Peter Attia's lactate was 1.5 after a Zone 2 ride where he prioritized RPE over predicted heart rate.

“my predicted heart rate for Zone 2 was 128 beats per minute uh which is low for me so I get on the bike and I start riding expecting to feel horrible by the way and I don't I feel really good — so I blow past 128 — I'm into the mid 130s I'm feeling great I just keep pushing the power because again that's that's what's driving my heart rate is how many watts am I am I increasing so I'm I'm increasing wattage I'm increasing wattage I'm increasing wattage and then finally at about a heart rate of 144 I feel like I'm in the right spot”

“any of the uh data you would use to predict heart rate on me would say 144 is too high because 180 minus my age puts me in the well it actually puts me at 128 — um so that's clearly wrong even if you adjust up and add 10 for being very fit which would be maiton adjustment that still puts me at 138 and oftentimes I am in the 140s at my zone 2”

“sure enough at the end of that ride my lactate was 1.5 in other words I probably still had a little bit I could have done but 1.5 is not not not not bad I try to be between 1.6 and 1.9”