Heart Rates and Lactate Threshhold

I am aware of the concept of LT or AT. Some claim it can be found
using the Conconni protocol. Others use lactate measurements.

Out of these sorts of tests one receives advice - this is the heart
rate you can maintain for about 1 hour (it can be expressed in terms
of wattage, I believe). The test was accurate for me: I had as an
average heartbeat the LT heartbeat for 72 minutes.

Question: if one is riding longer events (50 miles, 100 miles etc),
what heartbeat can be maintained for periods of 2 hours or 3 or 4
hours? Are they expressed as percantages of the LT heartbeat?
.

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