Judd is very good at his job!
Treadmill running paces do not correlate well to running outside.
I went to see Judd at UC Davis this morning for the metabolic efficiency and lactate test. This is the “slow build” test. Not seeking VO2max. Just the first ventilatory threshold and endurance-pace training zones. And substrate utilization.
After a 20 minute self-selected warmup, the test was started at ~13:20 min/mile pace (walking). Every 4 minutes, a lactate test and increase speed 0.5mph. I walked the first two intervals and then started running. Stopped after 4 minutes at 7:30 pace. Which is about as fast as I ever run doing intervals.
Computed first ventilatory threshold (first lactate lift above 1mmol) at 142bpm and 9:19 pace. That is consistent with what I feel running. That’s the level at which I feel I’m starting to work just a little instead of simply cruising.
At baseline lactate, plus 1mmol, I was at 148 HR and 8:42 pace. Last time I did an AeT test per this site, I held ~148HR for an hour, but was at around 9:10-15 pace. So perhaps I’ve gotten more fit. In Judd’s methodology, this is top of Zn2, same as Scott, et. al. Again, consistent with my experience.
In practice, I do most long miles at around 132-135 HR. I will pick it up to 142-145 in the second half of a long run. If it’s hot out, it will drift up there on its own after a couple hours.
Judd put my Z1 range at under 141. He calls it “slow endurance.” With pace slower than 9:22. Which I do. Again, this is consistent with my experience.
Z2, or “long endurance” for me would be 141-148. In an ultra, I’ll never be in that range other than on a short-ish hiking climb. Pace in the 9:22 – 8:42 range. A place I don’t really go.
Z3 would be above 151 HR and faster than 8:30. Interval stuff for me.
On energy utilization, my fat/carb crossover point is at 148 HR; 8:42 pace. Faster than I thought. I’ll never run that hard in an ultra; that’s marathon pace. At 100 mile race-goal type paces (early flat miles slower than 11’s; averaging slower than 12-13’s with walk breaks, etc.) I am burning 65-70% fat. Only 185 – 200 carb calories an hour. This is good news for fueling strategy.
My max fat rate of only 0.83g/min is a little low. He said it’s good for a trained runner, but could be a lot higher with specific fat adaptation strategies. But I don’t think I need to go there. That max fat burn rate comes at 9:14 pace, and I won’t be going anywhere near that fast.
I did this mainly out of curiosity. I am happy that the results match what I’m feeling, and what they folks on this site have been saying.