Home Current News News Archive Shop/Advertise Ridecamp Classified Events Learn/AERC
Endurance.Net Home Ridecamp Archives
ridecamp@endurance.net
[Archives Index]   [Date Index]   [Thread Index]   [Author Index]   [Subject Index]

[RC] Resting HR on young horses/Stroke Volume/Bradycardia - k s swigart

Beverly Kane said:


What I don't get is how the -unconditioned- resting heart
rate in horses is any predictor of cardiovascular fitness
for endurance.


I contend, that it isn't.  What a low unconditioned RHR in an endurance horse 
is good for is to make it so a horse can "recover" to an absolute criteria 
(which all endurance rides use because, as she mentions below, "time to recover 
to 110% of RHR" is impractical/impossible to implement at and endurance ride) 
with less fitness.


In humans, the recovery time to resting HR is a function of
conditioning, not of the absolute value of the RHR. Some 
humans with very low RHRs in the unconditioned state become
-dangerously- low in the conditioned state.


And I am a person who kinda falls into this category.  I have a horse with a 
higher RHR than mine. My "marginally conditioned" RHR (I have no clue as to 
what my unconditioned RHR would be, since I cannot recall, at any time in my 
life ever being completely "unconditioned" I may have been when I was 4 years 
old, but I'm pretty sure nobody was taking my HR then anyway) is about 48 bpm.  
If I start really conditioning myself so that I would describe myself as very 
fit (instead of just marginally fit) it drops down as low as 40.  I avoid 
conditioning myself to what I would describe as "super fit" because I can tell 
when my level of fitness is getting me to the point where I have trouble 
maintaining a high enough heart rate to keep my blood pressure high enough to 
keep from passing out any time I make a sudden move.

As I get fitter, it gets harder and harder for me to keep blood in my head :).  
Such that as I get fitter, what I have to do immediately post exercise is put 
my head between my knees to keep from passing out and falling over.  And this 
condition is exacerbated if my blood sugar has gotten a bit low.  As I get 
fitter, I have to make a concerted effort to do things to keep my heart rate 
elevated post exercise.


I don't get why low RHR is so desirable in the purchase
of an unconditioned horse. I would even be concerned that
such a bradycardia might be a sign of a pacemaker or
conduction (of electricity) disturbance.


This is the reason that I am violently opposed to any further lowering of the 
absolute criteria imposed at endurance rides (as was suggested some time back 
in one of Matthew McKay-Smiths proposals).  I am even of the opinion that in 
most situations 60 is probably too low.  What the imposition of lower and lower 
HR "criteria" at endurance rides has done is to select for horses that have 
borderline pathological bradycardia (and being somebody who can be described 
that way myself, I have at least one rat's worth of experience to base this 
opinion on).  

It wouldn't surprise me in the least if some of the rather surprising (because 
the horse was totally within all veterinary criteria throughout the day at the 
vet checks) "crashes" we see at endurance rides are because many of the horses 
we see at endurance rides have pathologically low heart rates, so they don't 
keep the blood running around in their bodies fast enough to actually be able 
to recover from the effort.  And it wouldn't surprise me in the least if we 
start seeing more of these types of crashes now that lower "recovery" criteria 
have become widespread.

I am perfectly content with my horse with a RHR of 52; she's a great horse. She 
is even a great endurance horse.  The others that I have have much lower RHRs, 
and I constantly remind myself not to be deceived into thinking that their good 
"recoveries" (i.e. to 60) have anything to do with their level of fitness.

kat
Orange County, Calif.
Somebody who, when she was in college and participating in college athletics 
(so an intense conditioning program) was treated for low blood pressure which 
was mostly a function of bradycardia.  These days, I just make sure I don't get 
too fit :).


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Ridecamp is a service of Endurance Net, http://www.endurance.net.
Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp
Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp

Ride Long and Ride Safe!!

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=