Frustrated with hrm...

I've no idea what a p90x plyox is... but, for max calories/hour burnt you need to need to do cardio stuff that works the big muscles of your body (legs and bum) ... the best things are running, cross-country skiing, rowing, cycling.

That's not to say that you shouldn't do other stuff as well... variety is the spice of life, and strength training has other benefits than purely calories burned.

Of course the calories burned depend on your weight too... smaller people burn fewer calories.

I've found many machines and HRM's to be out to lunch on actualy calories burned. My gym has two different brands of machine and on one If i use heavy intervals of resistance for 30 minutes i can burn almost 500 calories. It takes into account my weight, age, and uses that to get an accurate reading. The other machine does not uses that info and can barely get to 300 in the same time. Chances are the HRM you have isn't calculating baes on the activity/weight/age and just giving you a general idea of calories lost at that heart rate.

Not trying to be mean, but your anger is misplaced.

HRMs are passive devices--they do not measure ANYTHING except heart rate.

ANY information about calories is an estimate of varying accuracy. Even the most accurate HRMs, with the most accurate setup information are, at best, about 80% accurate. The method that HRMs use to estimate calories is only valid under certain exercise conditions.

The manufacturers of HRMs have done an excellent job of marketing their devices and creating the image that they are simple "plug and play" devices that can accurately measure calorie expenditure during exercise. They have been assisted in this task by our natural human impulse to want simple answers to complicated questions and to place great faith in numerical displays.

If your HRM is giving you numbers that you think are not accurate, it is probably due to one of the following:

1. You have a lesser quality device. Any HRM manufacturer can include a "calories burned" display on their device. Only a few companies have developed prediction equations that are acceptably accurate--the only ones I know of are Polar and Suunto.

2. Your HRM is not set up properly. Accuracy of calorie estimation, such as it is, requires that the HRM have your accurate age, weight, sometimes gender, sometimes height, sometimes general activity level, and it must have some way of determining your fitness level. To determine fitness level it can include some type of "Fitness Test" (some Polar models), or it must allow you to manually enter your VO2 max. Without this information, the HRM is just estimating your fitness level, which just adds to the inaccuracy.

3. You are not using a chest strap transmitter, or there is a contact/transmission problem with the chest strap transmitter. If you are not getting a continuous transmission of heart rate, your calorie estimate will be way off. This kind of goes back to #1.

4. You are using the HRM during activities for which the calorie estimation equations built into the HRM arent' accurate--examples: daily household activities, at rest, lifting weights, doing high-intensity interval work, doing exercises that involve a lot of upper body movements; also conditions such as thermal stress. Usually these conditions lead to an HRM OVERestimating calories, rather than underestimating, as seems to be your concern.

Now, at you weight (which appears to be under 60 kg), your calorie expenditure is going to be lower than average anyhow, so this is something to keep in mind. Even if you were running, say a 9 minute mile pace, you would still barely be at 600 calories an hour.

For something like P90x where there may be some stopping and starting involved, it can drop the average down. Does your HRM have an "average heart rate" feature? You mention that your heart rate was at 75%-80% of max "the whole time"--the average heart rate recorded for the workout should reflect that. If not--if the average is lower than 75% of your max--then that might be the explanation right there--your exertion is not as continuous as you think.

Not saying any of these apply to your, since I don't any more details, but these are just some of the more common reasons why you seeing the numbers you are.

Unless you have lost weight, if you are running a 5K at the same speed you were running before, you are burning the same amount of calories. If you are running faster, then you are burning more..

I agree with pretty much all you've said, but I did just want to comment on this.

Part of the point of running training is that you improve your running efficiency. So, in the long term, you hope to be able to run the at the same speed for lower energy expenditure or, alternatively, run faster for the same energy expenditure.

I know a few people that are in your weight range that do not burn more than 400 calories during P90X plyo. I am 217 lbs and can burn around 700 calories according to my hrm. So, for someone lighter in weight you're going show a lesser burn.

As Azdak said, update your fitness info. I saw from your profile that you've lost weight. Maybe that needs to be updated. If your hrm requires that info.

If you are referring to mechanical efficiency, those "increases" will be relatively insignificant. A study was just published that look at the pedaling efficiency of elite cyclists. A group of 12 elite cyclists were tracked over five years. It was determined that their mechanical efficiency increased by an average of 3% total. That's over 5 years in athletes whose only profession is training and racing. Granted, that does not directly apply to running, but the principle is still the same.

There is a period of adaptation when starting any sport, so, yes, larger improvements in running efficiency will occur in beginners. However, their fitness levels will also increase more rapidly. As time progresses, VO2 max may plateau, but further increases in performance can still be achieved. At that point, additional increases in mechanical efficiency will be minute. Some performance increase can be achieved via strength conditioning, but most increases will occur because of an ability to utilize a higher percentage of VO2 max and sustain it for a longer period of time. Bottom line: you are still working harder, even if perceived exertion remains the same.

Right, the changes can be relatively small... but whether you regard them as "insignificant" is a matter of perspective. For a highly trained athlete a 3% improvement is huge... that would mean Haile breaking the two hour barrier for the marathon.

I suspect, although I don't know for sure, that there's more scope for improvements in running efficiency amongst inexperienced runners than cyclists, because there's a bigger variety in running gaits than in pedalling styles.

Incidentally there are other things than just VO2 max. This is the main thing for middle distance runners, but for marathoners whilst VO2 max is still important, there are other important features that improve with training that have an impact on efficiency - for example improved glycogen storage in the liver and muscles. This is important because as glycogen starts to run low more of your energy come from metabolising fat... which takes more oxygen than metabolising glycogen; so your heart and lungs have to work harder to deliver the oxygen needed for the same energy output - so less of the total energy you're expending is being spent propelling you forwards.