heart rate and threshold

["Beth Glace" <lb@nismat.org>]

In response to the question regarding the heart rate at the anaerobic 
threshold:  There is lot of variation between individuals  in heart 
rate, and generally heart rate at anaerobic threshold will vary 
similarly.  So if the max heart rate is higher than average in a 
particular animal so would be the heart rate at anaerobic threshold. 
If you are using a heart rate monitor to train yourself or your horse 
it is important to know, at the very least, what the max heart rate 
is.  Otherwise you run the risk of overtraining or undertraining,  
all in an effort to be scientific.  Make sure to observe and use 
common sense in addition to the monitors!   Although max heart rate 
in humans is typically calculated as 220 - age, I have seen 35 year 
olds with max rates of 215.  They are totally normal and healthy, 
they just need to exercise at a higher than expected rate. 
Additionally,  as an animal heats up OR dehydrates 
heart rate at a given workload will increase.  Blood is pulled away 
from the central circulation when it is brought to the skin for 
cooling, and the heart has to beat more rapidly to circulate the same 
amount each minute.  So, you may notice that heart rate drifts 
upwards in the heat.

 Beth