title: Preventing fall-related vertebral fractures: effect of floor stiffness on peak impact forces during backward falls.
abstract: METHODS
  In vivo biomechanical study of 11 male volunteers.
  
  
  OBJECTIVE
  To measure the peak forces applied to the buttocks in a backward fall from standing, and to determine whether this force is lowered by reductions in floor stiffness.
  
  
  BACKGROUND
  Fall-related vertebral fractures are common and backward falls result in impact to the buttocks. Compliant flooring may reduce impact force and risk for vertebral fracture during a fall. However, we have little knowledge of the peak forces applied to the body during a backward fall, or how floor stiffness affects this force.
  
  
  METHODS
  Eleven males, mean age 25 +/- 5 (SD) years, were suddenly released from a backward lean of 15 degrees , falling backward onto the ground which was covered with 4.5, 7.5, or 10.5 cm of ethylene vinyl acetate foam rubber. We measured 3-dimensional impact forces applied to the buttocks at 960 Hz with a force plate. We used repeated measures analysis of variance and post hoc t tests to compare peak forces between conditions. We also modeled peak vertical force for falls onto a bare floor. RESULTS.: There was a significant difference in peak vertical force between falls onto the 10.5 cm foam condition compared with the 7.5 cm (P = 0.002) and 4.5 cm (P < 0.001) conditions. Peak vertical force (N) was (mean +/- SD) 5099 +/- 868, 4788 +/- 702, and 4544 +/- 672 for the 4.5, 7.5, and 10.5 cm foam conditions, respectively, and estimated at 6027 +/- 988 for the rigid (bare floor) condition. Compared with the bare floor, these foam floors provided, on average, 24, 20, and 15% force attenuation respectively.
  
  
  CONCLUSIONS
  In a backward fall onto the buttocks, peak impact forces are 6.4 to 9.0 times body weight in a fall onto a bare floor. Reducing floor stiffness using even a thin (4.5 cm) layer of foam may provide 15% vertical force attenuation during a fall onto the buttocks.
authors.affiliation: Injury Prevention and Mobility Lab, Simon Fraser University, Burnaby, Canada. msran@sfu.ca
authors.forename: Meena M
authors.initials: MM
authors.lastname: Sran
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Robinovitch
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control*; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D002081:Buttocks / Q000293:injuries / Q000502:physiology; D005430:Floors and Floorcoverings / Q000592:standards*; D006801:Humans; D008297:Male; D009068:Movement / Q000502:physiology; D011187:Posture / Q000502:physiology; D016103:Spinal Fractures / Q000503:physiopathology / Q000517:prevention & control*; D013314:Stress, Mechanical