title: Acute first-time hamstring strains during slow-speed stretching: clinical, magnetic resonance imaging, and recovery characteristics.
abstract: BACKGROUND
  Hamstring strains can be of 2 types with different injury mechanisms, 1 occurring during high-speed running and the other during stretching exercises.
  
  
  OBJECTIVE
  A stretching type of injury to the proximal rear thigh may involve specific muscle-tendon structures that could affect recovery time.
  
  
  METHODS
  Case series (prognosis); Level of evidence, 2.
  
  
  METHODS
  Fifteen professional dancers with acute first-time hamstring strains were prospectively included in the study. All subjects were examined, clinically and with magnetic resonance imaging, on 4 occasions after injury: at day 2 to 4, 10, 21, and 42. The clinical follow-up period was 2 years.
  
  
  RESULTS
  All dancers were injured during slow hip-flexion movements with extended knee and experienced relatively mild acute symptoms. All injuries were located proximally in the posterior thigh close to the ischial tuberosity. The injury involved the semimembranosus (87%), quadratus femoris (87%), and adductor magnus (33%). All injuries to the semimembranosus involved its proximal free tendon. There were no significant correlations between clinical or magnetic resonance imaging parameters and the time to return to preinjury level (median, 50 weeks; range, 30-76 weeks).
  
  
  CONCLUSIONS
  Stretching exercises can give rise to a specific type of strain injury to the posterior thigh. A precise history and careful palpation provide the clinician enough information to predict a prolonged time until return to preinjury level. One factor underlying prolonged recovery time could be the involvement of the free tendon of the semimembranosus muscle.
authors.affiliation: Swedish School of Sport and Health Sciences, Stockholm, Sweden. carl.askling@ihs.se
authors.forename: Carl M
authors.initials: CM
authors.lastname: Askling
authors.forename: Magnus
authors.initials: M
authors.lastname: Tengvar
authors.forename: Tönu
authors.initials: T
authors.lastname: Saartok
authors.forename: Alf
authors.initials: A
authors.lastname: Thorstensson
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D003615:Dancing / Q000293:injuries; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D052580:Muscle Stretching Exercises / Q000009:adverse effects*; D010146:Pain / Q000209:etiology; D011446:Prospective Studies; D020127:Recovery of Function; D013180:Sprains and Strains / Q000175:diagnosis / Q000209:etiology* / Q000534:rehabilitation; D013848:Thigh