title: No association between surface shifts and time-loss overuse injury risk in male professional football.
abstract: OBJECTIVE
  To investigate frequent surface shifts and match play on an unaccustomed surface as potential risk factors for injury in Scandinavian male professional football.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Thirty two top-division clubs (16 Swedish, 16 Norwegian) were followed during seasons 2010 and 2011. The influence from (1) number of surface shifts (between artificial turf and grass) during five-match sequences, and (2) match play on an unaccustomed surface (other surface than on the home venue) on subsequent overuse injury risk was evaluated with generalized estimating equations (GEE). GEE results are presented with risk ratios and 95% confidence interval (CI). Injury rate was expressed as time loss injuries/1000h, and compared between groups with a rate ratio and 95% CI.
  
  
  RESULTS
  No association was found between the number of surface shifts and subsequent overuse injury risk (risk ratio 1.01, 95% CI 0.91-1.12). Furthermore, no difference was seen in subsequent overuse injury risk after match play on unaccustomed compared with accustomed surface (risk ratio 1.04, 95% CI 0.78-1.38). Grass clubs (grass installed at home venue) had a lower match injury rate when playing away matches on artificial turf compared with away matches on grass (rate ratio 0.66, 95% CI 0.40-0.89).
  
  
  CONCLUSIONS
  This study showed no association between surface shifts or playing matches on an unaccustomed surface and time-loss injury risk in professional football, suggesting that clubs and players can cope with such surface transitions.
authors.affiliation: Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, Sweden; Football Research Group, Sweden. Electronic address: karolina.kristensson@liu.se.
authors.forename: Karolina
authors.initials: K
authors.lastname: Kristenson
authors.affiliation: Department of Sports Medicine, Oslo Sports Trauma Research Center, Norwegian School of Sport Sciences, Norway.
authors.forename: John
authors.initials: J
authors.lastname: Bjørneboe
authors.affiliation: Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, Sweden; Football Research Group, Sweden.
authors.forename: Markus
authors.initials: M
authors.lastname: Waldén
authors.affiliation: Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, Sweden; Football Research Group, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Ekstrand
authors.affiliation: Department of Sports Medicine, Oslo Sports Trauma Research Center, Norwegian School of Sport Sciences, Norway.
authors.forename: Thor Einar
authors.initials: TE
authors.lastname: Andersen
authors.affiliation: Football Research Group, Sweden; Division of Physiotherapy, Department of Medical and Health Sciences, Linköping University, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Hägglund
mesh_terms: D056352:Athletes; D001265:Athletic Injuries / Q000209:etiology*; D012090:Cumulative Trauma Disorders / Q000209:etiology*; D005430:Floors and Floorcoverings; D006801:Humans; D008297:Male; D009664:Norway; D006109:Poaceae; D011446:Prospective Studies; D012307:Risk Factors; D012916:Soccer / Q000293:injuries*; D013548:Sweden
keywords: Epidemiology; Lower extremity; Soccer; Surface; Surveillance