Heart Rate and Exertion

August 11, 2004

A friend is complaining because her heart rate monitor is telling her that she is not getting nearly as much exercise as she thought she was getting.

Erm, let me share a deep dark secret with you.

Measuring exertion by heart rate is a loose approximation unless you have TWO crucial data points to work with: resting heart rate and maximum exertion heart rate. You know the first, and with that you can estimate exercise ranges. The only way to find the second is to test for it - and if you have a weak heart the test might test to destruction. So check with doctor before trying this one.

Basically, wearing the monitory, run 800 meters hard, rest 20 seconds, then run 800 meters full out as hard as you possibly can. That should spike your heart rate to its maximum.

Of course, if you can't run hard for twice around a track, you can't use this test. There are other variations, usually involving a treadmill and a doctor's office. For most of us, we don't need it. We can use the 3 basic tests.

Light: you can sing
Moderate: you can hold a conversation
Hard: you can speak a few words but not converse

Those are as accurate and perhaps more useful than any heart rate monitor in the absence of a full data set.

If you still want the monitor, check to see if it is estimating ranges using the ballpark measure or using the formula that accounts for increase over resting heart rate. The latter is more useful for folks with low resting heartrates. 54 is a pretty good resting heart rate. I think it is lower than mine these days.

Posted by Red Ted at August 11, 2004 07:52 AM | TrackBack

I've been meaning to make a comment in this entry. Better late than never, I guess. :)

I'm unsure how the HR Monitor estimates ranges. It asked me for my age, height, weight, and DOB. Somehow, using those numbers, it came up with a formula.

When I took the HR Monitor to Cycling class, it said I'd burned 401 calories. When I entered 60 minutes of "Bike, Stationary, 150 Watts" into BalanceLog the next day, it said 450. The 10% variance made me cranky -- 10% over a week's worth of activity becomes significant.

However, when I changed the 60 minutes to 55 minutes, and accounted for the 5 minutes of "Cool Down & Stretching" we do at cycling class, it gave me 413 calories, which is close enough. The lesson learned became: "Don't cheat on minutes when entering activity into BalanceLog."

In any case, thanks. I'm glad you're around to be my Voice of Reason.

Posted by: KJ at August 15, 2004 02:21 AM

I have no idea how useful heart rate monitors are for counting calories.

They can be very useful for generating a training effect.
Basically, exercise below about 50% of your max heart rate will burn calories but will do little to improve your ability to exercise in the future.

There are also aerobic and anaerobic threshholds. The first is the point where you generate a training effect, usually 55% to 60% of max. That corresponds to the point where you stop singing but can still converse.

The anaerobic threshold marks the point where your body consumes more oxygen than it brings in, and has to shift to the short-term stores of chemical energy in the cells. If you train _just_ at that point - where you can no longer really talk because you are breathing too hard - you increase your ability to take in oxygen. Other forms of training, anaerobic training, can increase the stored chemical energy in the muscles.

As an aside, the reason the 400 meter is such a nasty race is that it is run anaerobically, and the human body normally stores only enough energy to run about 300 meters. To get through that final 100 meters without "hitting the wall" you have to train your body extensively - and even then you can seize up and stop running.

Posted by: Ted K at August 16, 2004 10:14 AM

"I have no idea how useful heart rate monitors are for counting calories."

Somebody, somewhere, must've figured out a pretty decent formula. Cause the HR monitor matches BalanceLog pretty closely (and showed me that the HMR numbers are just plain wrong).

Posted by: KJ. at August 16, 2004 04:01 PM
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