PDA

View Full Version : Exercising for Osteoporosis discussion



Belinda Beck
07-02-1998, 03:36 AM
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
frequency,
>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
bbeck@leland.stanford.edu

-------------------------------------------------------------------
To unsubscribe send UNSUBSCRIBE BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://www.bme.ccf.org/isb/biomch-l
-------------------------------------------------------------------