title: Associations of isokinetic knee steadiness with hop performance in patients with ACL deficiency.
abstract: OBJECTIVE
  Contrary to the ample data available regarding the functional significance of isokinetic knee strength in patients with anterior cruciate ligament deficiency (ACLD), much less is known about the functional significance of isokinetic knee steadiness. This cross-sectional study aimed to evaluate, in patients with ACLD, the independent impact of isokinetic quadriceps and hamstrings torque steadiness on single-leg hop performance.
  
  
  METHODS
  Eighty-seven patients with unilateral ACLD participated. Patients performed isokinetic quadriceps and hamstrings steadiness and strength testing at 60°/s on an isokinetic dynamometer. Muscle steadiness and strength were represented by the wavelet-derived mean instantaneous frequency and peak value of the torque-time curves, respectively. To measure hop performance, patients performed a single-leg hop for distance and a 6-m single-leg hop for velocity.
  
  
  RESULTS
  One of two patients [n = 45 (51 %)] had a 10 % or greater difference in knee torque frequency levels between the ACLD and contralateral knees. In multivariable models adjusted for age, sex, knee pain, and knee strength, hamstrings steadiness was significantly related with hop velocity whilst quadriceps steadiness was significantly related with both hop distance and velocity. Variance decomposition analyses suggested that quadriceps steadiness was similar in importance to hamstrings strength on hop distance and velocity.
  
  
  CONCLUSIONS
  In patients with ACLD, isokinetic knee steadiness deficits were common and were independently associated with single-leg hop performance. Knee torque steadiness-a heretofore understudied variable-may prove a useful adjunct to conventional peak torque measurements by offering additional information to researchers and rehabilitation professionals about muscle performance and neuromuscular knee control.
  
  
  METHODS
  Prognostic studies, Level III.
authors.affiliation: Department of Physiotherapy, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore. puayonghao@gmail.com.
authors.forename: Yong-Hao
authors.initials: YH
authors.lastname: Pua
authors.affiliation: Department of Physiotherapy, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
authors.forename: Peck-Hoon
authors.initials: PH
authors.lastname: Ong
authors.affiliation: Department of Physiotherapy, Singapore General Hospital, Outram Road, Singapore, 169608, Singapore.
authors.forename: Jia-Ying
authors.initials: JY
authors.lastname: Ho
authors.affiliation: Department of Physiotherapy, The University of Melbourne, Melbourne, Australia.
authors.forename: Adam L
authors.initials: AL
authors.lastname: Bryant
authors.affiliation: School of Health Sciences Research, La Trobe University, Melbourne, Australia.
authors.forename: Kate
authors.initials: K
authors.lastname: E Webster
authors.affiliation: School of Exercise Science, Australian Catholic University, Melbourne, Australia.
authors.forename: Ross A
authors.initials: RA
authors.lastname: Clark
mesh_terms: D000328:Adult; D000070598:Anterior Cruciate Ligament Injuries; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D009068:Movement / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D019415:Torque
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