my advice wrote:
In races you can come close to max in the final sprint, but only if you are relatively fresh. My max Hr was reached in an interval training. Intervals of 400m, not very hard, but the last one all out.
A 5k race is a good test, *IF* you're fresh enough to kick in hard the last quarter mile. You might hit MHR at or a few seconds after the finish.
Example: My MHR was determined to be 190 by a test at the performance lab at UC-Davis. I could hit 189-191 by running a 5k holding back enough to kick in the last quarter mile. If I raced so hard that I couldn't forcefully kick in from 400m out, then I couldn't reach MHR. In those cases, it would top out at 184-185.
MHR isn't a very useful number. The HR you can maintain in a one hour time trial (Lactate Threshold... is this the right term?) is more important.
LT is the upper range of your tempo pace zone. The lower range is roughly 10% lower. For example, when my MHR was 190-191, my LT HR was 171-173. Once I went over 173, my HR would gradually climb until I was forced to slow down. On tempo runs, I'd run hard until I hit 171 and then maintain that HR.
Your HR can tell you if you're running your easy runs too hard or if you are overtrained. You don't need to know MHR for either of these purposes.