On Jan 22, 9:06*am, Prisoner at War wrote:
On Jan 22, 11:36 am, "Cubit" wrote:



For the physiology, I think Gary Taubes' "Good Calories, Bad Calories" may
help.

The phrase seems ambiguous to me, thus, might need contextual clarification.

Indeed! *But it's such a popular sentiment, and when I just read it
again in "Runner's World Complete Book of Running" I just had to ask
and find out, once and for all...the usual context appears to suggest
that our bodies burn more fat as it becomes more "efficient," though
I've also read somewhere (Noakes?) that being more efficient means
that less calories are burned for the same work....

In trained long-distance runners, the working muscles rely on a
greater proportion of their energy from fat for a given effort level
(the fat/glucose mixture is richer, so to speak). They can run on
mostly fat at paces that require the less trained runner to burn
mostly glucose. This gives them a higher lactate threshold so they can
run faster without accumulating lactic acid. If you can run at a 5:00
mile pace (or better!) without lactic acid buildup, because you're
doing it on fat, then you can kick some serious ass in distance
running. Kicking serious ass makes you inefficient in terms of total
energy use. We can say that these trained athletes are efficient in
their use of glycogen relative to their power output and speed.

The other sense of efficiency, less calories burned for the same work,
comes from biomechanics and from maintaining a low body mass. In
racing a given distance, the intensity of your energy output (your
wattage, so to speak) is capped. If you go too fast too early, you
will blow up. So you have to produce the greatest performance (fastest
forward motion) on a fixed energy output. So yes, that kind of
efficiency is directly related to being competitive.

Efficient use of glycogen means your muscles can produce a high power
output and sustain it, and turning that into the best possible
performance means making the most efficient use of that power: not
wasting it on useless motions, or carrying extra mass.

But all of that has little to do with losing body fat. During steady
endurance work, your muscles burn intra-muscular fat, plus free fatty
acids. Free fatty acids are released from adipose tissue when you're
not exercising. Like for instance when you are sleeping. Or during the
recovery periods in interval training. Eating breakfast sends these
morning free fatty acids scurrying back into storage, which is why it
might be a good idea to exercise first.