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HRMs cannot count calories during strength training

Since this keeps coming up, I decided I am going to write this once and then just repost it.

I know that we are all concerned with counting calories, and we all want to know our exercise calories. Unfortunately, there is no consistent way to calculate actual calories burned during strength training. I also understand that, human nature being what it is, we tend to place great faith in fixed numbers--there is something very authoritative and definitive about that number on our wrists that makes it hard to resist--even in the face of all scientific facts to the contrary. (Remember--for a long time people had trouble accepting that the earth was round).

It's just something you are going to have to live with. Heart rate monitors CANNOT count calories burned during strength training.

The most commonly accepted method for measuring the calories burned for a particular activity is to measure oxygen uptake (VO2).

During *steady-state*, *aerobic* exercise, the TCA cycle is the primary means of producing energy, and oxygen is utilized at a relatively consistent rate depending on the intensity of the exercise. There is an observable and reproducible relationship between heart rate and oxygen uptake. If we have some individual data--resting heart rate, maximum heart rate, VO2 max, weight--it is possible to make reasonably accurate estimates of caloric expenditure based on the percentage of HRmax or percentage of HRreserve at which someone is working.

From the other perspective, basic exercise activities that have a common movement--walking, running, cycling, stairclimbing--have been extensively studied and equations to predict energy cost have been developed that are applicable to most of the general population. Cross trainers/ellipticals are the exception since they do not have a common movement design.

It is under these conditions and with these types of activities that calorie estimating equations and heart rate monitor estimations are the most accurate--exercises and exercise movements that are aerobic in nature and that are performed at intensities between 40% of VO2 max and the lactate threshold.

If an activity does not meet these criteria, then prediction equations and heart rate monitors become less accurate.

When it comes to strength training, they are not accurate at all.

There is a mistaken belief among many people--repeated even by many "experts" on bodybuilding websites--that ANY increase in heart rate reflects aerobic conditioning and an increase in caloric expenditure. This is not true. The primary reason is that the increase in heart rate that occurs with strength training results from a different physiologic mechanism than it does during aerobic exercise.

The increased heart rate that occurs with aerobic exercise is the result of the need for increased cardiac output--the heart must pump more blood to meet the energy demand of the activity. Heart rate increases because of a VOLUME load.

The increased heart rate that occurs with strength training is the result of changes in intrathoracic pressure and an increase in afterload stress. There is no corresponding increase in cardiac output, and thus only a modest increase in oxygen uptake. Heart rate increases because of a PRESSURE load.

So, unlike aerobic exercise, the increased heart rate during strength training DOES NOT reflect either an increase in oxygen uptake or a significant increase in caloric expenditure. Moving quickly from machine to machine to keep the heart rate elevated does not change this fact. It is still a pressure load, not a volume load.

Does this mean that strength training is a less useful activity for weight loss, or that it does not contribute to maintaining a calorie deficit? Of course not. Strength training is a critical part of a weight loss program. Strength training may only have a modest observable calorie burn--actually it's more like a simmer--but it can contribute to an overall calorie deficit in other ways--a modest "afterburn", conservation of lean muscle mass, the metabolic effects of more rapid protein turnover, for example. But the effects of strength training are not general in nature--they are very specific to the individual, and they are affected by so many different variables, it is impossible to formulate an equation or prediction table that is applicable to the general population. Since the focus of this article is strength training and heart rate monitors, I will not go into detail about the many benefits of strength training and weight loss.

So far I have been discussing "traditional" strength training programs--i.e. structured routines consisting of "sets" and "reps" at relatively heavy intensities--up to 10RM-12RM.

What about "circuit training"? There are two basic types of circuit training--One features alternating cardio and strength stations; the exerciser performs one set at a strength station, followed by a 1-3 min cardio interval, and alternates. The second type features a circuit of strength machines only. Traditionally, circuit training routines feature higher-reps, higher speed of movement and lower resistance levels--often 40% of 1 RM. Because of the lower resistance (or in the case of the first type, the inclusion of cardio intervals), these types of circuit training will involve more of a dynamic volume load, and thus a higher caloric burn. Using HRMs is still problematic, however, because the inclusion of upper-body lifting movements and the higher resistance (compared to aerobic exercise) means that HRMs will most likely OVERESTIMATE caloric expenditure--by as much as 30%-35%. For example, a heart rate of 85% of max that would normally reflect a VO2 of 70% of max might reflect a VO2 of only 51% of VO2 max during circuit training.

Again, in this article, I am not evaluating different training methods, just discussing the accuracy of HRM calorie estimates from these types of activities. 

Does this mean that heart rate monitors are not useful? Not at all. For a number of aerobic activities--most ellipticals, spin classes, running outdoors, other aerobic-style classes--they are still the best option for estimating calories. And they can be used for circuit training and some mixed classes or cross fit workouts--both as a more vague estimate of calories burned, but also for workout-to-workout comparisons. And for many people, by the time you get to the point where you can and need to start doing more intense lifting and circuit workouts (e.g. tabata, crossfit), calories burned during a workout is less relevant anyhow.

41 votes + -

16 comments:

whyflysouth wrote 92 months ago:
I almost don't want to believe you just b/c I want it all to be clear and simple but you've got a convincing argument. In our desire to make everything predictable and calculatable we use these hrms to give us a daily reassurance that we are on track, that by day X we will be at our goal. Thanks for the jolt of reality there.
dudleyvic wrote 83 months ago:
Wow...you don't know how perfect the timing of your article is to me. I had just gotten a hrm and was extremely disappointed that my calorie burn during a strength training class was not higher. As of today I was thinking of quiting class and then I came home from work and there is your article. I needed to be reminded that the benefits of the class out weigh the small number on my hrm. Thank you.
tmogs wrote 83 months ago:
Nice explaining. Thanks it helps alot!
rescuepete wrote 83 months ago:
Dude, you are so on your game with these explanations. You always speak as the voice of reason. So, my question is, what is a person to do as far as working on a site like MFP which is calorie-reestrictive in the diet plan? We're encouraged to track our calorie output to gauge more accurately how much to put back in. However strength training is clearly delineated from cardio on MFP's exercise tab. Is it not worth it at all to estimate any kind of cardio calorie burn from strength training, or just to put in something entirely modest? For example 20-30 minutes of strength training is maybe 60-100 calories burned?
Azdak wrote 83 months ago:
rescuepete: I think that depends on your overall plan and partly how many calories you are burning during cardio. Me, I never count anything but aerobic exercise--unless the only thing I do on a given day is strength training or a metabolic circuit; then I throw in a few on my log as a "marker" that I did something. But I burn 800-1100 calories and hour doing cardio, so the extra 200 or so lifting weights doesn't seem like a big deal. Others might want to include more as a motivation.
The problem is that there is no standard way to estimate strength training calories--too many variables. For a standard lifting routine--e.g. 2-3 sets, 8-12 reps, rest 1-2 min between sets, the research I have seen suggests that you directly burn about 3 calories per Kg of body weight per hour. The real difference comes in the time between strength workouts. For most people, it's not so much the increase in muscle mass that makes a difference--increasing mass is a slow process and most people can't increase that much--it's the dynamic process of protein turnover that occurs due to the hormonal response to the resistance. So, strength training is crucial for weight loss, IMO--it's just hard to quantify the calories.
myukniewicz wrote 83 months ago:
great explanation. thank you for posting this.
jacksonpt wrote 68 months ago:
Is respiration rate a better indicator of increased caloric burn, or am I trying to hard to make this about the numbers?
MoveTheMountain wrote 64 months ago:
The comment above is the one I'm curious about... If I'm breathing like a fiend, and my heart rate is through the roof, doesn't that signify that my body is working harder, and therefore burning more calories? I would agree with the argument above if my breathing were normal, and it was just my HR that was up, but when I do some of my routines, my breathing is way way up too.
bsharrah wrote 64 months ago:
Your body is working harder, and burning calories. It is just that a HRM can not accurately measure the amount burned.
amr1rizk wrote 55 months ago:
What do you mean by pressure and volume load ???
odusgolp wrote 43 months ago:
My head hurts...
princessbride42 wrote 43 months ago:
I am still lost. My understanding about a heart rate monitor is that it measures my heart rate, which is turning oxygen into making my body move. Therefore if I were wearing a HRM all day long, it would tell me how many calories I "burned" during that day. If my heart rate is 160 throughout a workout, how can it matter what I'm doing during the workout? I'm not doing extremely heavy lifting anyways, it's TRX training, but if I can't get an accurate count by wearing my HRM all day, how am I supposed to know what I'm expending?
Anonymous wrote 37 months ago:
I am a professional trainer certified by The American College of Sports Medicine. The addition to this logical explanation is that increased muscle mass increases a persons basal metabolic rate . In other words it takes more energy for your body to maintain muscle mass and you burn more energy or calories if you will when you are inactive. Strength training has many benifits in addition . It maintains and increases bone density, improves cardiac out put and more.
Hank Miller

Anonymous wrote 28 months ago:
I am a physician and I have to commend you on the above explanation. While it is written for a lay person to understand, your explanation touches very nicely on the complicated metabolic intricacies of determining workload. The important thing for everyone to remember is that metabolism is the NET result of AT LEAST several energy systems operating (or not operating) at the same time. To think that ONE parameter, such as HR, V02, distance, speed, age or body temperature can serve as the single best determinant of metabolic rate is silly. I can, however, recommend that serious athletes perform some form of metabolic testing to get some baseline understanding of their metabolic parameters but take it with a grain of salt. Again, these are just numbers, but when evaluated all together, age, VO2, HR, etc can help you train for efficiently.
Anonymous wrote 21 months ago:
All very interesting. I am a 65 year young runner of the last 22 years. Last year I still finished six out of eight attempts of 100-mile trail races, so I still take my running addiction seriously. I use a HRM and its associated on-line training load calculator, which combines its estimate of my maximum heart rate, my age, weight and recent training history and plots where on a chart (green good to train, yellow avoid intense training and red don't train) where my most recent training places me. For me, this chart is a fairly accurate measure of my recovery status relative to how I feel during effort the next day and my current day's effort. For the past year I started resistance training, as I had only run for most of my past. Currently I am putting in 60-75 minutes of resistance work 3 days a week (upper body one day, legs the next and abs the next) with 3 days of varied cardio (rowing, biking, elliptical and stairs) in addition to 6-7 days of running. My resistance routines measure relatively low heart rate (65-95 bpm) and correspondingly low calorie expenditure (200-350 calories per session), while my running and other cardio averages 100-125 bpm and 500-800 calories per hour for 1-4 hour sessions. I assumed because I was not working as much of my body per exercise for resistance work that that was the reason my heart rate was lower, although I am breathing fairly hard during my resistance work, which is generally quick sets at less than maximal weight. I do notice as I get stronger, I can do them faster and at a higher heart rate for more sets and repetitions until I increase the weight and then I slow down again. I like to use the time to complete a rep/set combination and my average HR for that exercise as a measurement to compare week to week both as a measure of improvement and how potentially over trained I am from my recent past. When I feel strong and can do them faster and when I feel over trained they slow down.
Anonymous wrote 12 months ago:
I would like to learn more about this. Could you please cite some references?

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