how accurate are the exercises?

I feel the same way, I've been wondering this as well. For those of us who don't have a HRM, what should we do?

bump, I have been wondering about this also

IMO, the MFP exercises are based on the average amount of calories burned in that time. I got a HRM so that I know within a small percentage of inaccuracy of what I am burning.

For example I went to a 90 minute and fast paced walk/jog in 95 degree dry heat yesterday, MFP said it was about 450 calories for me and my husband (who has 9 inches and 70 lbs more than me) and my HRM said 800. Based on how hard I know I pushed myself, how winded I was, the heat which I'm not use to and how satisfied I felt I trusted my HRM more.

I was just using MFP at first, and then got an HRM. What I found was that I was underestimating my speed and such.

Like, for instance, I'd put that I did 40 minutes of walking 3.0 mph and it would give me a total of 300 cals.

My HRM doing that same trail for 40 minutes burned about 470, which was actually the walking, 3.5 uphill speed.

Make sense?

MFP uses METs, aka metabolic equivalents. METs are basically the average burn as estimated in a lab setting based on the individual in that it is estimated that we burn 1 MET per hour. 1 MET is equal to 1 kilocalorie (what we all call calories) per kilogram of body weight per hour or 3.5 ml of oxygen per kilogram per minute if you are using it for VO2 calculations. So, if you are going by VO2 while exercising you are also sort of going by METs. But most people don't have access to metabolic cart equipment to go by VO2. If it has been found that an exercise burns 7 METs then it burns approximately 7 kilocalories per kilogram of body weight per hour. So a lot of calorie calculators just multiply the MET level by your weight in kilograms to get your calories per hour and then divide by 60 to get calories per minute and multiply by the minutes you did the exercise to get your calories for that time. When doing this calculation, you should subtract out the 1 MET you would have burned without doing the exercise and I'm not sure if that is done on MFP or not.

The calculators on machines use any number of formulas for determining their calorie burns. Some just do an average of what they have found people burn on their equipment, others base their calorie burn formulas on a 150 pound man (this use to be the standard so if you have an older piece of equipment, its only accurate if you are a 150 pound man), and still others actually use the information you program in and in combination with your heart rate come up with an estimate of calorie burns. So the accuracy of your calorie estimate from a piece of equipment is only as good as the piece of equipment. Also, if it uses the heart rate or if you use a heart rate monitor, they can be thrown off by consumption of caffeine or medications that you may be taking because they effect the heart rate. I don't burn the same amount of calories while I'm on the treadmill and have a heart rate of 130 as I do while I'm sitting on my couch and have a heart rate of 130 from my asthma medication, but the HR monitors see it as the same.

Basically, what I'm saying is that none of the methods are 100% accurate, so just take the one you like best or is most accurate for you (IE: not a heart rate based one if you are on asthma, allergy, blood pressure, or other cardiac meds) and use it as a guide. Or you can contact your local university and see if they have a human calorimeter you can go live in, but since everything that goes into and comes out of the body has to be measured, I don't recommend that. It's kind of a gross process.