title: Hamstring strength and flexibility after hamstring strain injury: a systematic review and meta-analysis.
abstract: OBJECTIVE
  To systematically review the evidence base related to hamstring strength and flexibility in previously injured hamstrings.
  
  
  METHODS
  Systematic review and meta-analysis.
  
  
  METHODS
  A systematic literature search was conducted of PubMed, CINAHL, SPORTDiscus, Cochrane Library, Web of Science and EMBASE from inception to August 2015.
  
  
  METHODS
  Full-text English articles which included studies which assessed at least one measure of hamstring strength or flexibility in men and women with prior hamstring strain injury within 24 months of the testing date.
  
  
  RESULTS
  Twenty-eight studies were included in the review. Previously injured legs demonstrated deficits across several variables. Lower isometric strength was found <7 days postinjury (d=-1.72), but this did not persist beyond 7 days after injury. The passive straight leg raise was restricted at multiple time points after injury (<10 days, d=-1.12; 10-20 days, d=-0.74; 20-30 days, d=-0.40), but not after 40-50 days postinjury. Deficits remained after return to play in isokinetically measured concentric (60°/s, d=-0.33) and Nordic eccentric knee flexor strength (d=-0.39). The conventional hamstring to quadricep strength ratios were also reduced well after return to play (60:60°/s, d=-0.32; 240:240°/s, d=-0.43) and functional (30:240°/s, d=-0.88), but these effects were inconsistent across measurement methods.
  
  
  CONCLUSIONS
  After hamstring strain, acute isometric and passive straight leg raise deficits resolve within 20-50 days. Deficits in eccentric and concentric strength and strength ratios persist after return to play, but this effect was inconsistent across measurement methods. Flexibility and isometric strength should be monitored throughout rehabilitation, but dynamic strength should be assessed at and following return to play.
authors.affiliation: School of Exercise Sciences, Australian Catholic University, Melbourne, Victoria, Australia.
authors.forename: Nirav
authors.initials: N
authors.lastname: Maniar
authors.affiliation: School of Exercise and Nutrition Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Shield
authors.affiliation: School of Health, Sport and Professional Practice, University of South Wales, Pontypridd, Wales, UK.
authors.forename: Morgan D
authors.initials: MD
authors.lastname: Williams
authors.affiliation: School of Exercise Sciences, Australian Catholic University, Melbourne, Victoria, Australia.
authors.forename: Ryan G
authors.initials: RG
authors.lastname: Timmins
authors.affiliation: School of Exercise Sciences, Australian Catholic University, Melbourne, Victoria, Australia.
authors.forename: David A
authors.initials: DA
authors.lastname: Opar
mesh_terms: D000293:Adolescent; D000328:Adult; D005080:Exercise Test; D005260:Female; D000070633:Hamstring Muscles / Q000293:injuries* / Q000503:physiopathology; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007719:Knee Joint / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D000068958:Return to Sport / Q000502:physiology; D013180:Sprains and Strains / Q000503:physiopathology*; D019415:Torque; D055815:Young Adult
keywords: Hamstring; Injury; Review; Strength