Ridecamp: Re: [RC] Born to Trot?

In mammals energy expenditure is related to external work, just like a
machine.  Using a treadmill, speed and grade are increased to increase the
work (kg-meter/min) required to maintain pace with the treadmill.  As work
increases energy expenditure (calories) increases in a linear fashion.
That is the harder you work the more energy you consume.  Expired gas (air)
is collected and sampled through oxygen and carbon dioxide analyzers and
the rate of gas (air) expired is measured with a device that is like a
turbine with a speed sensor (pneumotachomter).  From the flow rate and % of
oxygen and carbon dioxide expired we know the total liters of oxygen
consumed by the animal.  Each liter of oxygen consumed yields between 4.7
and 5.05 calories/liter of oxygen, the difference being the ratios of fat
(4.7 kcals/liter of oxygen) and carbohydrate (5.05 kcals/liter: no thats
not a typo, there is more energy per UNIT oxygen in carbohydrate than fat,
BUT more energy per unit stored in fat than carbohydrate by a factor of
more than 2).  The relative use of these 2 fuels is also taken into account
in calculating energy expenditure.

Heart rate is fairly linear in laboratory conditions to oxygen consumption,
but therein lies the folly of using absolutes for heart rate.  In endurance
horses, even at a slow trot, exercising for hours on end, heat storage
causes heart rate to drift and messes with this linear relationship between
heart rate and energy consumption.  For all the energy used to propel the
horse forward only about 30% is used for motion, the rest is released as
heat.  The longer and harder you work the more energy you "store" and must
release.  This is also the job of the cardiovascualr system which serves as
a water pump to circulate warm blood from the core to the skin (radiator)
for cooling.  So each horse's heart rate can vary considerably based upon
the fitness of the horse, terrain (which can increase work), and the
environment, such as ambient heat, humidity (God bless the
midwest.....ick!), and radiant heat. You simply can't compare the same
horses heart rate at a 10 mph trot on an 80 degree day in the desert to the
same horse on a 70 degree day w/80% humidity in stickly midwestern states.

Often times what is learned in the lab can seem wrong in the field.  What
you need to keep in mind is that in the lab variables you can't control as
a constant such as environment, speed, and grade can be kept fairly
constant.  The application of what is learned in the lab takes more than a
simple step.  Keep in mind also the limited time that can be employed in
exercising a relatively small number of horses (maybe 10?) in the lab,
usually not more than 90 minutes on a treadmill.  In competition riders
vary pace to allow for recovery such that riding an event is actually
intermittent in nature, not the constant velocity normally employed in the
lab to limit the number of variables.  IN fact one flaw in applying the
constant speed mentality of studying amimals during exercise is that most
animals in the wild use locomotion intermittently as they hunt, forage,
flee, rest, mate, etc.

The general public often find lab results limiting, but speaking from
expereince in testing & training rats, horses, and humans, it is extremely
painstaking in order to be accurate and this type of basic research is
merely a foundation to build upon in the field.  A 20 beat difference
between an extended trot and a canter is no blip, that is significant!

Of further interest might be the unique giats of other breeds that choose
pacing, or the unique gaits characterisitic of walking horses, paso finos,
rocky mtn horses, etc......


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