Skip directly to search Skip directly to A to Z list Skip directly to page options Skip directly to site content

NIOSHTIC-2 Publications Search

Search Results

Torso flexion loads and the fatigue failure of human lumbosacral motion segments.

Authors
Gallagher-S; Marras-WS; Litsky-AS; Burr-D
Source
Spine 2005 Oct; 30(20):2265-2273
NIOSHTIC No.
20028583
Abstract
Spine loads associated with lifting a 9-kg weight were estimated at three torso flexion angles (0, 22.5, and 45 deg), and lumbosacral motion segments were cyclically loaded using these loads until failure or to a maximum of 10,020 cycles. The objective was to simulate the postures and loads experienced by the lumbar spine during repetitive lifting of moderate weights in different torso flexion postures and to analyze the fatigue failure response of lumbosacral motion segments. Previous fatigue failure studies of lumbar motion segments have not reproduced the combination of spinal postures, loads, and load rates anticipated in different torso flexion postures during lifting tasks characteristic of those in occupational settings. Twelve fresh human lumbosacral spines were dissected into three motion segments each (L1-L2, L3-L4, and L5-S1). Motion segments within each spine were randomly assigned to a simulated torso flexion angle (0, 22.5, or 45 deg) using a partially balanced incomplete block experimental design. Spinal load and load rate were determined for each torso flexion angle using previously collected data from an EMG-assisted biomechanical model. Motion segments were creep loaded for 15 minutes, then cyclically loaded at 0.33 Hz. Fatigue life was taken as the number of cycles to failure (10-mm displacement after creep loading). Specimens were inspected to determine failure mechanisms. The degree of torso flexion had a dramatic impact on cycles to failure. Motion segments experiencing the 0-deg torso flexion condition averaged 8,253 cycles to failure (+/-2,895), while the 22.5-deg torso flexion angle averaged 3,257 (+/-4,443) cycles to failure, and motion segments at the 45-deg torso flexion angle lasted only 263 cycles (+/-646), on average. The difference was significant at P<0.0001, and torso flexion accounted for 50% of the total variance in cycles to failure. Fatigue failure of spinal tissues can occur rapidly when the torso is fully flexed during occupational lifting tasks; however, many thousands of cycles can be tolerated in a neutral posture. Future lifting recommendations should be sensitive to rapid development of fatigue failure in torso flexion.
Keywords
Back-injuries; Manual-lifting; Injuries; Injury-prevention; Biomechanics; Low-back-disorders; Fatigue-failure; Torso-flexion; Posture; Materials-handling; Mining-industry; Construction
Contact
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236
CODEN
SPINDD
Publication Date
20051001
Document Type
Journal Article
Fiscal Year
2006
NTIS Accession No.
NTIS Price
Issue of Publication
20
ISSN
0362-2436
NIOSH Division
PRL
Source Name
Spine
State
PA; OH; FL
TOP