Chakolate <chakolateDeathToSpammers@gmail.com> wrote:
> Chris Malcolm <cam@holyrood.ed.ac.uk> wrote in news:4t7tr8Fvr49uU1
> @mid.individual.net:
>> It's the first thing I've found which really seems to be working in
>> the sense of recovering from the injury. It's now very much harder to
>> hurt my arms/elbows than it used to be, and the stabbing pains I used
>> to get sometimes lifting something as simple as a mug of tea have
>> entirely gone away.
> That's good to hear. I don't have any such ailments to recover from, but
> I do notice that when I keep up the weights and the leg machine (also in
> front of the tube) everyday things in general are easier. Getting in and
> out of the car, lifting Tristan or Sophie, lugging groceries up the
> stairs, all seem a bit less weighty.
Obviously the body has some threshold of muscle strain beyond which it
thinks the muscle isn't strong enough and needs to grow a bit. It also
shrinks muscles which you don't use. So your muscle size is actually a
dynamic balance between the body's eating up what you don't use, and
being reminded of how much muscle you need by what you do with it.
The threshold of how much muscle you add in response to how much strain
is controlled by hormones. Hence the taking of hormones by body
builders.
As we age the levels of these hormones drop. So as we age the size of
muscle our everyday activities give us drops, and unusual exertions
become harder. This starts off a vicious circle, because we then start
avoiding those unusually strenuous activities which have become
harder, and so our muscles get less worked than they used to, and get
weaker still.
I suspect that when we're young these thresholds are set so that an
activity level of X actually produces muscles capable of say 150% of
X. In other words, lifting something weighing X every day will give
you muscles which can actually lift half as much again without much
struggle.
I suspect that as we age that threshold eventually drops below
replacement point, so that lifting X every day only gives you muscles
capable of lifting 99% of X. So with the passage of time lifting X
becomes harder and harder until you give up doing it.
Hence, IMHO, the importance of exercising as you age. If you want to
go on being able to lift that shopping bag, open that jar, or indeed
get up out of that armchair, you're going to have to push yourself
regularly to do something stronger than that in order to be able to
keep on doing that easily.
Incidentally the same thing is true of bones. Our bodies are always
leaching away those bits of our bones that aren't being used
(stressed), and growing bone back in those places where stress is
felt, so like muscle, the strength of our bones is a dynamic balance
between continuous processes of loss and replacement. There is an
added problem with bones, which is that what stresses them is not only
the forces exerted on them by muscles, but shock loads, impact. A
tennis player or boxer will develop stronger bones than a weight
lifter with the same size of muscles because of the larger shock
loads.
As we age we bruise and strain more easily, so not only do we use our
muscles less, but we are also also more careful to avoid sudden
impacts. We don't like bumping into things, we get more scared of
falling over, we stop doing the odd bit of running or jumping down off
low things so our legs and spines get less impact walloping. So our
bones are subjected to a double loss of stress. Not only are they
subject to reducing muscular loads, but in addition reducing impact
loads.
In other words, use it or lose it becomes increasingly important as we
age.
--
Chris Malcolm
cam@infirmatics.ed.ac.uk DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[
http://www.dai.ed.ac.uk/homes/cam/] 
Mouth ulcer from a bisphosphonate 
Linear Mode
