[Krizz]

Three months ago I determined my AeT using an outdoor test to be 157 bpm. Since I am starting a new training plan for mountain running, I tried to do an indoor test with a treadmill set to 2 deg incline wearing a chest-strap HR monitor. Since the treadmill is limited to 60 minutes, I warmed up on an indoor running track for 15 minutes, then used the first 5 minutes on the treadmill to get my HR back up to about 160 bpm and calculated the drift from minute 6 onwards using two halves of 27 minutes.

What stumped me was that twice my HR actually decline significantly, the first time just between the 13th and 16th minutes it went down to 142 and then later between the 52nd and 55th minute again down to 145. Apart from these two dips the HR seemed to hover around 160 going up and down 3 bpm. I left the incline and the speed constant.

However, when looking at the data of the two halves, I found no drift 🙁

The first half of 27 minutes measured from 06:00 till 33:00 gave HR of 158 bpm avg (min 132, max 166 bpm) whilst covering 4.24km at avg pace of 06:24 min/km (min 07:02, max 05:48 min/km). And the second half of 27 minutes from 33:00 till 59:00 gave an avg HR of 158 bpm (min 141, max 164 bpm) whilst covering 4.22km at avg pace of 06:23 min/km (min 07:04, max 05:51 min/km).

So I want to know: are those two three minute dips in HR a known phenomenon? I wanted to target 160 bpm but after initial stabilization for about three or so minutes it ended up lower. Should I redo the test or can I guestimate AeT for the purpose of setting zones with the data above?

Thanks for your patience with answering yet another HR drift test question!

[Scott Johnston]

Krizz:

The only explanation I can think of for a 15bpm drop in HR is some sort of glitch with the monitor.  Did your perceived exertion stay the same during those 3 minute periods as it did on the rest of the test.  It seems that even if you exclude those 3 minute drops in HR you would still get no or only a tiny amount of upward HR drift and perhaps the HR average would 160.

If you have been diligently training in Z2 for 3 months since that last outside test it is not at all unlikely that your AeT HR has moved more than 3bpm.  If I were you I would start using 165 as the top of Z2 for the next few weeks and then test again.

I hope this helps,

Scott

[Krizz]

Thank you for the advice! I adjusted zones the way you advised and will retest in a few weeks.

As you correctly guessed, since my previous test, I spent 6 weeks finishing a training plan for an event and spent a further 6 weeks in a transition period (as per TFTUA) where I trained in Zones 1 and 2 exclusively aiming to narrow the gap between AeT and AnT.

Yesterday on my longrun the HR monitor did it again effecting a mismatch between my breathing and the recorded HR, I had to stop, disconnect and reconnect it. Last week I neglected it in my gym bag – rookie mistake! So now I gave it a good clean and left it to dry properly, let’s see!

Thanks for taking the time to answer.

• This reply was modified 5 months, 1 week ago by Krizz.

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