Re: Heartrate Threshold

[CMKSAGEHIL <CMKSAGEHIL@aol.com>]

Maybe I have missed it in this thread, but the bottom line about heartrate
thresholds is that the threshold is the point at which the heart can no longer
refill properly between strokes, hence the stroke volume goes down, hence the
cardiac output actually decreases.  As someone pointed out, the next step up
is fibrillation...

Mammalian heart rate correlates to body size, hence a mouse has a very fast
rate, an elephant has a very slow rate, and creatures in between have
appropriately in between heart rates.  The thing that makes the horse truly
unique is that he is the ONLY species, apparently, that can raise his resting
heart rate to over 6 times his resting rate!  In all other species, the
threshold is 3-4 times the resting rate.  So a mouse with a norm of 200 can go
to 600-800, an elephant with a norm of 22 can go to 66-88 or thereabouts, but
a horse with a norm of 40 or less can peak out at 240.  Just one more of the
truly amazing adaptations that makes the horse the athlete that he is...

Heidi