PHYS THER
Vol. 86, No. 8, August 2006, p. 1092
The Bottom Line
Evan Johnson
Evan Johnson, PT, DPT, MS, OCS, MT, Assistant Professor of Clinical Physical Therapy, Program in Physical Therapy, Columbia University, New York, NY.
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What problems did the researchers set out to study, and why?
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Conflicting evidence exists on what strategy is most effective in preventing back injury during lifting. The researchers examined how low back loading is affected by lifting strategy and the size and height of the load being lifted. They hypothesized that placing one foot beside the load to be lifted while assuming a kneeling position with the contralateral limb would reduce spinal loading but would induce asymmetrical spinal loading when lifting wide loads.
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Who participated in the study?
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Twelve male subjects with no history of low back pain (mean age of 26.1 years, SD = 26.1).
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What new information does this study offer?
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Large extensor moments about the joints of the lumbar vertebral column are produced by the paravertebral musculature during lifting. These moments result in large compressive and shear forces acting between each pair of vertebrae, which may result in injury to the intervertebral disk, muscles, and ligaments. Although lifting from a squat position with the lumbar spine maintained in lordosis is a commonly taught strategy, there is little evidence to support that this posture reduces compressive and shear forces acting on the spinal segments. Existing evidence suggests that compressive and shear forces acting on the lumbar spine are most influenced by load moment, lifting speed, and acceleration. This study showed that the width of an object and the height from which an object is lifted are more important determinants of forces acting on the lumbar spine than the strategy used to perform the lift. The study further suggests that squatting may be an effective technique to reduce compressive forces acting at L5-S1 when lifting narrow loads, but straddling and stooping techniques are more effective at reducing compressive forces when lifting wider loads from the floor. Asymmetrical spinal loading and increased lateral shear force was induced in this study when subjects lifted loads using the kneeling straddle technique as described.
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How did the researchers go about the study?
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The authors of this study measured kinematics, ground reaction forces, and electromyographic trunk muscle activity as subjects lifted wide (600 mm) and narrow (300 mm) 20-kg boxes from two heights (290 mm and 50 mm). Researchers constructed a model that allowed them to calculate 3-dimensional forces acting on the lumbar spine for each of 4 lifting techniques in each of the tested conditions. The lifting techniques tested were squat lifting (lifting with a straight lumbar spine while flexing at the knees), stoop lifting (lifting with straight knees while flexing the lumbar spine), straddle lifting (straddling the load in standing with one foot to the side of the load and the other behind the load), and the kneeling technique (straddling the load with one foot to the side of the load while kneeling on the contralateral knee behind the load). Videotaped instruction, guided practice, and verbal cueing in lifting techniques were provided to all subjects prior to testing. The researchers combined kinematic data from light-emitting diode markers with anthropometric and force-plate data to construct a 3-dimensional model. This model was then utilized to estimate net moments and compression and shear forces occurring at the L5-S1 spinal intervertebral disk during testing.
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How might the results of this study apply to patients who are treated by physical therapists from this point forward?
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Physical therapists should advise patients to avoid lifting wide objects from the floor whenever possible. When patients are required to lift objects from floor level, adjusting the posture to the size and placement of a load during lifting to minimize the horizontal distance from the low back to the load is advisable, based on current evidence. Teaching a patient to kneel on one knee while straddling a wide load on the floor may reduce the compressive and shear forces acting on the lumbar spine during lifting by bringing the load close to the body without placing the lumbar spine in full flexion, as seen in the stoop technique. When objects are narrow enough to fit between the feet, squat lifting can reduce compressive forces on the spine.
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What are the limitations of the study, and what further research is needed?
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This study was performed on a small, homogenous sample of healthy, young men. The results are not generalizable to women or indi- viduals with back pain. Furthermore, the mechanics of the spine in older individuals who are likely to have degenerative changes of the spine may be different from the sample tested in this study. Finally, this study doesn’t account for individual variations in lifting techniques that may occur due to musculoskeletal issues (such as knee pain or muscle flexibility) or due to asymmetry in load placement.
[Kingma I, Faber GS, Bakker AJM, van Dieën JH. Can low back loading during lifting be reduced by placing one leg beside the object to be lifted? Phys Ther. 2006;86:1091–1105.]
Related Article
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Can Low Back Loading During Lifting Be Reduced by Placing One Leg Beside the Object to Be Lifted?
- Idsart Kingma, Gert S Faber, Anja JM Bakker, and Jaap H van Dieën
Physical Therapy 2006 86: 1091-1105.
[Abstract]
[Full Text]
[PDF]
Copyright © 2006 by the American Physical Therapy Association.
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