It's EXTREMELY difficult to burn 1200 calories/hour unless you're a very large, extremely fit, heavily muscled athlete doing a very intense exercise that you can actually sustain for the full 60 minutes. That study about calorie burning during kettlebell workouts that was linked in one of the earlier posts in this thread says, for example, that the subjects did burn 400 calories in a 20 minute workout. That would translate into a calorie burning rate of 1200 calories per hour--but only IF the subjects could actually maintain that level of intensity for the full 60 minutes. Very few people can do that, and those subjects didn't.
Most of us ordinary mortals doing an exercise that we can actually maintain for 60 minutes aren't working at nearly the kind of intensity level that it would take to burn 1200 calories. Typically, we might work that hard for brief intervals during a high intensity interval training type of cardio workout, or for several fairly brief intervals during a very vigorous strength training workout. But if you spend a significant amount of your time doing lower intensity intervals or resting during your workout, that's going to lower your total calorie burn dramatically.
Here's a good way to check the validity of claims about hourly calorie burning rates for various activities that you might do, and also to get an idea of whether exercise trackers or on-line programs for estimating exercise calorie burning are giving you a realistic estimate.
Start by using a standard formula or calculator for estimating your resting metabolic rate. That's the number of calories someone your age, weight and gender would likely burn in 24 hours if you do nothing but lay in bed all day. Here's a good website with a calculator like this:
Then take that total 24-hour figure and divide it by 24 to figure out your hourly rate. That's how many calories you burn in an hour of laying in bed. Now you need to figure out how to add your extra calorie burn from exercise to that number. A standard, generic approach for doing that involves the Metabolic Equivalents (METS) formula, which is the same formula that most on-line trackers and exercise machines rely on. Some scientists looked at a lot of different kinds of activities and assigned MET values to them based on values seen in large groups of people. Laying in bed has a MET level of 1, while (for example) moderate walking on a flat surface at 3 miles/hour has a MET value of 3.3, while running at a 6 minute mile pace might have a MET value of 7 (these aren't necessarily the actual MET values for these activities--just an illustration). This means that you'd be burning 3.3 times your resting metabolic rate while walking at a moderate pace, and 7 times your RMR while running at 10mph. So, for example, if person A had a resting metabolic rate of 2400, that would be 100 calories per hour; and that means Person A would be burning 300 calories per hour when doing an activity with a MET value of 3, or 700 calories per hour with an activity with a MET value of 7.
Here's a link to a Wikipedia article that explains all this in a little more detail, and also includes links to a Compendium of Physical Activities which gives the MET values usually assigned to many common exercises, activities, and intensity levels:
Now, here's how you can use all this to do a quick reality check when you see claims about how many calories/hour you're going to burn when doing a particular workout. I'll use myself as an example. As a 202 pound, 65 year old male who is 6'2" tall, the RMR calculator linked above tells me my resting metabolic rate is very close to 1800 calories for a 24 hour day, or 75/hour. So, for me to burn 1200 calories in one hour, I would have to be doing an activity with a MET value of 16 (16 x 75 = 1200). Not humanly impossible, exactly, but pretty close, at least for me. Typically, moderate intensity cardio has MET values in the 3-6 range, high intensity is 7-10, and competitive athletic competition might get you up into the 12-16 MET range. So, for me to burn 1200 calories in an hour, I'd need to be able, essentially, to give Michael Phelps a real run for his money in a full-hour, max-effort swimming race, or do whatever the equivalent amount of effort would be during a 60 minute kettlebell workout. I'll leave you to figure out how realistic that might be.
Obviously, your numbers will be different from this example, based on your age, gender, size and fitness level. But the real-life bottom line is that very few people can burn 1200 calories per hour with any kind of exercise that they can actually sustain for that length of time. For most of us, 600 calories per hour will be much closer to reality for the kind of sustained moderate to high intensity activity we can actually do for an hour. You can probably burn quite a few more calories per minute for short bursts of very high intensity work, life lifting heavy weights for a few minutes, or running very fast up a shortish hill. But you may not be able to sustain that level of effort for an hour, which is what it would take to burn 1200 calories in 60 minutes.
Unfortunately, estimating exercise calorie burn is probably never going to be an exact science, unless and until someone finds a practical way to actually measure it in the moment without requiring that we be hitched up to a machine in a laboratory. In the meantime, I'd be pretty suspicious of any estimate you get from a machine, calculator, or equipment/workout salesperson that says you're burning much more than 600-800 with 60 minutes of effort, unless you're a very well trained athlete working very hard for the full 60 minutes.
Hope this helps.
"All your life, you have just been waiting for this moment to arise."
(Lennon & McCartney, "Blackbird")
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