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Re: Exercising for Osteoporosis discussion

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  • LHBWeitz@aol.com
    The following is from an interesting discussion from the biomechincs list on the effects of various exercises on bone deposition in order to help
    Message 1 of 1 , Jul 4 4:27 AM
      The following is from an interesting discussion from the biomechincs list on
      the effects of various exercises on bone deposition in order to help
      patients/clients with osteoporosis:

      << Dear Justin,

      In response to your posting, I wanted to let you know that there is a large
      body of literature available regarding the effects of exercise loading on
      bone, particularly osteoporotic bone. Having just read a substantial
      proportion of it, and having a background in bone, I might be able to
      assist you with your question.

      >I am currently designing some resistance training programs for some
      >clients who suffer from mild to moderate degrees of osteoporosis. I
      >undertsnd that like muscle, bone tissue responds to the loads imposed
      >on it by getting bigger (denser) and/or stronger. Do these "loads"
      >have to be a compressive force applied through the bones eg during a
      >squat the vertebrae is compressed by the weight of the barbell and
      >upper body; or is it just a fact of the contracting muscles placing
      >stress (primarily a tension force) on the bones comprising the
      >articulating joint?

      The simplest answer to this question is no. Early studies of controlled
      isolated bone loading indeed indicated that compression primarily
      stimulated bone deposition and tension stimulated resorption. More
      recently, however, it has become clear that this is a very simplified
      interpretation of a rather complex bone adaptation process. The fact is,
      bone strain during physiological loading can rarely be described as either
      compressive or tensile. Different parts of the bone are usually exposed to
      different forms of strain. For example, in a squat, a vertebral body,
      although primarily loaded in compression, has components of tension by
      virtue of muscle and ligamentous attachment, and even as a result of trunk
      positioning which may not be completely vertical. The fundamental point is
      that will bone modify material and geometric properties in order to best
      withstand altered patterns of habitual loading with the greatest structural
      efficiency. For sites around bones that become routinely compressed, bone
      deposition is appropriate as an increase in bone mass will increase the
      resistance of the material to the compressive force. Tensile forces on the
      skeleton (eg. muscle insertion sites), can also be substantial and bone
      will accommodate these loads also. For example, observe the bone build-up
      (and underlying favourable trabecular orientation) at tendon insertion sites.

      >If these statements are correct, then exercises such as squats,
      >pushups and bench presses would be advisable for osteoporosis
      >sufferers due to the compressive loading of the bones, while chinups,
      >lat pulldowns and seated rows would be inadvisable due to the tension
      >forces through the bones.

      A number of people would argue these days that the forces from muscle pull
      on bones are equally, if not more important to bone mass maintenance or
      accretion than mechanical loading from the forces of gravity. Although the
      jury is still out on this issue, all of the exercises you mention could be
      considered "bone friendly" with the exception of one. I don't recommend
      seated rowing for osteoporotic patients as deep forward flexion may
      increase the risk of anterior vertebral body compression fractures. (Aside
      from this, chin ups and lat pull downs may actually place some compression
      and/or shear on the spine owing to the site of origin of the latissimus
      dorsi which is active during these activities.)

      Mark Swanepoel contributed the following:

      > If I remember correctly Prof Currey of the Univ of York
      >found something similar with bone, loading the ulnas of turkeys. If
      >he reads this message, it'd be interesting to hear about his work.
      >Anyhow, the upshot of this is that I am convinced that the repitition
      >magnitude, and rate of load change all play a role in determining
      >bone removal and deposition.

      A number of people have studied the effect of load magnitude, load
      frequency and rate of strain on the adaptive response of bone. (O'Connor,
      Lanyon, Rubin, McLeod, Gross). These aspects appear to interact with one
      another. That is, it was initially thought that increasing strain
      magnitudes was the optimal method of stimulating osteogenesis, until it was
      found that very low strains are osteogenic if applied at high rates.
      Strain gradients are also thought to be an important factor in the bone
      loading mileu.

      Mark also mentioned some cartilage literature for application to this
      issue. Although I believe it to be true that there may be similar
      mechanisms of adaption at the cellular level in connective tissue, I don't
      think it is wise to compare the responses of cartilage to loading to that
      of bone. Bone is a very dynamic tissue which has an extensive blood and
      nerve supply. The former feature undoubtedly enhances the ability of bone
      to adapt to load stimuli. Cartilage has a much poorer access to blood
      (appropriately, given its different physiological role), and does not
      undergo the remodeling process exhibited by bone. (I realise that recent
      discoveries in cartilage research indicate that it is a less inert tissue
      than previously thought, but I am trying to be concise - believe it or not!)

      Bryan Kirking wrote:

      >People with osteoporosis obviously do not have normal bone. I would
      question the benefit of your program design given your basic questions and
      think you may be opening yourself up to some serious liability issues here,
      not to mention that you could seriously hurt someone following a program
      that fails to correctly negotiate the complexities of these issues.

      I would respectfully disagree with these statements. In the first
      instance, what is normal bone? Osteoporosis, by definition, is merely a
      condition of substantially reduced bone mass with the presence of
      osteopenia-related fracture. The tissue is essentially the same. There is
      just less of it. Granted, it is normally a condition of the elderly and
      the ability of bone to respond to adaptive stimuli may be somewhat reduced
      as we age. But both animal and human exercise intervention trials have
      concluded that even the very old can derive skeletal benefit from increased
      levels of physical activity. For this reason I think you could be held
      liable if you DON'T recommend physical activity in therapy. Particularly
      in mildy osteoporotic individuals, it is not a dangerous approach, given
      appropriate screening for other medical conditions, careful exercise design
      and execution technique (such as excluding seated rows and other exercises
      which may increase the risk of crush fracture in comprimised skeletal
      components) and adequate supervision.

      As Lance Lanyon has been saying for a number of years, the most osteogenic
      form of bone loading appears to be that which is different to habitual
      patterns. So Justin, don't worry too much about exercises that may load
      bone in compression or tension. Think about activities that 1. constitute
      a change in loading for the individual (for some very sedentary people this
      may be as simple as walking, but as bone adaptation is site specific I
      recommend a more well-rounded resistance training [weights] plus impact
      loading [walking, aerobics, stair climbing] regimen), and 2. the patient
      is likely to comply with and will continue to do so throughout the rest of
      their life.

      Best regards,

      Belinda Beck, Ph. D.
      Stanford University
      Musculoskeletal Research Lab
      Veterans Affairs Medical Center, Menlo Park
      795 Willow Road, Bldg. 301
      Menlo Park, CA 94025
      U. S. A.
      Phone: (650) 493 5000 x22336
      Fax: (650) 617 2606

      Ben Weitz, D.C., C.C.S.P., C.S.C.S.

      There are only two truly infinite things, the universe and stupidity.
      And I am unsure about the universe.
      Albert Einstein
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