<< Has anybody else noticed that the longer you get in the ride, the lower
and
more stable the HR becomes? I don't mean from the start when the horses are
excited, but say from the ten mile point to the forty mile point? It's like
they settle in - does this happen to horses on a 100 miler? (I'm dying to
find out myself). >>
Two factors at play here: expanded blood volume and splenic contraction. As
the horse gets well into hard work, the blood volume expands while about 50%
of his red cells are injected from the spleen into the bloodstream--greatly
increasing his oxygen delivery capacity. With this "backpack of endurance"
working for him, his demand on the "pump" drops off somewhat. With our horses
doing interval training, the second heat, which is always faster, generally
produces a lower heartrate--for the same reason.
ti