just trying to understand how calorie burn works

ractayjon

There are a lot of posts on the site with people asking - is the calorie burn accurate? what do I use the machine or my hrm? the site tells me one thing but I think another etc etc....

Im wondering how does your body burn a calorie? I do the shred DVD (I have a hrm) and one day I burn 180 calories, the next 190 the next 230, I understand that exertion has something to do with it....I run and my calories burned are WAY lower then others running. I see people post their exercise and so and so burnt 500 calories doing something for X minutes....when I do that same exercise for the same minutes I burn 250. Iknow everyone is different - but I am wondering if someone can explain HOW calorie burn works (or direct me to somewhere that can explain it) thanks

imagymrat

compliments of the Mayo clinic


Metabolism is the process by which your body converts what you eat and drink into energy. During this complex biochemical process, calories in food and beverages are combined with oxygen to release the energy your body needs to function. Even when you're at rest, your body needs energy for all its "hidden" functions, such as breathing, circulating blood, adjusting hormone levels, and growing and repairing cells.

The number of calories your body uses to carry out these basic functions is known as your basal metabolic rate (BMR) — what you might call metabolism. Several factors determine your individual basal metabolic rate:

■Your body size and composition. The bodies of people who are larger or have more muscle burn up more calories, even at rest.
■Your sex. Men usually have less body fat and more muscle than do women of the same age and weight, burning more calories.
■Your age. As you get older, the amount of muscle tends to decrease and fat accounts for more of your weight, slowing down calorie burning.
Energy needs for your body's basic functions stay fairly consistent and aren't easily changed. Your basal metabolic rate accounts for about 60 to 75 percent of the calories you burn every day.

In addition to your basal metabolic rate, two other factors determine how many calories your body burns each day:

■Food processing (thermogenesis). Digesting, absorbing, transporting and storing the food you consume also takes calories. This accounts for about 10 percent of the calories used each day. For the most part, your body's energy requirement to process food stays relatively steady and isn't easily changed.
■Physical activity. Physical activity and exercise — such as playing tennis, walking to the store, chasing after the dog and any other movement — account for the rest of the calories your body burns up each day.



Just a little side note, I always take 25% off the number of cal burned if I find I need to use a machine number or a website, they can be anywhere from 10-50% off in their accuracy...which is also why some people don't see weight loss results a quickly, they're eating back exercises calories that they perhaps have not burned off, but have assumed so because a machine told them that..know what I mean?...unless you have a good quality HMR and even then they can be off...it's a tough one to know exactly what you've truly burned away.

arewethereyet

have you checked to be sure the HRM is set up correctly?

I had mine set up with the wrong numbers and it was far off from what I was burning.

arewethereyet

http://www.myfitnesspal.com/topics/show/69708-calorie-deficit-for-dummies-a-little-long

some good info from Banks here

mromnek

Just a side note that dovetails with gymrat's post: My wife and I use the same model HRM. I set both of them up (so they are set up using the same methodology). When we go walking together, she burns between 30 and 50% of the calories I burn. Simply put, I weigh quite a bit more than she does. So, from a simple physics standpoint, it takes more energy to move me 1 mile than it takes to move my wife 1 mile.

Your HRM is only measuring 2 things, heart rate and time. From there, your HRM estimates your calories burned using your heart rate, weight, sex, maximum heart rate, resting heart rate, and if it calculates it VO2max. Every HRM manufacturer uses a slightly different method of calculating the calories burned... so I will get different responses from different HRMs. I can't tell you which is the most accurate (as I am still trying to weed through the self serving information to get a clear answer myself).

What I have been able to glean from the reading I have done is this:
1. A HRM with a chest strap is "generally" more accurate than 1 without. (I have seen a lot of chatter about the BodyBugg, but have not looked into this at all.. so I can't address this) Actually, this claim may be more subjective than objective.
2. A HRM that asks for, or calculates your VO2max is more accurate than one that does not. I am not certain about this, as the formulas I have seen appear to not require this.
3. The HRMs on machines are generally not as accurate as dedicated HRMs. The HRM on my NordicTrack exercise bike is nowhere near accurate. As I have heard, they are installed more as a gimmick than anything else.
4. The calorie counts on machines is grossly inaccurate, as they are at best based on averages, and at worst, just guesses.
5. The calorie counts on websites varies between somewhat accurate to best guesses.

Sorry to say, but your question about HRMs drives deep into the murky realms of fitness, where almost every claim has some element of profit attached to the claim. Finding objective information at that level is extremely difficult for the average person. But keep digging... someone will find truth and be able to share it with others.

Azdak

Just a side note that dovetails with gymrat's post: My wife and I use the same model HRM. I set both of them up (so they are set up using the same methodology). When we go walking together, she burns between 30 and 50% of the calories I burn. Simply put, I weigh quite a bit more than she does. So, from a simple physics standpoint, it takes more energy to move me 1 mile than it takes to move my wife 1 mile.

Your HRM is only measuring 2 things, heart rate and time. From there, your HRM estimates your calories burned using your heart rate, weight, sex, maximum heart rate, resting heart rate, and if it calculates it VO2max. Every HRM manufacturer uses a slightly different method of calculating the calories burned... so I will get different responses from different HRMs. I can't tell you which is the most accurate (as I am still trying to weed through the self serving information to get a clear answer myself).

What I have been able to glean from the reading I have done is this:
1. A HRM with a chest strap is "generally" more accurate than 1 without. (I have seen a lot of chatter about the BodyBugg, but have not looked into this at all.. so I can't address this) Actually, this claim may be more subjective than objective.
2. A HRM that asks for, or calculates your VO2max is more accurate than one that does not. I am not certain about this, as the formulas I have seen appear to not require this.
3. The HRMs on machines are generally not as accurate as dedicated HRMs. The HRM on my NordicTrack exercise bike is nowhere near accurate. As I have heard, they are installed more as a gimmick than anything else.
4. The calorie counts on machines is grossly inaccurate, as they are at best based on averages, and at worst, just guesses.
5. The calorie counts on websites varies between somewhat accurate to best guesses.

Sorry to say, but your question about HRMs drives deep into the murky realms of fitness, where almost every claim has some element of profit attached to the claim. Finding objective information at that level is extremely difficult for the average person. But keep digging... someone will find truth and be able to share it with others.

A couple of additions:

1. Saying that machine calorie counts "are at best based on averages" is inaccurate in a couple of ways. First, a number of manufacturers use accepted energy prediction equations (e.g. from the American College of Sports Medicine) to predict calories. Second, some manufacturers develop their own machine-specific calculation algorithms, based on research performed in their own labs or contracted out to universities. Finally, in a larger sense, all of these methods--machines and HRMs use "averages" in the sense that they all use validation studies on selected groups to develop equations that they generalize to the population as a whole. The equations/algorithms they use all have standards of error.

2. It is true that some manufacturers exaggerate their calorie counts, or use "guesstimates"--but so do a lot of HRM manufacturers. The cheapo HRM that you buy at a discount store does not have the same level of research behind it or accuracy as a Polar top-end model or Suunto, just like the lower-rank treadmill or cross trainer doesn't have the same accuracy or research as a Life Fitness model. Some equipment manufacturers (Concept 2 for example) make it clear up front that their calorie count is just a representative example and not intended to be accurate. A number of HRM manufacturers do the same thing, but they would never admit it.

3. It is ironic that although, as a whole, machines are probably less accurate than the top HRMs (because manufacturers do such a sloppy job in their calculations), the basis for their calculations is more "real" than HRMs. By that machines attempt to estimate the actual energy cost of the activity, whereas HRMs just measure heart rate. Heart rate can vary during the course of a workout, even with no change in intensity. If you run at the same speed on a treadmill for 45 min, your heart rate can be 10-20 beats/min higher at the end. The intensity of the activity hasn't changed, but the HRM will count more cal/min at the end than at the beginning. Machines don't do that. When I do a 45 min workout on my stairmaster, my HRM (Polar F11) will count as much as 25% higher calories during the second half of the workout, compared to the first half, even when I have not changed the intensity. Did it undercount during the first half or overcount during the second half? Or both?

4. No HRM can "measure" VO2 max. If you are using an estimated VO2 max (e.g. the Polar resting HR "ftiness test"), you are adding another "guesstimate" and standard of error on top of the "guesstimate" and standard of error from the HRM calorie estimation software itself.

Good HRMs are great tools and, especially if you do a lot of different aerobic activities, the calorie counts are probably good ballpark figures that you can use in planning your program. But they are not precise--not even close--and should not be considered any better that 80% accurate--and that's for the Polar F6 type model with a chest strap. Personally I would never "eat back" more than 50% of the exercise calories estimated by any method.