BMR & Total Calories

It's my understanding that the activity is based on your active HR over your resting HR.

Yes, activities such as biking and running are based off your active HR. I'm asking how they come up with their numbers for BMR (Basal Metabolic Rate) and the calories burned from normal activities (i.e. - steps.) There is no way that my BMR is over 2100 calories/day, and I doubt an average of 7500 steps/day (or walking roughly 3.4 miles) would burn an additional 800-1000 calories/day. These are my calculations BEFORE you tack on the calories burned from tracked activities.

I use Cronometer to log my food because it is so much better than My Fitness Pal and its calculations along with my activity calories (from when I was using a fitbit but it looks about the same with the garmin) seemed to be pretty spot on. My basal in cronometer is about 400 calories lower than Garmin thinks it should be. I don't even bother with what Garmin thinks (or what My Fitness Pal thought) I should eat.

On the FR235 there was a user setting for "activity class" that you set from 1-10 based on how active you are. The higher the number, the more active. Using a program I downloaded a couple of years ago, you could view your FIT files in an EXCEL spreadsheet. Based on what activity class you selected, it would also change your BMR calories. I have no idea what calculations Garmin was using, but I had to set my activity class at 7 to get what I thought was my correct BMR calories. Unfortunately, you needed this program to see the setting because the information wasn't displayed anywhere else. Anyway, I just checked Garmin Connect and the activity class setting is still available for the FR235, but not for the VA3. I don't know if it's a hardware or software thing, but maybe it's something that can be requested for the VA3.

I have contacted garmin about this a couple of weeks ago. I gave them a very detailed description of what the problem is and how to fix it, together with references to scientific articles about BMR and its estimation. I asked them last week if they made any progress and they replied that the issue was forwarded to the technical guys and when they fix it they will let me know.

In principle, for any HR tracker there should be no multiplier for activity. If you are able to measure HR 24/7 you can very accurately estimate the caloric expenditure. Also, resting calories are always the same and depend on height/weight/age/(fat percentage, not crucial). This is super easy to calculate. Active calories can be estimated (and actually are estimated) based on HR during workouts and steps taken (maybe HR changes during the day? dont know, and they would not tell me saying its confidential).

The mistake garmin is making, is they double the actively burned calories. Their resting calories is BMR*activity multiplier, and on top of that they add active calories. You can see that your resting calories is around 1.2*BMR (actually surprisingly close to a perfect 1.2 multiplier, which is what i think they actually did, and a 1.2 multiplier is usually used for a moderately active person, when you DONT track your activities).

Multiplying your BMR by 1.2 or something close, depending on how active you are, is a very good idea when you have no ability to track your active calories. In ancient times without HR smartwatches thats what every athlete/bodybuilder did.
Katch and McArdle in their famous book "Essentials of Exericse Physiology" give a very nice table of multipliers you should use according to how often you work out and what your job is.

However, using a HR smartwatch, we should be able to estimate everything much more accurate, so there should be no multipliers, just pure BMR - resting calories, and Watch measurements - active calories. And those two summed up should give your TDEE.

Lets hope garmin finally understands it and fixes that, this shouldn't take them more than 5 minutes to fix, they just have the BMR formula multiplied by something, which should be just removed. As far as i know, the active calories are estimated pretty accurately so no fix need there.

EDIT: Trackers that do not have HR measurements should keep the multiplier, and the additional calories that go over BMR due to the multiplication should be gradually added as "Active calories" throughout the day. That would still be pretty accurate since they have no access to HR measurements.

Emil, that is actually what Cronometer (A food app) says to do. If you use a fitness tracker you set the activity to "none" and they import the activity calories from the fitness logger. Since I am on a weight loss plan, I was surprised at just how accurate they were when I exported my calorie deficits over a 6 week period, summed them up and divided by 3500 the weight loss was within .25lb of what was predicted. Garmin connect can sync with Cronometer but will not import food calories from them even though the Cronometer app will allow it. (Another request)

I totally agree with you and wondered if you got anywhere with this, as far as i can see Garmin are still multiplying mine by 1.2 even though I am using a Fenix5 with HR.

Thanks again Matt.