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Re: Flat back paradox

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  • Re: Flat back paradox

    I'm glad that Dr Siff has succeeded in starting a wide-ranging
    discussion. I'd like to give my opinion on a number of points.

    1: He says that
    "... epidemiologically ... it appears that lumbar flexion under
    loading poses special risks to the intervertebral discs, so that it is
    generally advised that we avoid lifting with forward lumbar flexion

    The problem here is that the epidemiology is extremely poor,
    especially in terms of work related factors. I also suspect the model
    employed: it was observed that prolapsed intervertebral discs could
    cause sciatic pain via nerve root entrapment and therefore assumed
    that excessive loading on the disc would be likely to cause back pain.
    This ignores the musculature which, I submit, is much more likely to
    be damaged and to be the immediate cause of acute low-back pain.

    2: I'd be grateful if Dr Siff would point us to the studies he's
    referring to in regard to injuries suffered by weightlifters and
    powerlifters. Data on incidence rates, typical injury sites and
    severity would be interesting.

    3: I submit that, at the loads and velocities Dr Siff quotes for
    specific Eastern European lifters, the differential loading of the
    spine in the flexed and extended postures will have a very small
    effect on the total spinal load. In other words, for those lifters at
    those loads and speeds, back posture is largely irrelevant.

    4: It seems to me that the comments of Dr Hewett and Dr Voo in effect
    combine to say that we cannot generalise from a very small number of
    elite lifters to the whole of the workforce involved in manual

    5: A little history is in order: The following is from T. McClurg
    Anderson, "Human Kinetics and Analysing Body Movements", Heinemann
    Medical Books, 1951, Chapter XVII, "Bag Lifting', p 246:

    "... the load carrying efficiency of the back muscles is reduced by
    the flexibility of the spinal lever upon which they operate. When the
    spinal column is flexed and has to be extended against strong
    resistance the back muscles are more likely to be injured because they
    are simultaneously fulfilling two conflicting functions, i.e. (1)
    moving the spinal bones upon each other and (2) at the same time
    trying to stabilize the spine so that it may act as an effective
    lever. Further, in the flexed position the stresses imposed upon the
    spine are transmitted through the thick, soft discs of cartilage
    interposed between the spinal bones. Lifting with a straight back
    means that the extensor muscles of the back are essentially concerned
    in stabilising the spine and that stresses are transmitted more
    directly from bone to bone, with only thin plates of shock absorbing
    cartilage between the bones. ...with a bent back, the spinal joints
    are 'unlocked' and the thick discs of cartilage between the bodies of
    the spinal bones are compressed. [In a straight back] the joints
    between the posterior processes of the spinal bones are 'locked',
    pressure on the discs of cartilage is reduced, and stresses are
    transmitted more directly through stabilised bony structures. In the
    latter case the spinal muscles are more efficiently employed in moving
    the spinal lever as a whole."

    I've always thought the term 'straight' inappropriate for the back,
    but it is clear that advice to lift like this goes back at least as
    far as 1951. However, McClurg Anderson went on to weigh the relative
    benefits and limitations of the two methods. Other criticisms of the
    straight back advice go back at least as far as 1972. J.R. Brown
    wrote, in "Manual Lifting and Related Fields: an Annotated
    Bibliography", p 427:

    "The suggestion that lifting should be carried out at all times by
    means of a straight back and bent knees appears as a continuous thread
    running through the majority of works cited. Investigations by the
    present author and others have shown that the systems advocated in the
    official weight lifting manuals are incorrect, and that in many
    instances, methods advocated are likely to do more harm than good."

    6: It strikes me (I largely agree with both Ben Weitz and Jan-Paul van
    Wingerden), that we should avoid rigid prescriptions on "how to lift"
    but encourage workers to know their limits and lift in ways that they
    find safe and comfortable.
    Ergonomics and Work Psychology Section, Health and Safety Laboratory
    Broad Lane, Sheffield, S3 7HQ, UK.
    Tel +44 114 289 2594, Fax +44 114 289 2526