HRM question - why do I burn so much less than my friend?

SJ46

You DO NOT burn more calories because you are less fit. Absolutely not.

I don't have time to go into details, but the answer is just no, no, no, no, no, no, no.

The decrease in calories burned displayed on an HRM as one trains and improves fitness is a HRM anomaly. It is an error in the HRM, not in your body.

Really? Fascinating. I hope you have the time to come back and explain, I've learned a lot from you in the short time I've been here RE HRMs.

jett254

You DO NOT burn more calories because you are less fit. Absolutely not.

I don't have time to go into details, but the answer is just no, no, no, no, no, no, no.

The decrease in calories burned displayed on an HRM as one trains and improves fitness is a HRM anomaly. It is an error in the HRM, not in your body.

Hoping you have the time now to come back and explain more - this was a very interesting post and I keep seeing my HRM calories burned go down slowly over the course of several months.

Azdak

You DO NOT burn more calories because you are less fit. Absolutely not.

I don't have time to go into details, but the answer is just no, no, no, no, no, no, no.

The decrease in calories burned displayed on an HRM as one trains and improves fitness is a HRM anomaly. It is an error in the HRM, not in your body.

Hoping you have the time now to come back and explain more - this was a very interesting post and I keep seeing my HRM calories burned go down slowly over the course of several months.

One of these days I have to do a whole blog on this, but here is the quick version:

Heart rate is a relative and indirect measure of intensity during aerobic exercise.

The real measure of intensity (and thus calories burned) is oxygen uptake, or VO2.

A person's range of fitness (VO2) goes from rest to VO2 max (i.e. the most amount of oxygen that can be used by the body).

A person' s heart rate range goes from rest to HRmax.

During aerobic exercise there is a consistent relationship between heart rate and VO2. You just have to have the right "scale". In other words, you have to know HR rest, HR max and VO2 max. If those values are known, then we can "fit" the two scales together and we can use heart rate to estimate intensity--which is good, because heart rate is easy to measure, whereas measuring VO2 requires expensive lab equipment.

Example: if someone has a VO2 max of 10 METs and they are working at 70% of heart rate reserve (or 85% of HRmax), then we can estimate that they are working at 7 METs. If they weight 70 kg (154 lbs) we can estimate calorie burn at 490 kcal/hr. (7 x 70).

HRMs don't work exactly that way, but their calculations are based on that physiological relationship.

With training, you max aerobic fitness level can change --that's the whole point of training, right?. However HR max stays the same. HR rest can change as well.

Since heart rate stays relatively the same, if VO2 max increases, you now have a different "scale". Let's say VO2max is now 12 METs instead of 10. If you work at the same 7 MET workload, your heart rate will now be at 58% of HR reserve instead of 70% (7/12ths instead of 7/10ths).

However, 7 METs is still 7 METs. Unless your weight has changed, the calorie burn is the same. It feels easier and heart rate is lower because your max level has increased--so that same workload and same calorie burn feels easier and is achieved at a lower heart rate.

But the HRM will show a lower number. Why? Because the HRM doesn't know your VO2 max has increased. It assumes that your max is still 10 METs and it assumes that you are working at a lower workload, thus burning fewer calories.

Again, unless weight has changed, you are NOT burning fewer calories. It is a HRM setup error. It's a testimony to the marketing power of Polar, and the inexplicable level of blind faith that people have concerning HRMs that fundamental concepts of exercise physiology have been turned upside down based on reflexively generated numbers on a watch face.

How do you adjust your HRM? If you have a model that allows manual entry of VO2max, it's an easy adjustment. If you don't have that feature, then I'm not sure how to do it. HRMs use proprietary algorithms that those of us on the outside have to guess at.

twinsmom03

bump

SJ46

Thanks for coming back with such a thorough explanation.