title: A step towards understanding the mechanisms of running-related injuries.
abstract: OBJECTIVE
  To investigate the association between training-related characteristics and running-related injury using a new conceptual model for running-related injury generation, focusing on the synergy between training load and previous injuries, short-term running experience or body mass index (> or < 25 kg m(-2)).
  
  
  METHODS
  Prospective cohort study with a 9-month follow-up.
  
  
  METHODS
  The data of two previous studies using the same methodology were revisited. Recreational runners (n = 517) reported information about running training characteristics (weekly distance, frequency, speed), other sport participation and injuries on a dedicated internet platform. Weekly volume (dichotomized into < 2h and ≥ 2 h) and session frequency (dichotomized into < 2 and ≥ 2) were the main exposures because they were considered necessary causes for running-related injury. Non-training-related characteristics were included in Cox regression analyses as effect-measure modifiers. Hazard ratio was the measure of association. The size of effect-measure modification was calculated as the relative excess risk due to interaction.
  
  
  RESULTS
  One hundred sixty-seven runners reported a running-related injury. Crude analyses revealed that weekly volume < 2h (hazard ratio = 3.29; 95% confidence intervals = 2.27; 4.79) and weekly session frequency < 2 (hazard ratio = 2.41; 95% confidence intervals = 1.71; 3.42) were associated with increased injury rate. Previous injury was identified as an effect-measure modifier on weekly volume (relative excess risk due to interaction = 4.69; 95% confidence intervals = 1.42; 7.95; p = 0.005) and session frequency (relative excess risk due to interaction = 2.44; 95% confidence intervals = 0.48; 4.39; p = 0.015). A negative synergy was found between body mass index and weekly volume (relative excess risk due to interaction = -2.88; 95% confidence intervals = -5.10; -0.66; p = 0.018).
  
  
  CONCLUSIONS
  The effect of a runner's training load on running-related injury is influenced by body mass index and previous injury. These results show the importance to distinguish between confounding and effect-measure modification in running-related injury research.
authors.affiliation: Sports Medicine Research Laboratory, Public Research Centre for Health, Luxembourg. Electronic address: laurent.malisoux@crp-sante.lu.
authors.forename: Laurent
authors.initials: L
authors.lastname: Malisoux
authors.affiliation: Department of Public Health, Section of Sport Science, Aarhus University, Denmark; Orthopedic Surgery Research Unit, Science and Innovation Center, Aalborg University Hospital, Denmark.
authors.forename: Rasmus Oestergaard
authors.initials: RO
authors.lastname: Nielsen
authors.affiliation: Sports Medicine Research Laboratory, Public Research Centre for Health, Luxembourg; Sports Clinic, Centre Hospitalier de Luxembourg, Luxembourg.
authors.forename: Axel
authors.initials: A
authors.lastname: Urhausen
authors.affiliation: Sports Medicine Research Laboratory, Public Research Centre for Health, Luxembourg.
authors.forename: Daniel
authors.initials: D
authors.lastname: Theisen
mesh_terms: D000328:Adult; D015992:Body Mass Index; D015987:Effect Modifier, Epidemiologic; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012420:Running / Q000293:injuries* / Q000502:physiology*; D013997:Time Factors
keywords: Effect-measure modification; Injury mechanism; Sports injury prevention; Training load monitoring