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Dog Metabolism

daf at bms.brookes.ac.uk daf at bms.brookes.ac.uk
Tue May 31 03:49:54 EST 1994


>It was shown that marathon runners seem to always run the marathon in
>very similar times, and as soon as you try to speed them up, e.g. with a
>treadmill, they reach an exhaustion point before finishing the marathon,
>and are forced to slow down.
>
>The interesting things was that the point where the unn er was forced to
>slow down conincided very closely with the switch from carbohydrate
>fuels (tho whether glucose or glycogen I can't remember) to fats.
>Carbohydrate usage actually translated very closley to a faster speed,
>and when forced to run on fats teh runner slowed down to about 70% of
>teh original pace.

The reason for this is that an ahlete performing at the limit of his/her
ability is, in a long-term aerobic event, limited by the rate of delivery
of oxygen to the tissues by the heart and lungs.  When the metabolisable
glucose in the muscles runs out and energy generation is from fat
oxidation, the oxygen consumption by the muscle remains more or
less constant.  However, fats have a lower energy yield per mole
of oxygen consumed than carbohydrates, so the muscle gets less ATP
per oxygen (in spite of the great advantage of fats in energy content
per unit weight).

Back to the original question about dogs.  I suspect the answer would be
more physiological than about regulation of metabolism.  The type of
muscle fibres, their blood supply and their innervation make a big
difference.  Anatomical differences and style of gait count for a lot
as well.

David Fell
daf at bms.brookes.ac.uk




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