Heart rate watch question

The heart rate sounds about right for the type of workout. The 850 cal does not sound right. When I run, I burn about 100 calories per mile. You could test out your watch, with settings entered, by walking a mile or something, then, lookup the exercise on this site and see what the suggested calorie burn is.

I have a Garmin 405CX and it's accuracy is good b/c it has GPS and heart rate monitor. I use a footpod when indoors. It also requires gender/age.

What are you doubting the heart-rate monitored or the calculated burned calories?

The first one should be pretty accurate. But I would doubt the last one, the burned calories.
There are a few calculation algorithms, but they all include your height, weight, age, gender as static and pre-set variables and the meassured heart rate, aswell as the training duration and – if you have a good HRM – even these splitted up in intervalls as variables.

This is the most accurate way to calculate the burned calories, which are indeed nothing more than the power (e.g. Watts) you put as effort into your training.


Have look in the manual and make sure that there really is now option to enter your height and weight etc. If so, bring it back...it will always provide error-prone results.

Totally agree. If you can't input height/weight, it is really no more accurate in calculating calories than MFP.

I know my calorie burn numbers changed dramatically when I re-entered my lower weight into my HRM so I think maybe its just an average for a 150lb person (as most assumed averages are). I doubt its accuracy.

Sorry, I should correct that. I think my calories burned are too high. My heart rate is about what I thought it would be.
I have adjusted the age and gender. I will give it another go and see what it says. Maybe that will change things? I know it is better to be able to enter height and weight as well, I thought this one would but that is a different model. If I am not happy abfter a few more days, I will go exchange it.

I have been losing weight so very slowly(1/2 lb per week) and I am curious as to whether it is because I am not eating enough net calories because my calories burned are actually higher than what I enter.

I know 1/2 lb per week is nothing to sneeze it, I am proud of myself, but as I get closer to my goal(70lbs lost, I am at 54) it is getting tougher and I want to make sure I am not causing it to slow down.

Well, the more fit you become, coupled with weight loss, the less calories your body will burn, so it's normal for the body to start slowing down with losing weight as you get closer to your goal weight. What matters is how you feel overall right now. So far you've done a great job and you should enjoy that accomplishment. I fully embrace and celebrate the weight I'm at now, even though I've been shy of my goal weight for about a month now.

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Well, the more fit you become, coupled with weight loss, the less calories your body will burn, so it's normal for the body to start slowing down with losing weight as you get closer to your goal weight. What matters is how you feel overall right now. So far you've done a great job and you should enjoy that accomplishment. I fully embrace and celebrate the weight I'm at now, even though I've been shy of my goal weight for about a month now.

Sorry, but that is not true in general.

Basically it is all physics...
Calories get burned by using your muscles to create motion.

If you cycle uphill for 100m height and your weight alltogether (bodyweight + bike + clothes) 100kg and you do that in 10min. (=600s).
The power you will have to provide to climb that hill will be:
P = m*g*dh/t = 100kg * 9,81kg/s² * 100m/600s = 163,5W

But you will need to work harder, because of the friction of your tires and the bearings in your bike. So the power your muscles will have to provide could be (assuming an system-effectiveness of 90%):
P_mech = P / 0,9 = 181,6W

The energy this process of 10min. requires is:
W_mech = P_mech * t = 181,6W * 600s = 109000Ws = 109000J

But the muscles in your legs aren't the only muscles that work. Your brain, heart and lung, aswell as the overall metabolism require a lot of energy. One can assume that only 22% (muscle-effectiveness) of the whole energy consumption is used by the legs (read in once somewhere that it is about 22% for cycling with vigorous effort):
W_muscle = W_mech / 0,22 = 495,5kJ

This is the energy the motion of your legs requires to climb that hill in 10min.
495,5kJ = 118,4kcal
So you will burn 118,4kcal doing that.


You are right that if you are fitter your muscle-effectiveness might increase and moving them will require more energy. By that the required energy from the body will decrease.

BUT, if you are fitter you will be able to provide more power and climb that hill not with 180W, but maybe with 220W!
And by that faster, which will make you able to climb longer distances in a shorter time period.
So to assume that you will be losing less if you are fitter is simply said wrong.



For the sake of completeness:
This muscle effectiveness depends on many factors...your health (age, fitness-level or muscle-mass, gender and the type of activitiy, because they all stress your muscles differently).
By that it is always hard to really calculate your burned calories with 100% correctness!



What is the crux of the HRMs function to calculate the burned calories?
The problem is that they don't know what type of sport you are doing. By that the muscle-effectiveness for the present case is unknown. Prof. Conconi (a well-known sports-scientist) once discovered that the hear rate correlates with the burned calories in a heart rate zone between 110 - 170 beats/min for cycling.

The only variable factor in that physical equation above is the muscle-effectiveness! By that one can assume that the heart rate correlates with the muscle-effectiveness aswell linear.


So what do the HRMs do...they don't know how much power I provide by my muscles?
That is true, because they don't see what you are doing and how much power you really provide.
But they use the effect of correlating heart rate and burned calories and make very wide-ranging assumptions. Age, height and weight help them to estimate your fitness-level and by that build your personal "factor" for burning calories.

It would be more accurate if the HRM would consider even the type of activity and would require your meassured body fat.
By that it would be possible to reason your overall muscle mass and estimate the muscle-effectiveness more accurate.



In Conclusion:
- Every HRM bases his calorie-calculations on vage assumptions.
- The real and accurate provided power can only be measured mechanically on an ergometer, but even those require a good knowledge of factors like the muscle-effectiveness, which is different for every person
- The HRM works quite well if it is set-up right and the used algorithm used is a good one (trust in the prestigious big manufacturers)
- Don't expect it to be more accurate than to 50-100kcal.