Do HRMs work for weight lifting re: calorie burn?

I use mine for circuit training. I do a 20 min cardio warm up and my hr will stay pretty constant while lifting especially if I don't rest too much.

Not for calorie burn no...

Your HR is not directly correlated to your calorie burn...it is just used in an algorithm that assumes steady state cardio in order to get a reasonable representation as to what level of VO2 max you are working at. Weight lifting is an anaerobic activity and is a ****ty indicator of VO2 max, thus HRMs are going to be inaccurate.

The further away from a steady state cardio event you are, the less accurate it is going to be for calorie burn.

Hmmmm I use my HRM while I do my workouts. Which consist of 35mins on the elliptical keeping my HR above 140 and do a max of 170. When I get off I go and strength train from anywhere between 30-40mins and I dont let my HR drop lower than 100. So it's usually between 100-130.

I stop my HRM when I'm done and it is usually around 500-600 calories depending on how intense my cardio was.

So based on that my calories burned is inaccurate because a HRM doesnt accurately monitor calories burned when strength training?

But surely if your heart rate is up you are burning calories. I bought a polar ft4 yesterday and had it on whilst working today ( I'm a self employed gardener) my average rate was 95 with a max of 145 and burned 2750 cals. When I was in my 20s I did a lot of weights and know that my heart rate was up. So surely it would still be counting any calories that are burned during exercise.? I may be wrong but it seems logical to me..

You're burning calories while sleeping, too. The algorithms used by HRMs to calculate calories simply are not accurate for anaerobic activities. The concept that your heart rate is elevated, so you're doing something right is flawed. Do you lose weight from watching scary movies or riding roller coasters? (after all, both raise your heart rate)

I watched a scary movie and lost weight, after I changed my pants.

First thing to understand: HRMs do not measure calories burned! They measure Heart Rate.

Next thing to understand: A faster beating heart does not burn significantly more calories. You can check this yourself by sitting perfectly still and hold your breath as long as you can. Repeat over and over. Watch your HR soar. Are you burning more calories? What if you burn 100 calories in a walk, then repeat the walk the next day immediately after having 3 cups of espresso. Are you burning more calories? No. Well, your HRM will say you did.

Important bit about HRMs: They use a CALCULATION based on the volume load from steady state aerobic exercise.

Volume load: When doing aerobics, your HR rises to move a greater volume of oxygen through your body. When you lift weights, your HR rises while blood vessels constrict to increase the blood pressure in the appropriate area. So, the calorie formula is no longer accurate.

Steady state: When you are doing aerobics, you are constantly moving with very little rest, and you are moving large portions of your body. When you lift weight, you are often not using your whole body, and taking longer rests. So, it's not accurate.

Aerobic exercise: Aerobic exercise is when your body mixes oxygen and fat to produce energy. This happens when the energy requirement is low. Lifting weights is anaerobic exercise. That means it uses the glycogen stored in the muscles for energy. Different energy source from aerobics (what most people call cardio), so the formula is inaccurate.

To recap: The three important factors in determining a calorie burn from HR are all using DIFFERENT THINGS. There is NO WAY for it to be even remotely accurate.