Susan:
<< Some research has said
that a HR of 150-160 bpm will indicate the anaerobic threshold has been
reached and that only the amount of work (ie, the running speed,
etc.) required to reach that HR will change (increase) as the result of
conditioning. >>
In one of my early books I used that number, too. but that number is derived
from the human literature (max heartrate in humans is about 200 BPM) and does
not apply to the horse. Some horses may reach LA4 at this heartrate, but I've
never seen it happen. Another thing to know is that heartrate is not a direct
reflection of LA status--you have to sustain anaerobic work for a while
before climbing above 4 mmol. In endurance horses, I just can't imagine a
circumstance where racehorse-level lactates are reached. Remember, LA4 is no
problem for any horse.
Another thing about LA fatigue in horses vs humans: one of the problems with
high lactates in humans is that they inhibit oxygen release from red blood
cells. this does not happen in horses.
ti