Large compressive preloads decrease lumbar motion segment flexibility.
The bending, shear, and torsion flexibilities of 13 intact adult lumbar motion segments (from 11 men, two women, 48-83 years of age) were compared under three different compressive preloads, 0, 2,200, and 4,400 N. Test forces and moments up to 160 N and 16 Nm were applied at the center of the upper end plate of the intact disc. A compressive preload of 2,200 N resulted in a significant decrease in motion segment flexibilities in all seven test directions (p less than 0.06) when compared with results obtained with no preload; the preload decreased flexibility 2.6, 4.5, and 6.1 times in bending, axial torsion, and shear, respectively. These results suggest that studies of internal trunk load-sharing between active and passive tissues during strenuous tasks, which engender large spine compressive loads, should take these changes in spine passive resistance into consideration.
Janevic
J
J
Department of Mechanical Engineering and Applied Mechanics, University of Michigan, Ann Arbor 48109.
Ashton-Miller
J A
JA
Schultz
A B
AB
D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D009068:Movement; D013314:Stress, Mechanical