HRM inaccurate for strength training?

jenniebean1680 · January 2012

I have been going to see a nutritionist to help me lose the last 10 lbs, and she told me I am not eating enough. So we're working on 'resetting' my metabolism.

She increased me from 1400/day to 1600 to 1800 and now we're at 2000. I have put on 4 lbs, which she told me to expect, while my body is still thinking it needs to hold onto everything I give it because it's so used to more restriction.

I lift 4x/week, teach spinning classes 3x/week, and run 2-3x/week, with one long run of between 10-16 miles each week.

On days when I lift and then teach my class, I burn between 1000-1200 total, so on those days, in order to net 1300 (MFP and my nutritionist both want this net), I am eating between 2300-2500 cals, and it is tough to eat that much while eating clean. I am also a vegetarian.

My real question is (sorry for all the back story, this is kind of taking over my life), if I'm telling her, based on my HRM, that I'm burning 400-something lifting in an hour and 600-700 spinning in an hour, is that actually correct? I am hearing HRMs are not too accurate when it comes to strength training, which makes sense to me. Should I decrease it by like 200 cals?

I have just started doing circuit training when I lift, rather than more traditional lifting (although I always have liked to move directly to another exercise rather than just sit and rest between sets). I hear circuit training is, coincidentally, an area where HRMs are a little more accurate.

Anyway, what do you guys think? Should I just shave some of that burn off of my lifting, and say I burned 150-250 instead of 400ish? I am sick of trying to find my metabolism's happy place, and if I'm overestimating my burn, it's only going to slow the process even further.

Maddy__H · January 2012

Hi, I do not have the answer to this, but would be interested to hear opinions as well. I do my strength training as circuits, so with little resting, but believe the HRM still shows elevated numbers. As a rule of thumb I try to eat back only 50% of those cals (obviously no science behind this approach). If there is a better way, I am happy to try it : )

xraychick77 · January 2012

LOL

resetting metabolism..seriously.

stop working out so much!
nutritionists dont know everything and they too buy into the diet myths. i cant tell from your picture, but you dont look like you weigh a lot now. eating that much will of course make you gain weight! and HRM's arent the end all and do all of calories burned. they are inaccurate too. there is no way to really tell how much we burn without being hooked to a VO2.

what this nutritionist said does not make sense..so you werent losing, so she told to eat more and you'd lose yet you gained. seems like a no brainer to me. your metabolism is what it is..you cant change it.

you want to lose those last ten lbs..then decrease the exercise, stay around the 1400 calories. it'd be even better if you just took a few weeks off then start back again. you must remember our bodies adapt to what we do to them. they become efficient at using the calories and performing the exercise.

marianne_s · January 2012

No, HRMs are not accurate for strength training because your heart rate is not constantly elevated.

Your best bet would be log a reduced number of calories.

Circuit training is a bit different, because you are doing some form of cardio activity during the session.

I would err on the side of caution where it comes to strength training, and log only 150-200 calories for a 45 minute session. That's usually how much I burn, recorded by my KiFit (UK BodyMedia Fit) when I've done a 40 minute ChaLean Extreme session lifting heavy weights.

HTH

dad106 · January 2012

I wear my HRM during strength training but I don't actually use the calorie count because of how inaccurate they can be for strength training.

The reason why they don't work for it is because it can look like you are up taking more oxygen(Vo2) because of pressure from lifting or over head work, when in reality you are not. Since HRM's use that plus some other things to determine calories burned, it can give a false reading.

rensker · January 2012

LOL

resetting metabolism..seriously.

stop working out so much!
nutritionists dont know everything and they too buy into the diet myths. i cant tell from your picture, but you dont look like you weigh a lot now. eating that much will of course make you gain weight! and HRM's arent the end all and do all of calories burned. they are inaccurate too. there is no way to really tell how much we burn without being hooked to a VO2.

what this nutritionist said does not make sense..so you werent losing, so she told to eat more and you'd lose yet you gained. seems like a no brainer to me. your metabolism is what it is..you cant change it.

you want to lose those last ten lbs..then decrease the exercise, stay around the 1400 calories. it'd be even better if you just took a few weeks off then start back again. you must remember our bodies adapt to what we do to them. they become efficient at using the calories and performing the exercise.

I don't reply often but this comment really pissed me off! What do you know? What makes you knowledgeable enough to tell her to ignore her nutritionist? Also, this was not her question!
I don't have any training in nutrition either but I do have common sense. She does circuit training 4x, spinning 3x, runs 3x a week and only was only eating 1400?! She's also not losing weight on that. There's no way her metabolism "is what it is". Please don't give advice like that anymore, it's already hard enough for women to eat as much AS THEY SHOULD. Look up the group "Women eating 2000+ /day" real women losing eating 2000+ calories. And they don't have "fast metabolisms".

for the OP: HRM are not supposed to be accurate for strength training but you're doing more circuit training than strength training. The reason strength training isn't accurate is because of all the rests, and you said you don't take rest breaks. I'd trust the HRM, 400 calories for 1 hr sounds right.

Azdak · January 2012

I want to correct one thing: the reason why HRMs are not accurate for strength training is not because of the "rests". The reason they are inaccurate is that the physiological mechanism driving the heart rate is completely different from what occurs during cardio exercise.

Therefore, even though heart rate can increase, oxygen uptake does not increase the way it does during cardio. It's the increase in cardiac output/oxygen uptake that is responsible for increase calorie burn NOT the increased heart rate per se.

This is important to understand because the same mechanism is at work (albeit to a much lesser degree) during circuit training as well. Many people still believe that if they move quickly from strength exercise to strength exercise so that heart rate does not go down as much, they are increasing the calorie burn.

Doesn't happen.

The other thing I would add to this discussion is that it sounds like you are expecting way too much precision from your HRM. The accuracy of HRMs to estimate calories is about 80% at best.

HRMs are most accurate only if:

They are set up correctly, with your actual HRmax and a close estimate of VO2max.
You are performing steady-state cardiovascular exercise at an intensity below your anaerobic threshold.

Under any other conditions, they become even less accurate than 80%.

Other than that, I would tend to agree with you eating a larger amount of calories for the work you are doing.

10kaday · January 2012

What Azdak says here makes complete sense! When I tested my HRM with strength training it said I burned 400 some calories. I just didn't believe that could possibly be right. I checked what MFP said and it was only 130 calories which seemed more realistic to me. So, I now follow that.

HRM inaccurate for strength training?

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