Am I doing this right?

December 3, 2012 11:09 AM

I bought a Timex heartrate monitor and input all the data. Now when I exercise I am having a hard time staying in fat burning zone or any zone. Seems my heartrate swings wildly from 80-135 during my routine. I am doing a combo of isometric and yoga exercising and am trying to keep it in the fat burning zone.

If I go over I slow down to bring it down but then sometimes when I am working it seems to drop below 100.
Is my monitor defective or am I just not doing a good job of keeping a steady pace?
I am older and overweight but have done exercises off and on for many years. Also did a marathon 12 years ago.

posted by shaarog to health & fitness (8 answers total)

Heartrate monitors tend to be especially prone to error and lag if the detector isn't damp. If you're trying to keep your heartrate relatively low, you may be not keeping the monitor detector damp enough to be truly accurate. I would start with a dampened back of the band near the detector. Then just try to keep a steady pace, and if you don't feel like your heart rate has really skyrocketed or plummeted, give it a few minutes to recalibrate before changing your pace.

After you've done it for awhile you definitely get a better sense for your own body, and when your HRM isn't accurate.
posted by ldthomps at 11:34 AM on December 3, 2012

Are these swings happening as you are maintaining the same level of exertion? Or does your rate go up when you are moving/lifting more/faster? If the former, then maybe your monitor is being flaky -- where do you wear the monitor? does it go around your chest? You might have to adjust where you're putting it, or sometimes getting the electrodes wet first will help with the detection. What happens when you take an old fashioned pulse reading (fingers on wrist, look at clock)?

If the rate is fluctuating with your work level, then it's probably doing the right thing.

How are you calculating your "fat burning zone"? If it's just some percentage of 220 minus age, then you're using what is at best a generalized approximation and not what is optimal to you.

The idea of a "fat burning zone", is that it's a zone of intensity that you can maintain for an indefinite period of time that still provides some amount of caloric benefit. If the top of your FBZ is 140, and you can maintain 150 for 45 mins of jogging, then staying at 150 is fine, for you.
posted by sparklemotion at 11:35 AM on December 3, 2012

I think it's not worth worrying about the so-called fat-burning zone. In the "fat-burning zone," your body burns fat as a higher percentage of total fuel. But working out at a higher intensity burns so many more calories in total that you burn more fat anyway (even though it is a lower percentage of total fuel burned). So I would say to err on the side of higher intensity, so long as that's safe. I don't have any advice about the wide range of fluctuations, though.
posted by stopgap at 11:36 AM on December 3, 2012 [1 favorite]

Sometime when you're feeling the burn and you notice the monitor is reading very low, pause and take your pulse manually for a few seconds - you don't have to be super-accurate, just enough to confirm whether it's really 80bpm or more like 130.

If the machine is having a hard time getting a reading it can easily skip beats; sometimes the wacko readers on the handles of gym equipment read my pulse as half-counts (75 instead of 150), but I'd hope that a stand-alone monitor wasn't so flaky.
posted by aimedwander at 11:50 AM on December 3, 2012

Thanks Stopgap. Very interesting.
Sparklemotion - I used the booklet that came with the monitor (did 2 separate activities and averaged the rate etc) so I think I got the rates right. I am wearing a chest strap that I wet before putting on and a watch on my arm. I cannot tell how hard I am working really since the isometrics jack up my heartrate without the usual running/moving.
Guess time will tell if it is working to pull the weight off.

Thanks for the great feedback.
posted by shaarog at 11:53 AM on December 3, 2012

Aside from agreeing with stopgap's skepticism about the "fat-burning zone", I would also guess that isometric/yogic routines generally do not result in a stable heart-rate. The poses, movements, etc are irregular and involve varying degrees of effort.

HRMs are most useful for steady-state activities such as cycling or running.
posted by wutangclan at 12:48 PM on December 3, 2012

I had a Timex before I bought my Garmin, and the Timex sucked ass. I think you might just have a crappy monitor.
posted by peep at 2:06 PM on December 3, 2012

If you could pinpoint the exercises that your heart rate is dropping during, we could probably offer some feedback about how to modify them to increase your exertion level.

For example if your isometric exercises involve free weights, you could increase the weight. If it was a specific yoga pose, let's say downwards dog, maybe you're holding the downwards dog (a "rest" position) for too long and you could try to accelerate your pace through your series of poses.

You really should be able to tell if you are working hard regardless of whether you are moving around a lot. For example, during a yoga routine, if I'm lying in child's pose, I know I'm not exerting myself because my breathing is even, I feel rested, none of my muscles feel under any strain. Contrast that with a pose I find difficult, like crow pose - when I'm doing that, my muscles are burning and straining to hold the position, and I feel like I am putting in a ton of effort to hold the pose as long as I can. Neither pose involves any movement, but one is much more challenging.
posted by treehorn+bunny at 4:55 PM on December 3, 2012