title: Influence of physical activity-related joint stress on the risk of self-reported hip/knee osteoarthritis: a new method to quantify physical activity.
abstract: BACKGROUND
  The relationship between physical activity (PA) and the development of hip/knee osteoarthritis (OA) has not been clearly defined. The purpose of this study was to develop a method to quantify PA-related joint stress and to assess its influence on the risk of hip/knee OA.
  
  
  METHODS
  Participants in a large longitudinal study, without knee/hip OA (n = 5284), were asked about their PA participation in 1986. PA-related joint stress was calculated using information on the frequency, intensity, and duration of individual types of PA, and incorporated a quantification of joint stress. Self-reported, physician-diagnosed hip/knee OA was ascertained by survey in 1990, 1995, and 1999 (average length of follow-up: 12.8 years).
  
  
  METHODS
  The joint stress PA score was not associated with an increased risk of hip/knee OA. Also, among walkers and runners there was no association between the frequency, pace, or weekly training mileage and hip/knee OA. Older age, previous joint injury and surgery, and higher body mass index were confirmed as independent risk factors for hip/knee OA.
  
  
  CONCLUSIONS
  Participation in PA as an adult does not increase the risk of hip/knee OA and there does not seem to be a threshold of increasing risk with increased training among walkers and runners.
authors.affiliation: Division of Adult and Community Health, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, Atlanta, GA 30341, USA. ihootman@cdc.gov
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Hootman
authors.forename: Carol A
authors.initials: CA
authors.lastname: Macera
authors.forename: Charles G
authors.initials: CG
authors.lastname: Helmick
authors.forename: Steven N
authors.initials: SN
authors.lastname: Blair
mesh_terms: D005260:Female; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D015999:Multivariate Analysis; D015207:Osteoarthritis, Hip / Q000209:etiology* / Q000503:physiopathology; D020370:Osteoarthritis, Knee / Q000209:etiology* / Q000503:physiopathology; D012307:Risk Factors; D013314:Stress, Mechanical; D014481:United States