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Trying to estimate TDEE and don't really know how many calories are burned during 5x5 strength workouts, or equivalent weightlifting time spent in the gym. Want to make sure I am eating enough, and also not too much. Is there any good estimate out there?

FWIW, I am a 33 y.o. female who just started weightlifting 6 months ago, DEXA scan of 30% BF, RMR test of 1450kcal, trying to lose fat. Was previously a cardio addict with an eating disorder so I was used to thinking that to reach my goals I needed to work out longer and eat even less, and the concept of eating more and less gym time to lose fat is scary to say the least.

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Well, I guess if you want to know how much energy each squat, deadlift, and bench rep, you would just calculate how much work you did.

Work = force x distance

Or

Joules = Newtons lift x distance to lift.

Where 1 human calorie (kilocalorie) = 4184 joules.

To calculate Newtons, we calculate the mass (kg) by the force of gravity on Earth (9.81 m/s).

So if you're doing 5x5 squats with 50 kg weight which is a total of 25 reps. Let's say your range of motion is 1 meter, so you would have lifted it 25 total meters.

50 kg x 9.81 = 490.5 N

490.5 x 25 total meters = 12,262.5 joules.

12,262.5 joules / 4184 joules = 2.9 calories burned just squatting.

You can do the same for deadlift and bench press.

This is assuming optimal efficiency. A beginner may burn a little bit more than that because they're less efficient, but not enough to care. There is also the amount of calories burned standing and holding the weight between sets as well as burning in the decent. I would imagine this is negligible.

You'll burn more calories if you increase the weight. You'll burn less calories if your range of motion is shorter, and more if it's higher.

The caloric burn that strength programs do is not that much in when you're actually doing them. The real caloric burn is the increased TDEE after. Strength training (especially at the advanced stages) increases your overall EPOC for days after. It takes extra calories to recover from the workouts. The correct amount though is incalculable.

The old-school way of determining your TDEE (and really only way without expensive equipment) is to eat at a very strict level for one month. If your weight goes down, then this is below your TDEE. You can estimate it based on the amount of weight lost. If your weight goes up, then this is above your TDEE. And, of course, if it's the same, then you've found your TDEE.

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    +1 for the calculations. I was in the middle of writing the same stuff myself, but now I don't need to :) – Alec May 4 '18 at 18:33
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    If I'm not mistaken, your math is wrong. You are assuming kgs measure force - lbs do, but joules are N m, not kg m, right? – Stephen S May 4 '18 at 20:48
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    @StephenS You're right. That should be in Newtons. – DeeV May 4 '18 at 20:50
  • This is incorrect, as the energy calculated should be that to lift 50kg through 25 metres, not to lift 1,250kg through 25 metres. You're double-counting the 25 here. The lower bound on the energy expended is 2.9kcal. As described below, the total will be higher due to the body not being perfectly efficient and also lowering the body itself when squatting. – Chris Cundy May 4 '18 at 23:17
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    "This is assuming optimal efficiency." That is not a reasonable assumption. The human body is not even close to to being 100% efficient at converting food energy into muscular work. In fact, it's much closer to 0% than 100%! – David Scarlett May 5 '18 at 10:32
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In addition to @DeeV's fine answer, since your stated goal is to lose bodyfat, consider simply not counting your resistance-training energy expenditure. As you can see, the actual energy expenditure directly attributable to resistance training appears to be negligible anyway. At worst, this will increase your caloric deficit slightly.

You might consider Death by Prowler; that is, using High-Intensity Interval Training (HIIT) to stimulate fatty acid oxidation. See the section near "130-150 bpm for a 30yr old" in the hyperlinked article for further information.

  • +1. The prowler is an amazing heartrate accelerator, and thus a good fat-burner. – Alec May 4 '18 at 18:43
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I was in the middle of writing pretty much the same calculation that @DeeV did, so I'll skip that, and supplement his answer with some additional information instead.

Weightlifting to burn fat?

The long and short of it is that calories burned during weight training is so negligible, that you shouldn't spend any time thinking about it.

You should choose your weight training program based on other factors. And in any case, like we've discussed earlier, you should be cycling between a bunch of different programs, so whichever ones you like, line them up, and do a few months of each.

The best ways to burn fat

...are done firstly by regulating your diet, and secondly by exercising in ways that increase your heartrate.

DeeV mentions that 25 reps of 50kg squatting (or any up-and-down exercise for that matter) burns 7.5 kcal.

If you do 7 sets of this (that is 7 sets of 25 reps at 50kg), you will have burned roughly 500 kcal. Or roughly a Snickers bar.

So if you're looking to burn fat, it takes you 5 seconds to forego the Snickers bar, but it would take you days to do 7sets * 25reps @ 50kg.

The mindset

If you're already pretty good at not eating candies and sweets, your bodyfat is getting to you from other sources, and losing fat is all about finding the weak spots in your dietary habits, and eliminating them.

Personally, I find it much easier to forego the "bad" foods when I do a simple calculation as demonstrated above, and realize just how big of a difference it makes to, say, have a glass of water rather than soda, or another helping of vegetables and one less of meat.

  • just FYI a snickers is 250kcal so I get to eat two of them ;) – Christine Urban May 4 '18 at 19:05
  • @ChristineUrban - Sorry, I just went by the number Google gave me. Probably talking about different sizes. – Alec May 4 '18 at 20:09
  • For what it's worth, I updated the calculations to use Newtons (force) instead of KG (mass) which increased the calories burned to about 70 for a set of 5 rather than 7 calories. – DeeV May 4 '18 at 20:55
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    Everything about this answer is wrong. Calories burned during weight training are not negligible, they are comparable to cardio exercise (ncbi.nlm.nih.gov/pubmed/25162652), and additionally, weight training increases metabolism for more than a day after training (ncbi.nlm.nih.gov/pubmed/11882927). Furthermore, your calculations are out by a factor of 10, and Deev's initial calculations, on which yours are based, are probably inaccurate by a factor of at least 20-30 because they don't take into account inefficiencies in converting food energy to mechanical work. – David Scarlett May 6 '18 at 9:43
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Use a total daily energy expenditure calculator to estimate how much energy you are burning through weight training and other activities. For example, this one provided by ExRx, which categorises weight training (including rest between sets) as "moderate" exercise, along with other activities including cycling and tennis. The actual energy required during a weight training workout will depend on your lean body mass and the duration of the training session.

That will give you a starting estimate, from which you can determine how many calories you should be eating per day. Then just weight yourself regularly, and every week, take the average of your weights during that week, to get a more stable weight value. If you weight is increasing or decreasing as desired, then your food intake is appropriate. If not, then your energy expenditure estimate was probably inaccurate, and you can fix that by adjusting your food intake - increasing it if you lose too much weight, or decreasing it if you gain too much weight.

Do not try to calculate how much energy you are burning in the gym by the mechanical work required to lift the weights. That will be uselessly inaccurate as the human body is so inefficient at converting food energy into mechanical work.

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