Garmin tracking less calories for the same exercise

The calculators assume a steady heart rate, garmin tracks it I'm assuming. The one monitering your heart rate consistently is going to be more accurate.

HR is going to be the most accurate. As long as it is accurately tracking it.

I don't go by my Garmin numbers, but by MFP's calculation. When it's hot, my HR increases significantly. That doesn't mean I'm burning more calories, just that I'm hot. When I run a hilly course, my HR increases and stays up even when I'm not doing the hills. I've noticed with my watch that in a single run my burn varies quite a bit and is definitely higher than I get using weight x distance x .6. On a recent run, it went between 77 and 96 calories per mile.

slbbw wrote: »

Weight has dropped about 10lbs. Yes that accounts for some of it. Two weeks ago it was tracking at ~95 calories per mile and today was at ~75 calories per mile. My weight has not changed substantially n 2 weeks. My average HR dropped from 150-160 to 140-150 depending on the length of the run.

My concern is that all of the running calculators say average is about 100 calories per mile. 75 calories per mile is significantly lower than that. Is HR still an accurate way to track this?

Re. "My concern is that all of the running calculators say average is about 100 calories per mile."
For who? For you in particular or for someone who weighs 100lbs or weighs 300lbs?

Re. "Is HR still an accurate way to track this?"
HR was never an accurate way to track exercise burns - there isn't a set correlation between number of heartbeats and energy expenditure. It might by chance to be an ok way for some people (the complete reverse is also true) but it's very varied between individuals and as you are discovering variable for an individual with changing fitness levels.
For example as I got fitter my resting HR dropped by 20% (60 to 48) yet my calorie burns (measured by power produced) went up by 25%. That's just a function of my CV systems working better, predominately pumping more blood for each heartbeat,

You could just use the running calorie formula weight in lbs X distance in miles X efficiency ratio of .63 for an estimate based on the physics of moving mass over distance. Or simply accept that exercise calorie burns are an inexact art, you can't measure energy with a watch and use your Garmin estimates as they are for simplicity.

BTW - I use my Garmin estimates for cycling even though they are significantly low for a good proportion of my cycle rides. You only need to aspire to reasonable not absolute accuracy for the purpose of calorie estimates,

Heart rate is a proxy for calorie burn, so what you get is an estimate of calorie burn, not a measurement of calorie burn. The idea that heart rate monitors or fitness trackers are the best way to estimate calories for every exercise is sadly false.

It sounds like you're getting fitter (doing the same work, i.e., same distance in the same time) at a lower heart rate. That's a wonderful thing!

Unfortunately, that makes some trackers think you're burning fewer calories. But at the same bodyweight**, running the same distance in the same amount of time is burning pretty close to the same number of calories. (** I noticed that you said you've lost 10 pounds, OP; that seems disproportionate to the results you're getting from your device. HR plus weight reduction might account for it, but things like ambient temperature and dehydration (and stress and more) also affect heart rate, so I dunno.)

These are a good read on the subject of heart rate monitors and exercise (oldies but still goodies):

https://www.myfitnesspal.com/blog/Azdak/view/the-real-facts-about-hrms-and-calories-what-you-need-to-know-before-purchasing-an-hrm-or-using-one-21472
https://www.myfitnesspal.com/blog/Azdak/view/hrms-cannot-count-calories-during-strength-training-17698

I'd note that some of the newer devices that measure many variables besides heart rate (such as distance, speed, elevation change, etc.), that include "fitness tests" you can perform, that know your demographics, and that know what specific exercise you're doing (running vs. biking, say) have the potential to do a bit better job of estimating calories, but I'm not convinced that they all take advantage of that potential in their algorithms.

An additional complicating factor is that if you don't know your actual max heart rate, but instead are relying on an age estimate of HRmax, the whole heart-rate-tracking view (training such) may be misleading. (When one lets the device estimate HRmax, many/most of them use an age-based estimate.) The age-based formulas for HRmax are inaccurate for a fairly large percentage of people. (This has less to do with fitness, and more to do with genetics.)

Believing a fitness tracker or heart rate monitor is gospel for calorie burn is more of a religious view than a scientific one. In a lot of scenarios, they may be the best tool we have, but it's a good plan to understand their limitations.

I'm hoping someone who actually runs will chime in with the rule-of-thumb formula for estimating net calories from running (a lot of devices are estimating gross exercise calories, i.e., BMR is included).

Best wishes!