I think it is important that everyone remember that:

Cardiac output = HR * stroke volume

The ejection fraction is not in the equation.

Stroke volume increases if there is an increase in end-systolic volume
or a decrease in end-diastolic volume. The ejection fraction is simply
a function of these.

A normal heart has an ejection fraction above 60%. Ejection fractions
lower than 60% mean the person is starting to have heart failure.
Ejection fractions less than 50% are associated with increased
mortality and ejection fractions less then 40% represent moderate to
severe heart failure.

If you start at 60% ejection fraction, it is impossible to double it
to 120%. This is why Carl Foster said the most liberal estimate would
be from 60% to 80%. Note that this is a 33% increase and not a 60%-80%
increase as Catherine Bacon says below.

And of course, there is the increased a-v extraction noted by previous
answers.

So, to keep it simple, the increase in VO2max comes partly from an
increase in cardiac output (which comes because of a mix of an
increase in stroke volume and HR), and an and partly from an increase
in a-v extraction.


Of course, we don't usually exercise at VO2max so the changes with
exercise may be very different when exercising at VO2 max vs
submaximal exercise. I went looking for a table at VO2max but couldn't
get one online. Here is a table from a paper in JAP in 2009 in middle-
aged men cycling at 60-65% of VO2max. Note that most of the increase
in stroke volume does come from ejection fraction in this table, and
cardiac output increases are therefore due to HR and "ejection-
fraction related increases in stroke volume". At very high heart rates
experienced at VO2max, there is less time for the heart to fill, end-
systolic volume therefore decreases, and this leads to decreases in
stroke volume (not sure if ejection fraction declines but I think so).

Ian Shrier MD, PhD, Dip Sport Med, FACSM
Associate Professor, Dep't of Fam Med, McGill University
Past-President, Canadian Academy of Sport Medicine
Check out: www.casm-acms.org
SKYPE name: ian.shrier

Centre for Clinical Epidemiology and Community Studies
SMBD-Jewish General Hospital
3755 Cote Ste-Catherine Rd
Montreal, Qc H3T 1E2
Tel: 514-340-7563
Fax: 514-340-7564





On 1-Mar-09, at 12:36 AM, Catherine Bacon wrote:

> Alright. How does Lance Armstrong manage to increase his oxygen
> consumption by around 20 fold from rest to maximal exercise, when his
> cardiac output only increases by a factor of 10? I'm guessing that he
> must also have a substantial increase in his oxygen extraction (a-vO2
> diff) in addition to the increase in cardiac output. Does this answer
> Hansel de Sousa's original question? (or am I missing something).
> [Hansel, I hope that this was not a laboratory question for your
> undergraduate studies that you were supposed to figure out for
> yourself].
>
> Let's recap on the assumptions.
>
> His resting VO2 is under 300mL/min.
> (This seems reasonable for a 74kg (Wikipedia) athlete with minimal
> body fat).
>
> His max VO2 is 6000mL/min (6L/min)
> His resting HR is ?? - let's say 35 /min - Can it be lower than that?
> He's 37, but let's say 30 a few years ago when he was at his peak - so
> we'll assume that his maximal heart-rate is 190 / min.
>
>
> So, his HR increases 5.4x from rest to max.
> His left ventricular ejection fraction increases also. Carl Foster has
> cited some unreferenced data suggesting a liberal increase might be
> 60-80% - but since Lance is truely elite - lets say his lv ejection
> fraction (and therefore his stroke volume) doubles.
>
>
> Cardiac Output = Heart Rate x Stroke Volume
> so his Cardiac Output should therefore increase 5.4 x 2 = 10.8 x from
> rest to maximum.
>
>
> Because:
> VO2 = Cardiac Output x avO2 difference (Fick's principle)
>
>
> This would suggest to me that Lance's increase in Cardiac Output (from
> rest to maximal exercise) explains just over half of the increase in
> his
> VO2. The difference in the arterial to venous oxygen content of the
> blood must increase by a similar margin (just short of doubling).
>
>
>
> ------------------------------------
>
> Post messages to sportscience@yahoogroups.com. To (un)subscribe,
> send any message to sportscience-(un)subscribe@yahoogroups.com. View
> all messages at http://groups.yahoo.com/group/sportscience/.Yahoo!
> Groups Links
>
>
>