daf at bms.brookes.ac.uk writes:
I'm glad we got it osrted out where this was going eventually :-)
>>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).
What I found interesting though was that there didn't seem to be very
much in the way of intermediary processes. That the switch in fuel so
directly correlates with a change in speed. I guess I am constantly
suprised that such simple things actually happen. In any case the
interesting part of the study was that runners ran very close to their
limit in terms of how much glucose/glycogen was available, that there is
a feedback somehwere that gives you that information.
>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.i
Probably so, but it seemed like something fun to argue about :-)
Anybody want to talk about aerobic glycolysis in proliferating cells?
:-)
