Sometimes you can’t trust your heart (rate monitor)

Yesterday I went to the track in the morning to do some fast repeats. The scheduled called for 5 x 2:30 at 92% MHR with 1 minute rests. I ran a faster half mile to get my legs ready and proceeded to launch into the first repeat. I was running hard, breathing hard, but my HR was dawdling along at 86%. So I ran faster and harder, cutting the first repeat short at 1:44 when my lungs gave out. The HRM said I was at 88%.

Mystified, I ran my 1 minute jog and then tried again. Same thing. I jogged some more and thought about it. What was going on? Were my legs too tired to get myself going fast enough to get my HR up into the low 90%s? Was I glycogen depleted? Was the dreaded iron deficiency issue back? Why were my lungs giving out before my heart and legs?

I tried another and the same thing happened again. This was getting silly. Finally, on the fourth lap it occurred to me to look at my pace. I was running 6:18 pace. Aha. The HRM was bullshitting me again. Now I figured I’d been running these in the mid-90%s (which would explain why I was getting breathless before the 2+ minute mark). So I ran a few more quick ones and learned another lesson: don’t over rely on technology. I knew I was working hard and running fast. I should have trusted those perceptions over what the watch was telling me.

8 Responses

  1. There is the debate: HR v. pace. I go with the latter because (i) I still haven’t gotten around to getting a baseline for man (although I may try that at tomorrow’s 5K) and (ii) Daniels says HR can be variable on a day-to-day basis (DRF (II), at 61-62), as you found. I always like the precision, however misleading it might be, of focusing on lap times and the lines on the track. Of course there are days when, say, a 90 400 feels easy and others on which it feels impossible.

    • Something was definitely off technically, not just cardiologically (Hah! New horrible word!). I only wish I could run 6:18 at 88% but, alas, I’m not there (yet).

      It’s a good thing I’ve become less anal retentive about not only paces but also about HR readings, since I’ve gotten misled by both over time. Although I have to say that running by HR has gotten me pretty good at dialing into a certain effort if I run it often enough. Unfortunately, 92% is not one of those efforts.

      I hear you had a nice chat with Jonathan this morning. He never fails to comment on how fast you run on your easy lopes.

  2. I always thought that HR didn’t work for shorter intervals, because of the lagtime inherent to a) your HR adjusting to the heightened requirement for oxygen and b) the HR monitor’s lag in measuring HR.

    I dunno. I really RELY on my HR monitor only for keeping my easy runs easy. I monitor it during tempos, but just to make sure I’m not really overdoing it. For intervals, I generally find HR to be fun, but useless.

  3. Does the 310xt give a read-out of “current” ave HR? I’d say it’s next to impossible to run at an average of 90% for a 2 minute 30 second interval. After a minute’s rest your HR would be down to, say, about 65%. So at the start of each interval, you’re starting at 65%. Say you accelerate the HR up to 98% (quite possible), your average is only going to be around 85% because you spend the first 30 secs to a minute getting the HR up near 90%. Also, the fitter you are, the harder it’ll be to maintain a high average HR in short intervals because the starting (recovery) HR will be lower.

    For example, I ran some 500m intervals a couple of weeks back at 5 to 10k race pace with 1 min rests. The ave HR for them was 85%, yet I can average about 92% for a 10k race.

    Anyway, I agree with Joe in that it’s probably best to go with pace for short intervals. For 2000m intervals up, and time trials, ave HR would work OK.

    • Thanks for the astute comments, Ewen and Darkwave. I’ll note this in my next exchange with Coach Kevin. Notable since I have 1 minute intervals coming up.

  4. The short interval is key for Daniels short “intervals,” i.e., the theory is that it takes 3 minutes to get the heart into the VO2max zone. Thus if you run for under 3 minutes, you cheat by keeping recovery short so that when you start the baseline is already elevated and you needn’t run 3 minutes to get the benefit. I tend to do 1:20 break for a 2:40 run.

  5. […] Sometimes you can’t trust your heart (rate monitor) […]

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