> > ..2..The enlargement is not a cosequence of
> aerobics; the slower heartbeat or
> > pulse rate reflects greater efficiency

The heart's weight, volume, and left ventricle's
thickness and chamber size all increase as a result of
endurance training.  Cardiac muscle hypertrophies just
like skeletal muscle as a result of endurance
training.  At one time the this enlarged heart
condidtion known as "athlete's heart" was a cause for
concern because previous research indicated a
pathological state for increase in heart size.

The increase in left ventricle wall thickness and
contractility is a result of a higher blood plasma
volume due to endurance training.  This leads to a
larger filling of the left ventricle.  A larger
preload and end diastolic volume.

When comparing bodybuilders and endurance athletes,
the relative size of the heart and left ventricle is
larger in endurance trained individuals.(Milliken et
al.)

As a result of endurance training, Stroke volume(SV)
increases.(A greater filling of the LV and more
forcefull contraction)  A greater end diastolic volume
means more blood enters the left ventricle.  A greater
end systolic volume means more blood leaves the left
ventricle after contraction.  This is why enduracne
athletes typically have low blood pressure.

Moving on to heart rate.  Endurance training decreases
resting heart rate.  Period.  The actual mechanism is
not known but it works.  The gentleman whose tumors
are shinking might not know how it is happening, but
it is presumable due to paleo eating.

A-VO2 Differnce.  In response to endurance training,
the arterial O2 changes very little, but the Venous O2
has less O2 due to a greater O2 extracton at the
tissue level and more efficient distribution of blood
volume

One final note.
VO2 = SV x HR x a-vO2 difference.
At maximum exercise levels, an increase in SV and
increase in a-vO2 differnce leads to an increase in
VO2

Endurance training affects VO2

Wilmore and Costill. "Physiology of Sport and
Exercise"  Human Kinetics. 1994


>
> Yes, but what makes the heart more efficient?  It
> has been a long
> time since I read about this stuff, but what I
> recall is that the
> increased efficiency is mainly the result of greater
> stroke
> volume.  This is the result of enlargement, in
> highly aerobically
> trained individuals.
>
> >   But the size of a heart is not an indicator of
> its health. >>
> >
> > .3...an enlarged heart is not a sign of health but
> a sign of disease.
>
> Is that categorically true?  I'll have to do some
> digging, but
> I'm pretty sure that enlargement is not unusual in
> people who do
> a lot of aerobics, and not pathological either.
> When it occurs
> in untrained people, that's something else again.
>
> Todd Moody
> [log in to unmask]
>

=====
-kb.
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