title: Systematic review and meta-analysis of the effects of football heading.
abstract: OBJECTIVE
  The objective of this study was to provide a meta-analysis examining the effects of football heading.
  
  
  METHODS
  Meta-analytical review on football heading effects on neurocognitive performance, cognition and symptom reports.
  
  
  METHODS
  Combinations of the key terms were entered into the following electronic database search engines: Cochrane Libraries, PyscARTICLE, PyscINFO, PubMed, ProQuest, SPORTDiscus and Web of Science on 7 July 2016.
  
  
  METHODS
  The following inclusion criteria were used to determine eligibility for studies: (1) the study examined and reported on soccer athletes; (2) the population's age, sex and sport position was described; (3) cognitive function, symptoms, balance or other outcomes were quantitatively measured; (4) football heading exposure was quantitatively measured between at least two groups and (5) the study was written in the English language after December 1979.
  
  
  RESULTS
  The literature search process identified 467 unique studies. After applying exclusion criteria, 28 studies remained. Included studies had a total of 2288 participants (female participants =933, male participants =1355), aged 13-70 years. The overall results of random effects modelling of football heading were found to be inconclusive across all outcomes, groups and time points. No moderating variables related to methodological, sample or study characteristics were supported in the analysis; age was a potential moderating variable.
  
  
  CONCLUSIONS
  We provide the first meta-analytical review of football heading effects aggregated from multiple studies and extended findings from a recent systematic review of the effects of football heading. Our analysis indicates no overall effect for heading a football on adverse outcomes.
authors.affiliation: Department of Orthopaedic Surgery, UPMC Sports Medicine Concussion Programme, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Kontos
authors.affiliation: Department of Kinesiology and Recreation Administration, Humboldt State University, Arcata, California, USA.
authors.forename: Rock
authors.initials: R
authors.lastname: Braithwaite
authors.affiliation: Division of Adolescent Medicine, Seattle Children's Hospital, USA.
authors.forename: Sara P D
authors.initials: SPD
authors.lastname: Chrisman
authors.affiliation: Department of Orthopaedic Surgery, UPMC Sports Medicine Concussion Programme, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Jamie
authors.initials: J
authors.lastname: McAllister-Deitrick
authors.affiliation: Department of Orthopaedic Surgery, UPMC Sports Medicine Concussion Programme, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Larissa
authors.initials: L
authors.lastname: Symington
authors.affiliation: Department of Orthopaedic Surgery, UPMC Sports Medicine Concussion Programme, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Valerie L
authors.initials: VL
authors.lastname: Reeves
authors.affiliation: Department of Orthopaedic Surgery, UPMC Sports Medicine Concussion Programme, University of Pittsburgh, Pittsburgh, Pennsylvania, USA.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Collins
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001265:Athletic Injuries / Q000175:diagnosis* / Q000209:etiology; D015415:Biomarkers / Q000097:blood; D001924:Brain Concussion / Q000175:diagnosis* / Q000209:etiology; D003071:Cognition; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012916:Soccer / Q000293:injuries*; D055815:Young Adult
chemical_list: D015415:Biomarkers
keywords: Concussion; Football; Meta-analysis; Soccer