Weird result from heart rate drift test (w/ chest strap hr monitor)

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  • #42398
    Farley
    Participant

    I just got back from my second attempt trying to pinpoint my aerobic threshold via the heart rate drift test. My first attempt 2 weeks ago resulted in a 1.5% heart rate drift, so I tried again at a faster heart rate today.

    I ran to a quarter mile flat loop that’s about a half mile from my place, did the hour long workout and ran back. While I wasn’t always right at my target heart rate, I stayed within a few bpm on either side the whole time. The result I got was -0.5%, somehow at a faster pace my results are showing a lower heart rate drift.

    My first thought was faulty data, but everything looks fine to my eye. My GPS didn’t act up and ping me somewhere I wasn’t and my heart rate as recorded by my chest strap monitor looks like it has a normal fluctuation, although I am new at using heart rate data. My next thought is that I conducted the test wrong. I tried to control everything I could; I ran in the morning so the temperature change wouldn’t be significant, I ran a small flat loop, I ran to the workout and started straight away so my heart rate would already be stable. In re-reading the instructions I picked up on this line:

    “when you are operating in Zones 1 and 2 (intensities at which your aerobic metabolism is providing the bulk of the energy needed), your heart rate increases in lockstep with your pace if your movement economy is uniform throughout these lower speeds”

    At the beginning of the workout I had a hard time getting my headphones to stay in, so I was reaching up to fix them a lot. Could that have affected my movement economy enough to nullify the results? Does anyone have any other ideas? I’m going to try the test again at a higher hr, but if I’m doing something wrong I’d like to figure that out first.

  • Moderator
    Scott Semple on #42406

    Rather than a test at a higher HR, try a couple of tests at lower HRs first. I’m wondering if you’ve been testing near your anaerobic threshold rather than your aerobic.

    * At the aerobic threshold, HR could rise but doesn’t.
    * At the anaerobic threshold, HR doesn’t rise because it can’t.

    Take the HR from your most recent test and multiply it by 80%. Then do a drift test at that HR. Be aware that it will feel super easy. That doesn’t mean it’s wrong.

    Let the drift at 80% inform future tests. If it’s more than 5%, try something slower. If it’s less than 5%, try something faster.

    Participant
    Farley on #42409

    Thanks for the insight Scott. The first test that resulted in 1.5% drift was at 132bpm, and the second test I did today was at 145bpm. Given that I’ve got a thru hiking background with ~5,000 aerobically easy miles in the past couple years, and I can easily nose breathe at these paces, do you still think I should test again at 80%, or 116 bpm?

    Moderator
    Scott Semple on #42411

    It can’t hurt. The worst case is that you get another hour in at the most important intensity: Zone 1-derful.

    Participant
    Farley on #42412

    Beautiful, thank you!

    Participant
    OwenFW on #42414

    Farley, it was unclear to me reading this whether or not you are maintaining a constant pace throughout the workout. It sounded like you are maintaining a constant heart rate. I’m pretty sure the math of the pa:hr function wants a steady-state effort, i.e. constant pace (or power for pw:hr). Not quite sure how measuring a change in pace while maintaining a steady HR would mess with the results.

    Participant
    Justanotherclimber on #42433

    OwenFW, I was under the impression that a constant pace wasn’t what you were striving for but maintaining your heart rate close to your initial heart rate number. In which case your pace may go slightly up and down?

    Moderator
    Scott Semple on #42437

    If the terrain is flat and your pace or heart rate is relatively constant, then it should be possible to figure out the drift of the other.

    For example, if your pace is constant, then heart rate will rise, and you can figure out the increasing drift in heart rate.

    If heart rate is (relatively) constant, then pace will slow, and you can figure out the decreasing drift in pace.

    Participant
    OwenFW on #42440

    From the test instructions: “Hold that pace for an hour or so and notice if your heart rate begins to climb.” While Scott is right that the math of comparing the ratios will still work if you measure decrease of pace rather than increase of HR, you will be getting less data: you will only get your AeT and not the associated pace. While this isn’t as big a loss as not knowing your anaerobic threshold pace, which TP uses for calculating rTSS, it leaves you with one less piece of data for planning runs and races. How far will you get in one hour of running at AeT? If you do your test with a steady pace, you’ll know the answer to that question.

    The steady pace version of the test is also likely to return more logical results, since *any* starting HR chosen with your steady HR procedure is likely to yield extremely low pa:hr numbers since you may spend no time during the test above AeT, where nonlinear change would start. You could be within one beat of AeT and see next to no drift downward since it would all be linear drift. In the normal steady pace test, you just have to start at or just under AeT, and then some of the 5% will come from nonlinear-increase time above AeT. You could even use a steady-pace test to suss out an AeT that is above where you started the test. Maybe after your warmup you settle on a pace that keeps you at 143 bpm and then find that during the test your increasing HR stabilizes again at 150 and then you end at 1hr with only 2% drift. You probably just discovered that 150 is the number you should have started with.

    Finally, it’s really hard to keep a constant HR, but a constant pace is dead simple, especially on a treadmill.

    I’m no coach, though, and only have my own results and logic to guide me, so I could be dead wrong!

    Moderator
    Scott Semple on #42461

    Agreed. A constant pace is definitely a better method if it’s possible.

    Participant
    Farley on #42570

    Thanks everyone, I was under the impression I had to maintain a constant heart rate for the test. Maintaining a constant pace will be much easier and hopefully will get me results that make a bit more sense to me.

    Participant
    Farley on #42843

    Update: I did another test today. Knowing my own fitness background in regards to low intensity vs high intensity volume, I thought it unlikely that a test at a significantly lower HR would bring me closer to finding an answer. So I did my test today at a faster pace (second test was 10:00/mile, this test was 9:30/mile) and I believe I’m getting closer to finding my aerobic threshold. Here is the workout. PA:HR for the whole workout is 4.22%, and if you just select the last hour eliminating the first bit while my HR stabilizes it’s 3.29%. Are these numbers close enough to 5% to set my Zone 2 upper limit at 161 or should I wait until I get a result even closer?

    Moderator
    Scott Semple on #42847

    I think that’s close enough. I would use 160.

    As a double-check, have you done an anaerobic threshold test? Going as hard as you can sustain for 30′ (after a thorough warm-up)?

    Sometimes people go too hard when testing for the aerobic threshold and inadvertently find their anaerobic.

    Moderator
    Participant
    Farley on #42853

    I haven’t done the anaerobic test yet, I’ll do that as my next workout in a couple days. Thanks for your help Scott!

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