title: Hamstring and Quadriceps Isokinetic Strength Deficits Are Weak Risk Factors for Hamstring Strain Injuries: A 4-Year Cohort Study.
abstract: A hamstring strain injury (HSI) has become the most common noncontact injury in soccer. Isokinetic muscle strength deficits are considered a risk factor for HSIs. However, underpowered studies with small sample sizes unable to determine small associations have led to inconclusive results regarding the role of isokinetic strength and strength testing in HSIs.
  
  
  
  To examine whether differences in isokinetic strength measures of knee flexion and extension represent risk factors for hamstring injuries in a large cohort of professional soccer players in an adequately powered study design.
  
  
  
  Cohort study; Level of evidence, 2.
  
  
  
  A total of 614 professional soccer players from 14 teams underwent isokinetic strength testing during preseason screening. Testing consisted of concentric knee flexion and extension at 60 deg/s and 300 deg/s and eccentric knee extension at 60 deg/s. A clustered multiple logistic regression analysis was used to identify variables associated with the risk of HSIs. Receiver operating characteristic (ROC) curves were calculated to determine sensitivity and specificity.
  
  
  
  Of the 614 players, 190 suffered an HSI during the 4 seasons. Quadriceps concentric strength at 60 deg/s (odds ratio [OR], 1.41; 95% CI, 1.03-1.92; P = .03) and hamstring eccentric strength at 60 deg/s (OR, 1.37; 95% CI, 1.01-1.85; P = .04) adjusted for bodyweight were independently associated with the risk of injuries. The absolute differences between the injured and uninjured players were 6.9 N·m and 9.1 N·m, with small effect sizes (d < 0.2). The ROC analyses showed an area under the curve of 0.54 and 0.56 for quadriceps concentric strength and hamstring eccentric strength, respectively, indicating a failed combined sensitivity and specificity of the 2 strength variables identified in the logistic regression models.
  
  
  
  This study identified small absolute strength differences and a wide overlap of the absolute strength measurements at the group level. The small associations between lower hamstring eccentric strength and lower quadriceps concentric strength with HSIs can only be considered as weak risk factors. The identification of these risk factors still does not allow the identification of individual players at risk. The use of isokinetic testing to determine the association between strength differences and HSIs is not supported.
authors.affiliation: Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar nicol.vandyk@aspetar.com.
authors.forename: Nicol
authors.initials: N
authors.lastname: van Dyk
authors.affiliation: Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar Oslo Sports Trauma Research Center, Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, Norway.
authors.forename: Roald
authors.initials: R
authors.lastname: Bahr
authors.affiliation: Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Rodney
authors.initials: R
authors.lastname: Whiteley
authors.affiliation: Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar The Sports Physician Group, Department of Sports Medicine, St Lucas Andreas Hospital, Amsterdam, the Netherlands Amsterdam Center of Evidence Based Sports Medicine, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Johannes L
authors.initials: JL
authors.lastname: Tol
authors.affiliation: Institute of Sport Exercise & Health, University College London, London, UK.
authors.forename: Bhavesh D
authors.initials: BD
authors.lastname: Kumar
authors.affiliation: Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar Sports Performance Research Institute New Zealand (SPRINZ), Millennium Institute of Sport and Health, Auckland, New Zealand.
authors.forename: Bruce
authors.initials: B
authors.lastname: Hamilton
authors.affiliation: Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Abdulaziz
authors.initials: A
authors.lastname: Farooq
authors.affiliation: Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar Department of Rehabilitation Sciences and Physiotherapy, Ghent University, Ghent, Belgium.
authors.forename: Erik
authors.initials: E
authors.lastname: Witvrouw
mesh_terms: D015331:Cohort Studies; D000070633:Hamstring Muscles / Q000293:injuries* / Q000503:physiopathology*; D006801:Humans; D016015:Logistic Models; D008297:Male; D053580:Muscle Strength / Q000502:physiology*; D052097:Quadriceps Muscle / Q000293:injuries* / Q000503:physiopathology*; D012307:Risk Factors; D012916:Soccer / Q000293:injuries* / Q000502:physiology; D013180:Sprains and Strains / Q000503:physiopathology*; D055815:Young Adult
keywords: football (soccer); hamstring muscle injury; injury prevention; isokinetic strength testing