Re: What makes muscles tired?

Steve Marshall <sdm@xxxxxxxxxxxxxxxxxxxx> wrote:

"Peter Ashby" <pashby@xxxxxxxxxxxxxxxxx> wrote i

Well there is already a drug that circumvents the body's efforts to make
you stop exercising in hot weather when your brain is getting too hot.
You won't see the first deaths in competition from its use in marathon
runners, watch the cycling world.

The big breakthrough in fatigue in endurance exercise has been the
discovery that you don't hit the wall (around 20miles in the marathon)
because you have run out of glycogen. It happens because the brain
senses that glycogen stores are lower than a certain level and because
the brain is an obligate glucose user it acts to conserve stocks. This
can be postponed by taking in glucose to raise blood glucose prior to
the 20mile point. You can get small sachets of flavoured glucose syrup
and modern sports drinks contain dextrose which does the same job. I
have tested the idea myself and it certainly seems to help on those long
runs close to or over 2hrs in duration.

What about muscle fatigue in us mere mortals that get aches after a short
distance? Is it the same thing happening or something quite different? I
can go on brisk walks for a few miles without too much bother. I try and do
occasional jogs to try and prepare myself for running and the legs really
tighten up after short distances.

The muscle groups used and the proportions are different between walking
and running. So that you can walk says nothing about how good you are at
running. The way to run further is firstly not to try and run too fast
and secondly to jog for a bit, walk for a bit, jog for a bit etc. The
aim is to increase the amount of jogging and decrease the walking.

Similarly in strongman competitions they hold weights for a minute or so
before the muscles give up and they have to drop the weight. Different
fatigue ?

That is ischemic fatigue, muscles at full contraction exclude blood
through pressure. After a while working muscles need oxygen, simple.

Endurance exercise is therefore different. I should perhaps have said
that trained runners tend to hit the wall around 20miles. I'm not out to
20miles yet so I tend to hit the wall after 2hrs of running. So I take a
glucose gel sachet around 1.5hrs and wash it down with whatever drink
I'm carrying.

Peter


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