Threshold vs Lower Threshold

What do these represent physiologically? I assume Threshold is defined as that point otherwise known as one hour power but also wonder if it is that point that might be known as Lactate Threshold, which to me is more meaningful as it represents that point where aerobic effort tips into anaerobic effort. This is something I can almost sense as breathing rate increases to where I can’t sing. Lower threshold power I could not begin to define so please help me with that. I was riding on feel alone for decades before getting a power meter and learning all this lingo. An academically trained scientist I understand the biology/physiology. I like having numbers to use to meter my efforts, know where I am at and to challenge me to improve.

No, it’s below that - I think it’s generally about 80% of TP and you should be able to breathe normally, i.e. also your HR should not be too high.

In theory, you would be able to ride at that power for a long time, although obviously not indefinitely, which is not possible at LTHR…

“Also referred to as LTP , this represents a modeling artifact associated with the depletion of Endurance Energy. As endurance energy declines over the course of a long activity, slow-recovery / long-term fatigue takes hold and Threshold Power, High Intensity Energy and Peak Power decline. The affect of long-term fatigue manifests in reduced MPA and MPA that declines more rapidly. LTP represents the lowest possible value for Threshold Power when all Endurance Energy reserves have been depleted.”

Ok, I think I understand better how this software “XERT” is constructed.