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Fatigue failure of lumbar motion segments in a sample of working age specimens.

Gallagher-S; Marras-W; Litsky-A; Burr-D
American Industrial Hygiene Conference and Exposition, May 21-26, 2005, Anaheim, California. Fairfax, VA: American Industrial Hygiene Association, 2005 May; :16
Eighteen working age cadaveric lumbar motion segments (average age 49 years +/- 17 SD) were subjected to a fatigue loading regimen simulating lumbar loads when lifting a 9-kg box in three angles of torso flexion (0, 22.5, and 45 deg). Bone mineral content and bone mineral density were obtained from L1-L2 and L3-L4 motion segments each spine. Motion segments were loaded every 3 sec using a loading profile (compression, shear, and load rate) appropriate for each torso flexion angle, up to a maximum of 10,020 cycles. Bone mineral density for these specimens was 1.00 gram per square centimeter (+/- 0.25), and the average bone mineral content was 30.7 g (+/- 11.1). Spinal loads associated with lifting in different torso flexion angles affected the fatigue life of the motion segments, with all specimens in the neutral posture lasting the entire 10,020 cycles, while specimens exposed to the 22.5-deg torso flexion conditions lasted an average of 6,824 cycles and those exposed to the 45-deg conditions lasted an average of 4,209 cycles. Compared to an earlier investigation with older specimens (reported at last year's conference), these young specimens had higher bone mineral content and density and longer fatigue life compared to the older sample (which averaged 80 years of age). Lumbar level did not affect the number of cycles to fatigue failure. Results of this study suggest that spinal tissues will fatigue fail more quickly when lifting a given load in a flexed torso posture as opposed to a neutral torso posture.
Fatigue; Motion-studies; Age-factors; Manual-lifting; Injuries; Back-injuries; Posture; Ergonomics; Musculoskeletal-system; Injury-prevention
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236
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American Industrial Hygiene Conference and Exposition, May 21-26, 2005, Anaheim, California