For those of you that have heart monitors....

Thanks everyone...sounds like a pretty good consensus for this group.

The make of HRM also makes a difference. I had what I thought was a very nice Timex Triathlong HRM. The HRM portion was fine (although it doesn't sync with gym equipment), but the calories burned calculation was horrible! It read between 2 and 3 times too many calories burned...

After much, and I mean MUCH research, I bought a Polar and haven't looked back.

I got the FT80 at a bargain price through BodyTronics (GREAT people to work with) but most probably don't want to spend that much, and I totally understand. Both the FT4 and the FT7 are very popular, and can be had for well under $100.

Just be sure that whatever you get has batteries that you can replace yourself, and not have to send the unit in.

From my own experience it all comes down to Training Zones and whether your HRM and the Gym Equipment are close when it comes to calories burned. Here is a basic breakdown of Training Zone:

TRAINING ZONES

Healthy Heart Zone (Warm up) --- 50 - 60% of maximum heart rate: The easiest zone and probably the best zone for people just starting a fitness program. It can also be used as a warm up for more serious walkers. This zone has been shown to help decrease body fat, blood pressure and cholesterol. It also decreases the risk of degenerative diseases and has a low risk of injury. 85% of calories burned in this zone are fats!

Fitness Zone (Fat Burning) --- 60 - 70% of maximum heart rate: This zone provides the same benefits as the healthy heart zone, but is more intense and burns more total calories. The percent of fat calories is still 85%.

Aerobic Zone (Endurance Training) --- 70 - 80% of maximum heart rate: The aerobic zone will improve your cardiovascular and respiratory system AND increase the size and strength of your heart. This is the preferred zone if you are training for an endurance event. More calories are burned with 50% from fat.

Anaerobic Zone (Performance Training) --- 80 - 90% of maximum heart rate: Benefits of this zone include an improved VO2 maximum (the highest amount of oxygen one can consume during exercise) and thus an improved cardiorespiratory system, and a higher lactate tolerance ability which means your endurance will improve and you'll be able to fight fatigue better. This is a high intensity zone burning more calories, 15 % from fat.

Red Line (Maximum Effort) --- 90 - 100% of maximum heart rate: Although this zone burns the highest number of calories, it is very intense. Most people can only stay in this zone for short periods. You should only train in this zone if you are in very good shape and have been cleared by a physician to do so.

I spend no more than 5 minutes total between Zone 1 and 2 and make sure I am into the 3rd zone (Aerobic Zone) and stay there throughout my workout. I have a FT60 and have experimented on every piece of equipment at my YMCA and the biggest example I can give of what I am talking about is on the treadmill. I have severe knee problems which require me to where braces and I can only walk (no choice, can not run) and no matter what incline I set, I can't get enough speed to get my heart rate out of zone 1. So monday I did 1 hour on the treadmill and did an avg. incline of 8 and 2.8 mph. (bout as fast as my knee's will let me go) and after the hour was up the treadmill said I burned 906 calories, my Polar FT60 after that same workout said 660 calories.(Big Difference!!) Now switch to the Ellipitcal (Precor 576i) and today i did crossramp training up to level 20 and back down in 1 minute increments with a resistance set at 11 and in 81 minutes the machine said a burned 1238 calories and my FT60 said I burned 1270 calories... But I only spent 5 minute warmup getting my heart rate into zone 3 and then kept it there. Once you get your hear rate up into those higher zones it is much easier to keep it there... Hope that helps....

to answer the question posed: sometimes. All are based on simple equations. The more accurate the information going into those equations, the more accurate you will get with your calories burned calculation. So, use a HRM to measure avg HR, you'll also need age (rounded fractionally), accurate weight, and accurate time working out. Try this calculation (for MEN):

(.6309 * avg hr + .09036 * weight + .2017 * age - 55.0969) * minutes / 4.184

I use 90% of that as my calories burned number for MFP logging.

My biggest one is the Eliptical Machine...at some points it will tell me I have burned as little as 80 calories in 15 minutes and my HRM (with chest strap) says as high as 147-168!

I guess the best you can do is figure out your target HRM for fat burn zone and try to stay with in that and do intense cardio where you woulr burn about 10 calories a minute.

My HRM is generally much higher than the machines at the gym or even MFP, which I don't really understand because MFP also has my age, height and everything. For example, yesterday's cardio workout - MFP said I burned 322 calories, RunKeeper said 316, and my HRM said 488!

It's a Polar FT7 which I got for Christmas - I really like it so far, it's a neat little gadget.

This is going to sound rather flippant, but...
put two fingers on your carotid artery (neck) and count the pulse for a given length of time. Works every time and is 100% accurate (and doesn't cost a penny)!