William Jones wrote:

>> Then why did these cyclists reach the failure point in about 150
>> minutes?  I'm missing something here.
>
>
> Your question is a little unclear, but I guess you're asking if the
> intensity was so low, why would the athletes be exhuasted after 2.5hrs?


Yes, that's it.

> That would be because all endurance exercise relies on glycogen to a
> certain
> extent. Even at low intensities, while fat is the predominant energy
> source,
> glycogen is being utilized.

And as I understand it, the amount of glucose used depends on the
intensity, and percent of V02 max is a measure of intensity.  So the
study of the cyclists tells us that trained cyclists reach the failure
point after 2.5 hours at 65% (I think it was) of V02 max.
Coincidentally, this is about the same amount of time it takes trained
runners (though not the very best runners) to complete a marathon, after
which they are pretty exhausted too.  So it might be reasonable to
suppose that marathoners run at 65% of V02 max, because if they went
much higher than that they wouldn't be able to finish.  If this is the
case, then I think we're talking about a pretty serious level of
exercise after all.

For endurance athletes, it's important to try to maximize use of fat,
and minimize use of glucose, because glucose is the scarcer resource,
and because glucose is burned anaerobically in fast-twitch fibers,
creating lactic acid.  So at least part of the "training effect" is just
this: getting the muscles to use more fat and less glucose at a given
level of intensity.  I think Phinney's research suggests that ketosis,
after a period of adaptation, is one way to do this.


Todd Moody
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