HR's up to 220, etc.

["Whitney Bass" <bass@bigsky.net>]

I was just reading "Advances in Equine Nutrition" (edited by J.D Pagan, and
put out by the Kentucky Equine Research, Inc.), and came upon some
interesting and relevant info.  The kind that is relatively basic, but is
nice to "brush up on" -- thought you all might like to see some of it too.

  "Cardiac output (CO) is a measure of how much blood the heart can pump
per minute.  CO is the product of heart rate (HR) x stroke volume (SV). . .
Horses have maximal HRs of 220-250 bpm.   SV is around 0.8 -- 1.2 liters
per beat.  Therefore, at maximal exercise, CO can reach over 250 liters per
minute.  This is comparable to pumping a 55 gallon drum of blood through
the heart each minute!  This massive CO is one reason that horses are such
good natural athletes.
    As a horse becomes more fit, SV tends to increase and HR at a
particular speed decreases.  Measuring the speed at which a horse can
exercise at a specific HR (i.e., 180 or 200) gives a good indication of its
relative fitness."