This is not precisely a question of exercise physiology, but it might be related. Simply, if you go to the gym and warm up on one of the treadmills or other workout machines there, often there is a readout of “calories”. Is this essentially a random number, or does it has something to do with mechanical work performed?
Notoriously inaccurate. I think Consumer Reports said so, but I’ve seen it multiple times. Anyway, your energy use rate is going to differ from mine. (I know some’s going to jump in here to say “A calorie is a calorie!” but is isn’t; metabolism across people is variable).
Each machine calculates those differently, but it factors your weight (if you entered it), the machine settings, and some formula. There are obvious pressures to make that number as big as possible, and few to make it really accurate.
Some googling based on a Consumer Report for wearable fitness trackers (which, to their credit have a heart-rate tracker for some info your stationary devices lack) found the calorie counts quite inaccurate. This seems the “plain language” summary of the research done:
Key quote:
In contrast, none of the seven devices measured energy expenditure accurately, the study found. Even the most accurate device was off by an average of 27 percent. And the least accurate was off by 93 percent.
Now this was only a study of 60 people, and was again, wearables, but I’d argue that stationary devices seem likely to be no better, and if lacking a heart rate monitor, far worse.
The article’s link to the actual paper.
Anecdotally (having given the best FQ answer I can above), I wear a smartwatch with a heart rate monitor, and supporting apps that have my height and weight entered, to make it a bit more accurate, and I automatically discounted 20% of the reported calories burned as aspirational. Looks like that’s probably still far too optimistic.
Some of the machines where I usually go have a heart-rate monitor that sometimes works some of the time, but I did not get the impression that they weigh you.
Depending on the device, I would expect them to be more accurate than something just based on heart rate. An bike can measure resistance and RPMs and calculate the work that goes into the machine. Then you’d need to multiple some efficiency factor, but that’d be less variable person to person than heart-rate to calorie conversion.
Still not terrible accurate, but it’s not a random number. Like if I do the same elliptical with the for the same amount of time and same amount of effort I’ll get roughly the same calorie burned count each time. If I do the same effort for half as long I’ll get roughly half the calorie count. It’s going to be ~alpha*true_calorie_count where alpha varies between machine and person (and probably over time for a given person due to age, fitness level, weights, etc).
Watches are not going to be very good since they are mostly guessing based on heart rate and arm swings. But heart rate isn’t really a good indication of calorie expenditure. For instance, your heart rate goes sky high when you’re afraid, but you’re not burning a ton of calories at that time. Machines will more accurate and consistent since they are mechanical devices which can measure things like speed, resistance, incline, etc. that contribute to the actual level of exertion. But few machines will be 100% accurate for an individual. The equations they use to calculate calories burned are based on averages and guidelines. For instance, there are charts which say what an average calorie burn is based on running at X mph on flat ground for a person of weight Y. Treadmills will use equations like that with a fixed value for the weight of the person. Probably that will be some average weight for most people. Even if the number isn’t 100% accurate, it will give you a rough idea of the calories you burned during the workout.
One thing the calorie count is useful is to measure the amount of effort you expended during the workout. This isn’t so much an issue on treadmills where the machine is setting the pace, but it can be helpful on machines where you set the pace, such as bikes and ellipticals. On those machines, your pace may vary between fast and slow over the course of the workout. Not all 20-minute workouts will be the same since you can move faster or slower over the course of the workout. The calorie count at the end of the workout will help let you know how hard you worked out and help you be consistent. Rather than working out for a certain amount of time, try to have a calorie goal. If you move fast, you’ll hit that goal quickly. If you move slowly, you’ll have to work out longer.
I did find a web site with some numbers; e.g., “Running, 10 mph” is quantified with a coefficient of 14.8 while “Resistance (weight lifting – free weight, nautilus or universal-type), power lifting or body building, vigorous effort” is 6.0, etc. It is certainly plausible that some apparatus is simply pulling values from such a lookup table.
On bikes and ellipticals, it’s best to make sure you use the same machine each time. That is, if you want to compare one workout with the next. Different machines will have differing amounts of internal resistance, so some will take more work to get the same RPM and thus your calorie count will be lower for the same effort you put out.
I note that upright stationary bikes seem to be the least popular cardio machines. Since that’s what I do my main workout on, I usually have no problem getting the same machine.
One of the treadmill machines in my gym once told me my heart rate was over 220. I’m still here.
As for calorie counts, I find them too depressing: to realise that, however sweaty and knackered I’m feeling, I’ve only used up one chocolate biscuit …..
The number is not random, but especially on older machines it is often highly optimistic.
You can estimate calories in several ways. The scientific way is to measure VO2 max (or METS) on many people and chart calories versus belt speed and weight on normalized curves. You can also draw biomechanical drawings showing all the forces, but these have some individual variation. Least accurate might be just to measure changes in heart rate.
The machines in my gym seem to work on the basis of speed, combined with the level (of some sort of inbuilt resistance, I assume) and time. It usually tells me I’m doing (using? radiating?) about 11 calories a minute.
My (limited) understanding is that the latter is where the former comes from, and are adapted to the machine use case. Possibly fudged some for market purposes.
Thing is the error bar for how each individual fits into that normal curve distribution is likely quite large.
Sure, but as said the company might not care if it overestimates the number of calories burned by huge amounts. The machines ask for your weight; not your height, gender, build or athletic ability.
Trying to dig some it looks like the standard for estimation are some formulae developed by the American College of Sports Medicine (ACSM)
The process then converts from oxygen consumption estimated to calories.
But it’s been apparently established that the formula frequently overestimate energy expenditure. For example:
The analyses were performed with the SPSS package. The results showed that there was VO2 overestimation for both activities (p < 0.05)
Even the idea here, using the same machine
has the problem that you as a machine are varying in your efficiency. As you stick with it you will develop running (or biking, or whatever) economy and in reality burn fewer calories for the same distance/resistance. The machine won’t catch that.
It may be better yet to stick with rate of perceived exertion, the simple bit of how hard am I breathing, how well can I talk? Or a good heart rate monitor if you want to be a bit more tech focused. And plan your workouts varying by zone more than by calorie count.
But this is FQ, not IMHO! I’m thinking the readout is based on the formulae. Not 100% sure but pretty sure.
The following rant does not address the thread topic directly and might be ignored. The readout is probably based on a formula, but these have probably improved slightly with research.
People who want to lose weight naturally focus on calories. But it is so hard to change your body points that Weight Watching type groups never publish their long term success rates. Turns out it is not usually true the indigenous fellow gathering food all day burns many more calories than anyone else. The new drugs absolutely make a difference if you stay on them, but better for many to strength train and improve composition. Treadmills are overused; you can burn many more calories on a climbing/rope pulling machine where the calculations are easier.
A fun article specific to ellipticals and their readouts -
Based on this study, one could estimate the machines overestimate caloric expenditure by about 130 calories during a steady-state bout of moderate exercise lasting 30 min, including warm-up and cool-down. Interestingly the overestimation was not significantly different for males (114.9 ± 31.77 C) versus females (137.4 ± 32.31 C), though the difference does tend to be greater for females. The discrepancy also increases by about 25 C for each 5 min block of steady-state moderate exercise for females compared to males. The results of this study support previous studies that found cardiovascular equipment overestimated caloric expenditure [5,6]. The finding that there was not a statistical difference between the discrepancy for caloric expenditure based on gender is similar to the findings by Erdogan and associates [6], but differed from Moyna et al. [7] who found a significant difference based on gender.
It seems some of the formulae used are proprietary. FWIW.
Also interesting the defaults if specifics are not entered vary but
When participant information is not entered, the Precor brand of elliptical machines uses default user characteristics of 150 lbs, 35 year old, and male to calculate caloric expenditure for most models, with models having a P80 console using a weight of 170 lbs
I’m curious and frankly highly skeptical about that claim. Running, be it on a treadmill or outside, is a very effective calorie burner, and extremely effective at optimizing one’s VO2max, which correlates well with healthspan. A machine that is much more upper body focused seems very unlikely to burn or accomplish as much.
Ironic choice of wording, there, since the accurate measures of Calorie consumption are, in fact, based on respiration.
Also, you burn Calories at some rate just by existing. I wonder if these machines (purport to) tell you your entire rate of Calorie consumption, or just the amount over baseline?
Indeed. This point is not as well known as it should be. The study below compared energy usage among several different groups: from Hadza hunter-gatherers, who spend much of their waking hours hunting and running down game, to American couch potatoes who get little physical exercise. Daily energy expenditure was measured by the “double labeled water method”, which uses isotopically enriched water, said to be the gold standard for measuring calories burned. The difference in caloric expenditure between the most active and least active groups was small, about 200 calories per day. The conclusion is that body weight is dependent almost entirely on food intake, and very little on exercise level. As the saying goes, “you can’t outrun a bad diet”.