Training Question.

I am riding my bike on the trainer in what’s supposed to be a tempo zone. My heart rate is well within my Zone 2 Aerobic Zone (based off Heart Rate Reserve and got my max with a max HR test). My breathing is slow and controlled. Talk test validated, I was talking to my wife and kids throughout. My legs were killing me though, the effort felt very hard on my lower body. I was even borderline cramps in my upper quad and calves at different points.

Some more stats: My cadence averaged 90 RPM for the ride, it was only an hour long including warm up and cool down, just 45 minutes of work.

According to my internal markings I was well within my limits, but on race day I would never hold that power given how my legs felt.

What’s going on? Where is my training deficit?