Preventing fall-related vertebral fractures: effect of floor stiffness on peak impact forces during backward falls.
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.
Sran
Meena M
MM
Injury Prevention and Mobility Lab, Simon Fraser University, Burnaby, Canada. msran@sfu.ca
Robinovitch
Stephen N
SN
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