Friday, February 19, 2010

Heart Rate Madness

As a devoted Garmin-ite for two years or so, I have learned to take the heart rate output with a grain of salt. Heart rates vary day-to-day for reasons that are both known and unknown. Things that affect heart rate during a workout include ambient temperature; time of day; sleep; caffeine intake; weight; pace; state of hungover-ness and general workout fatigue, i.e., if you workout three straight days, heart rate will be higher on third day; it will also be lower after a rest day.

With all that, I have learned to accept variations (plus or minus 5 heart beats per minute) in heart rates during training without freaking out. Of course, I love it when I have a workout that shows a strong pace and a surprisingly low heart rate. I immediately chalk that up to my improving training and fitness level. And a bad day I chalk up to the vagaries of the heart rate gods. But now and then a workout will come along that you just have to say is an aberration and move on without trying to figure it out.

On Monday February 15 (after a two day break, but with a twinge of hangover from Valentine's Day), I ran in my gym at about 5 p.m. I ran 6.2 miles at 8:27 pace. My heart rate was pleasantly low: in the 140's with a high of 145. I ended with the feeling that I had just had a GREAT workout.

Yesterday, I ran in the same gym, at the same time, at the same pace, on the same treadmill. No alcohol remnants in my system, and after a day on which I had not run (although I did a weight workout that left me sore). heart rate -- high 150's, with a top of 164. On average, about 10% higher than 3 days earlier. I was stunned; I actually had planned to run faster, but held back because of my high heart rate.

For heart rate purists, this is a dramatic difference. A 75% heart rate workout is easy; an 85% is approaching lactate threshold or tempo run pace, and carefully managed. Through the genius of SportTracks, here is a graphic comparison of the two workouts:*

So what do I make of all this? Not much, actually. A vivid demonstration of the reason not to take any one workout or data point too seriously. And, evidence of the reason not to focus on the heart rate to the exclusion of all other things, such as how I feel on a run.

*Also note the spike in heart rate at the beginning of the Feb 15 workout. My heart rate usually spikes in first 5 minutes or so, even if I warm up. Without the spike, the difference would be even more dramatic. Also note the effect on my heart rate on the red line when I had to stop and tie my shoe.


  1. i need a new HR strap. i havent been wearing the watch since before marathon for that reason and also because i learned how to 'gauge' without..

    but now its about to be warmer and here in Houston, i feel better with that HR gauge...

    Junie B

  2. This is exactly why I don't use a HR monitor. Too much info, and frankly, I think knowing my HR all the time would freak me out a bit. I know whether I am working hard or not. I can listen to my breathing, etc. Also, I don't have any family history of heart issues, so for me, it's the Garmin without the HR strap!

  3. I am totally interested in my HR right now, I have no idea why. I've been taking it on hill runs and tempo runs. It bugs me that it isn't accurate and may vary depending on the things you mentioned. I need to look at my work outs this week and try to check out SportTracks. Thanks for the info.

  4. Hi NY Wolve,
    I am a pretty new runner so I really havn't been paying attention to my heart rate like you. I do have a Garmin with the heart rate attachment but have not used it yet. I should really take a closer look at it and see how I can used it to help me train:) Have a good weekend!!

  5. This post was interesting, because I am not a technical runner at all, I just go until I can't go anymore. I'm actually in the market for a Garmin, so I'm sure I'll get all techy once I do so....

  6. I'm a new runner-as in I started last month-and I use my Garmin HRM religiously. I haven't noticed any variances on HR, but the elevation/speed can be way off. This post is a good reminder to me to take all things into consideration. Thanks.

  7. My husband is training for a marathon. He also just mentioned the other day that he loved his Garmin (a gift from me.) We live at 6500 ft so I'm thinking anything he runs at sea level should be a piece of cake.

  8. I agree that you have to look at heart rate with a grain of salt. I do love using it though and have been for about 5 years. Looking back at my training data it helped me figure out that I was running my LSD runs too fast for me. Maybe your lesson is that you should have a little too much to drink before you run? Just kidding... :)

  9. Maybe your result of the 15th February is the proof of the power of love... ;-)

    Without kidding, maybe you where just in a very positive state of mind!

  10. If you tighten the strap on your heart rate monitor and wet the contacts before you put it on, you won't have the problem with an initial spike in readings. If you don't wet the contacts, it takes a few minutes of running for you to sweat enough for it to work properly.


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