calories burned vs heart rate vs type of exercise

I think if I lift weights (bowflex) and keep my heart rate  in the 150-180 range for 45 minutes that it is equal to any other exercise that keeps me in the 150-180 heart rate range (like mountain biking).  If the heart rates are similar then I  should burn about the same amount of calories regardless of the type of exercise .......right???  Or am I missing something? 

Does anyone  agree or disagree???

Disagree.

Heart rate is only an indirect estimate of calories expended--and only under certain conditions.

The only accurate practical way to measure calories expended is to measure oxygen uptake--which is not practical for everyday use. During aerobic exercise, there is an association between heart rate and oxygen uptake. This is because the primary mechanism of increased oxygen uptake is cardiac output--i.e. the amount of blood pumped by the heart. The heart pumps faster, cardiac output is increased, oxygen uptake increases. During aerobic exercise, heart rate and oxygen uptake have a similar linear (more or less) response to increased workload. In simple terms, if a person is at X% of their HRmax, it can be assumed that they are at Y% of their VO2max, so if you have some idea of VO2 max, the calorie burn at that exercise heart rate can be estimated. 

However, that only holds true if the increase in heart rate is accompanied by an increase in oxygen uptake/cardiac output. There are conditions under which heart rate increases without an increase in VO2max or cardiac output--weight lifting, thermal stress, emotional stress, illness, cardiovascular drift, to name a few. Under these conditions, heart rate cannot be used to estimate calories burned.

So, to put it simply, 45 min on the bowflex is not equivalent to 45 min on a crosstrainer or running, even if both elicit an elevated heart rate.

Now, nothing in physiology is that simple. It's not like there's an on/off switch. As a rule, as the resistance of a movement goes down, the dynamic aerobic quality of the movement goes up (oxygen uptake). Untrained individuals will likely see a cardiovascular training effect with just about any activity that is of higher intensity--but with weight lifting only, the effect will be only modest and most likely plateau at a low level.

There is also the "afterburn" effect of intense aerobic activity, so if one is doing a HIIT-type cardio/strength circuit, there is some aerobic training taking place.

The type of exercise--arm or leg--can also have an effect, since upper body exercise a higher HR response relative to VO2 than lower body exercise.

One example: one study of a circuit training class showed that, while exercise heart rates were in the 70%-85% HRmax range, VO2 (oxygen uptake) ranged only 39%-51% of VO2max. During aerobic exercise, those heart rates would normally reflect 57%-75% of VO2max. If you were using a HRM for this type of workout, it would be off by 12%-30% just based on that alone. And the discrepancy is even greater with traditional weight training. A study in the 1980s showed that performing strength training on Nautilus machines at a 12-15RM workload did not result in any aerobic training effect after 12 weeks, even though heart rates remained elevated in the aerobic training zone during the workouts and there was no rest between stations.

So, again, the short answer is, No, they are not equivalent. There is a blending of aerobic and non-aerobic responses and training effects based on the type of activity, structure of the workout, and initial fitness level. As more people take up "hybrid" high-intensity cardio and strength workouts, determining what happens physiologically is becoming more important and should provide many thesis ideas for graduate students.

Well said azdac, I've been trying to caution people about using HRMs to count calories for non-aerobic activities but have not been able to explain it as well as you did.  I hope you don't mind if I quote you in the future as this topic comes up often.

Thank you so much for the detailed reply, I really appreciate it.

It is very educational........excellent!

Another question related to the subject:

Are the calorie counter estimates on mountain biking and weight lifting fairly accurate for guessing calorie burn levels assuming you are working hard and breathing hard and keeping the heart rate up in the 150-180 area for 45 minutes or more?

Original Post by keithooo:

Thank you so much for the detailed reply, I really appreciate it.

It is very educational........excellent!

Another question related to the subject:

Are the calorie counter estimates on mountain biking and weight lifting fairly accurate for guessing calorie burn levels assuming you are working hard and breathing hard and keeping the heart rate up in the 150-180 area for 45 minutes or more?

I don't really use calorie counter for that purpose. I don't count weight lifting calories at all because: a) the actual number is so low, it really counts more as "casual activity" and b) the benefits from strength training come after the workout and are not reliably quantifiable.

Don't know about mountain biking--there are issues using any calculator table for outside cycling since one can "rest" while going downhill, and terrain can vary from ride to ride. But if you notice that your HR is consistent in the range you mentioned, then it is probably OK--all these numbers are estimates anyhow.

 That is tantamount to finding out there is no Santa Claus.

Well, I'm not so sure that the Nautilus results are all that relevant to the discussion, while quantifying energy expenditure through strength training is tricky there's quite a bit of indication that it burns considerably more calories than previously reported.

 Endurance training will burn more calories regardless of course; continuous lower expenditure will beat intermittent high effort regardless just by virtue of being sustainable for a lot longer. Same thing with HIIT or IT vs. steady state, one hour of steady state will burn a lot more calories than half an hour of HIIT.

 Thing is, direct calorie burn during exercise is just about as irrelevant as substrate utilization is, it's the physiological adaptations in response to the training that's actually important when you're considering what sort of training is goal-appropriate for your specific goals in terms of body composition and sports performance, neh?

Wow....thats deep melkor. Thanks for the info. I love studying this stuff.

I feel like since I am only a month and a half  into this (213.6 now vs 230 at the start) with a goal of 195;

That any movement I do that keeps my heart rate in a 150-180  range for 40-60 minutes is gotta be helping some, How much?...I have no clue? When I work out I make a point to keep that heart rate up the whole time. I cross train with aerobics and lifting with an emphasis on aerobic, Once I reach my weight I plan to expand my lifting and strength training aspect. erica somebody did a post\thread on getting to 20 pull ups; seemed like a really challenging goal to attempt. Once the weight is off .....I'm hoping I'll make a dent in 20 pull ups?

I do have a shoulder issue (rotator cuff) that may stop my lifting\pull up aspirations?

Thanks again for the info, and please any one else that has thoughts on the subject(s) ......please reply.

I'm a nerd, I like nitpicking details - but for the vast majority of people everything boils down to "control calorie intake for weight loss, do some resistance training to preserve muscle mass, and add in endurance training of an intensity that's sustainable for the time you've got available".

Sometimes I get a bit too wordy when I wander off into the weeds of the details that really doesn't matter all that much to anyone who isn't prone to nerdgasms or are actually competing in a sport where any of this actually matters.

 For people who have limited training time doing high-intensity cardio is good, for people who have more than a few hours a week to train intensity is a lot less useful than building a cardiovascular fitness base to work from with slow and steady work.

I really believe that you need to think in terms of training for fitness, rather than focusing everything on weight loss. You might make some adjustments to burn more calories, but, overall, we should be thinking long-term.

Training for fitness means all aspects of your program. A balanced program includes endurance training, tempo training and interval training. The degree to which you push all 3 depends on one's abilities, health history, fitness level, etc, but the proportion should be there.

I also believe in the importance of periodization. If one looks at a progress graph (e.g. improvements in fitness performance), while overall progress make look linear, week to week intensity/volume is not--it is more of a sawtooth pattern where more intense weeks are alternated with lighter weeks, harder cycles with lighter cycles, etc. I have found that changing things up every two weeks has worked really well. Sometimes it's hard when you have hit a new high point to back down the next 2 weeks and build back up, but I always end up at a new high point and that it the whole idea.

I have been doing this for 3-4 months now and it is working well. My endurance weeks are starting to feel like "vacations" and it's a nice physical and mental break. I keep cardio intensity at 55%-65%, resistance levels to 12RM and also switch to alternate exercises--bands, balls, body work--I even try a workout class sometimes.

thanks for the info, I got some useful tips

Its more of a journey than a sprint.

Keitho