors.affiliation: American Sports Medicine Institute, Birmingham, AL 35205, USA.
authors.forename: R F
authors.initials: RF
authors.lastname: Escamilla
authors.forename: G S
authors.initials: GS
authors.lastname: Fleisig
authors.forename: N
authors.initials: N
authors.lastname: Zheng
authors.forename: S W
authors.initials: SW
authors.lastname: Barrentine
authors.forename: K E
authors.initials: KE
authors.lastname: Wilk
authors.forename: J R
authors.initials: JR
authors.lastname: Andrews
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D015444:Exercise / Q000502:physiology*; D005081:Exercise Therapy; D006801:Humans; D007700:Kinetics; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009068:Movement; D018482:Muscle, Skeletal / Q000502:physiology; D014891:Weight Lifting / Q000502:physiology*