title: Vertical impact increase in middle age may explain idiopathic weight-bearing joint osteoarthritis.
abstract: OBJECTIVE
  To test the hypothesis that ground reaction force increases when a standard stepping task is performed in late middle age.
  
  
  METHODS
  Consecutive sample.
  
  
  METHODS
  Internal medicine practice.
  
  
  METHODS
  Thirty-six male patients (age range, 17-72yr) from an internal medicine practice.
  
  
  METHODS
  Subjects performed 20 consecutive footfall impacts onto a force platform while barefoot and while wearing shoes.
  
  
  METHODS
  Ground reaction forces were recorded for each footfall.
  
  
  RESULTS
  Impact is positively related to age both when barefoot (r = .84, p < .001) and when wearing shoes (r = .71, p < .001). Impact remains constant until age 50, after which it increases by 13.3% for barefoot subjects. Barefoot impact was significantly lower and less variable than impact when shod (barefoot = 1.18 body weight [BW]; shod = 1.22 BW; F(1,5) = 169.91, p < .001).
  
  
  CONCLUSIONS
  An increase in impact force during locomotion was identified that occurs in late middle age, when stability declines and idiopathic weight-bearing joint osteoarthritis develops. Because impact is negatively related to stability, the impact rise is probably caused by postural adjustments to instability resulting from irreversible neurologic decline. This heightened impact may account for the accelerated rate of weight-bearing joint osteoarthritis that begins in late-middle age.
authors.affiliation: Centre for Studies in Ageing, McGill University, Montreal, Quebec, Canada. steven.robbins@sympatico.ca
authors.forename: S
authors.initials: S
authors.lastname: Robbins
authors.forename: E
authors.initials: E
authors.lastname: Waked
authors.forename: N
authors.initials: N
authors.lastname: Krouglicof
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D000704:Analysis of Variance; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000503:physiopathology* / Q000534:rehabilitation; D004856:Postural Balance; D011187:Posture; D012775:Shoes; D016138:Walking / Q000502:physiology*; D016474:Weight-Bearing