[kazGreg]

In the recent podcast episode #93 you took a question from Dave about his anaerobic threshold test.

Over the course of 1 hour his HR dropped from average of 177 BPM to 165 BPM, during which time he climbed over 800m.  You suggested that it was probably fatigue that slowed him down.

I wondered to what extent the increase in altitude was also the culprit.

I did an uphill trail race recently, climbing from 5200 to 10400 ft over 10 miles and just under 4 hours.   My average HR for the first few miles was around 160 and my HR for that last couple of miles was around 150.  I did slow down as well, in spite of similar RPE.

For reference I ran a road marathon a month later in 4 hours, with average HR of 152 BPM, with a Pa:Hr from TP of 6.3%, so I slowed down a little in the 2nd half and my average HR increased from 151 to 153 BPM.

I noticed a similar pattern to that in the trail race in my training runs at similar altitude.  As I get up to 10,000+ ft, what feels like the same RPE results in lower HR.  I’d have to kill myself to say get that 150 BPM up to the 160 that feels fairly comfortable at 5000 ft.

On the other hand, I know that if during that last few miles of that marathon I had tried to kick it in, my heart rate would have sky-rocketed, even though I felt far more fatigued than I did during that trail race. In fact my HR during the last  .4 miles was 162.

This suggests that anaerobic (or aerobic) threshold tests that involve significant altitude gain might be suspect.   Of course the 800 m in the case of the Dave question might not be enough to create this effect.
I suppose a related observation is that in the same way that one’s thresholds are different for hiking with a pack vs running, they’re different at 5000 ft vs 10000 ft.

You actually touched on this subject later in the podcast when you mentioned the HR data for the elite guys climbing Island Peak.

So there’s no pointed question here, but I’d be interested if you have any observations to make about this situation.  Thanks!

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