Calories burned lifting weights

[julie1013]

I have a Fitbit Charge HR, and I manually enter the amount of time I spend lifting weights. When it calculates the calories, does it take into account the fact that people (at least should) take breaks between sets, or does it assume, for example, that if I put in 60 minutes that I'm constantly lifting for 60 minutes? The reality is, of course, that I do a set, take a 45-second break, and then do another set, and so forth.

Thanks

J

[MrG6ray]

If you have a Charge HR you shouldn't need to manually enter any exercise.  It automatically detects the increase in your heart rate and works out your calorie burn from that.  So whether your squating, resting, biceps, resting, triceps, etc. the Charge HR is registering it all.

[Dominique]

First of all, it is important to realize the main purpose of weight lifting is to gain strength and/or add muscle mass (or preserve existing muscle/strength), not so much burn calories. Although you will burn more calories lifting weights than sitting in your couch watching TV, you will burn less compared to performing an aerobic activity during the same period of time (for instance, one hour of brisk walking will most likely burn more calories than one hour of weight lifting).

Secondly, heart rate isn’t necessarily a good indicator of energy expenditure during weight lifting, so even a HR-enabled Fitbit may not give you accurate values for calories burned during your weight lifting session. IMO, your best bet would still be to log that activity as "weight lifting", whether on your device (if supported, such as with the Surge or Blaze), or via the Dashboard (with other models such as the One, the Flex, the Charge etc.).

I believe if you enter "weight lifting" as the activity in Fitbit, it will take into account the time spent actually lifting and the time spent resting between sets (as you said, there is no way you could keep lifting weights for one hour without resting at all). Of course, since there’s only one generic activity ("weight lifting"), it doesn’t make any difference between training focused on hypertrophy (high number of reps with lower weights and shorter rest times) and training focused on power/strength (low number of reps with heavier weights and longer rest times).

Anyway, I wouldn’t be too worried about Fitbit under- or over-estimating your energy expenditure during weight lifting by 50-100 calories, since the main purpose of lifting weights is not burning calories.

[julie1013]

Thanks for your response. The reason I ask is because I want to make sure that my Fitbit is accurately alloting the number of calories I have left for the day (ie, making sure I haven't gone over its suggested limit). Yesterday I did the entire circuit of arm weight machines at the gym, plus the three abdominal/back weight machines. It took me 76 minutes and it said that I burned 395 calories. Do you think this is an overestimate? 

[MrG6ray]

It will never be 100% accurate, but it will give you a good idea of the impact on your day as a whole.

[Dominique]

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@julie1013 wrote:

It took me 76 minutes and it said that I burned 395 calories. Do you think this is an overestimate? 

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What you will burn in any given activity depends on your gender, age and size (weight/height). Knowing only your gender, it’s diffficult to say.

You could try to find the activity that would most closely match what you did from the Compendium referenced in this older post. Then, use the METs for that activity to calculate calories burned in 76 minutes and compare that to what Fitbit estimates (as @MrG6ray said, it’s an estimate anyway).

[Corney]

Calories are calculated by your heart rate, it assumes nothing.  If you lifted for 60 minutes without a rest your heart rate would stay higher than if you took breaks between sets.

[julie1013]

My age is 35, my height is 5' 1.25", my weight lately has fluctuated between 133 and 136.

[Dominique · Accepted solution]

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@julie1013 wrote:

My age is 35, my height is 5' 1.25", my weight lately has fluctuated between 133 and 136.

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OK, your BMR is then about 1245 (for instance, as per this calculator). This is 1245 / 1440 = 0.865 calories per minute (1 day = 24 hours, 1 hour = 60 minutes, thus 24 x 60 = 1440 minutes in a day).

The Compendium of Physical Activities I mentioned earlier gives the following MET values:

circuit training, moderate effort: 4.3 METs

circuit training, including kettlebells, some aerobic movement with minimal rest, general, vigorous intensity: 8.0 METs

At these MET levels, you would therefore burn (in 76 minutes):

circuit training, moderate effort: 4.3 x 0.865 x 76 = 283 calories

circuit training, vigorous intensity: 8.0 x 0.865 x 76 = 526 calories

The 395 calories reported by Fitbit would be right about in between these two values, in other words, at a credible level.

[julie1013]

Wow, thanks!

BTW I don't know what "moderate intensity" is exactly. I mean, it's definitely not vigorous what I do. They tell you to lift the weights on the machines slowly to get the most out of the training. My heart rate stays between 90-115ish when I lift weights, depending on the machine I'm on. Should I perhaps default to the lower end of what you gave me?

[Dominique]

Yes, moderate vs. vigorous, it can be subjective with some exercises which may include many different items (such as in the case of circuit training). Some activities like stationary bike are easier to quantify:

bicycling, stationary, general

bicycling, stationary, 30-50 watts, very light to light effort

bicycling, stationary, 51-89 watts, light-to-moderate effort

bicycling, stationary, 90-100 watts, moderate to vigorous effort

bicycling, stationary, 101-160 watts, vigorous effort

bicycling, stationary, 161-200 watts, vigorous effort

bicycling, stationary, 201-270 watts, very vigorous effort

[Dominique]

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@julie1013 wrote:

My heart rate stays between 90-115ish when I lift weights, depending on the machine I'm on.

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Don’t be obsessed with heart rates. They do not really apply to resistance training. The range you’re seing when lifting weights is pretty normal.

[Dominique]

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@Corney wrote:

Calories are calculated by your heart rate, it assumes nothing.  If you lifted for 60 minutes without a rest your heart rate would stay higher than if you took breaks between sets.

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HR is one of the elements Fitbit considers when estimating calories burned, but it’s definitely not the only one. To prove this, I made a small experiment: using my Fitbit Blaze, I performed two activities (duration: 3 minutes each) that I entered as "WEIGHTS" on the Blaze.

Activity #1: bench press bar loaded with 8 kg (total weight of bar: 16 kg). I performed 55 reps in total, at a constant pace, thus lifting a total of 55 x 16 = 880 kg (for the metric-challenged, that’s 1940 lbs).

Activity #2: comfortably sitting in my couch, I clapped my hands (again, at a constant pace) for 3 minutes.

Now, you would probably agree with me that bench pressing a total of 1940 lbs must have burned more calories than the hand clapping, right? Well, not according to my Blaze: according to it, activity #1 burned 6 calories, while activity #2 burned 16 calories, almost three times more!

Why is that? Well, Fitbit are pedometers at heart. They feature motions sensors, and these sensors (together with clever algorithms)  were used for estimating energy expenditure (calories burned) back when there were no HR monitoring capabilities on Fitbit trackers. And now that some Fitbits do feature HR, motion sensors are still used for estimating calories burned, together with HR, and probably even cleverer algorithms.

Bottom line: don’t believe that calories burned reported by Fitbit come solely from your HR.

[AlKwas]

Julie 1013 -  it sounds that you are working out at a gym.  Long time ago there was a workout called the  Bulgarian workout.  It changed the way I workout..  Basically you super-set two body parts that are not pre exhausted by the other.   Like working squats then go right to forearms back to squat  to forearm... you rest your quads while you are doing forearms, and rest forearm while doing squats and so on and so on.  Cuts your time with the weights dramatically.   I have a home gym in which this works awesome, at a gym this could be difficult tying up two stations.  I state this because this will maintain your heart rate up and spend less time resting.

[Jb27]

I disagree. You burn calories when you're repairing muscle too so you one hour of weightlifting is *likely to burn way more calories than an hour of brisk walking...

[WavyDavey]

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@Jb27 wrote:

I disagree. You burn calories when you're repairing muscle too so you one hour of weightlifting is *likely to burn way more calories than an hour of brisk walking...

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This is true (maybe not "way more"), but there's no reliable way to measure calorie expenditure on recovery factors. A person has to play with the calorie intake portion of the equation to find the numbers to keep them at maintenance weight (or whatever their goal is). For a lifter during a serious bulk phase, the calories burned estimation may be too low.

[Valendroth]

This statement is misleading/false:

Although you will burn more calories lifting weights than sitting in your couch watching TV, you will burn less compared to performing an aerobic activity during the same period of time (for instance, one hour of brisk walking will most likely burn more calories than one hour of weight lifting).

Aerobic exercise will burn calories quicker but resistance training will burn more calories over time. For example say you burn 200 calories on a walk. Once the walk is over so your body is done burning calories.  Now let's say you lift for an hour and burn 200 calories. Calories are an important ingredient in muscle hypertrophy.  So you may say, for example, burn another 300 over the next 3 days as your body rebuilds the broken down muscle.  This is why some weight lifters will eat 3k - 5k calories a day. Resistance training is way more effective at burning more calories it just does it slower than aerobics. If you don't have fat to burn then you have to stay in a caloric surplus to build muscle effectively because of the caloric requirements to do so.