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This is a very common and reasonable question. But it’s one that often gets an entirely unreasonable answer.
The numbers that get bandied about can be a bit… inflated. Burning calories is, after all, good business. This doesn’t mean that the fudging of numbers is intentional. Fitness professionals plot out the best case scenarios (and then perhaps round up again). Clients and customers go with it because they want to believe. How does one figure out what’s actually going on?
To understand things better, we’re going to make a pragmatic statement, discuss a few practical applications and explore a bit of exercise physiology.
A pragmatic statement:
It doesn’t matter.
Unless you’re an exercise physiology nerd, the details are probably a lot less important to you than whether your hard work is translating into fat-loss. Getting leaner? Great! Your stuff is working! Not getting leaner? Well, that’s more complicated. However, calories in vs. calories out is certainly a reasonable place to start. On a basic level, we know that there has to be some level of deficit for weight loss.
Two important details here:
1. Some level of deficit. More is not always better.
2. Counting calories (in or out) is not the only way to measure things.
A few practical applications:
Exercise can be measured by things like time, effort and frequency. For example, “I trained at a 7/10 effort for 40 minutes on Sunday and I did six 30-second sprints at 8.5/10 effort on Monday. I’m now on track to train five days a week; an increase from four days a week last month.”
Food can be measured by things like serving size estimates, fullness and frequency. For example, “I prepared a palm-sized piece of steak with a fist-sized serving of rice and two fists worth of salad for lunch. I felt completely full afterwards so I’ll reduce the amount of rice and steak by 10% for lunches going forward. The veggie quantity will remain the same because I hate veggies and want to see their species eradicated.”
Neither example required precise measurements; only consistency. It’s achievable and practical to fine-tune your efforts until you’re seeing forward movement. It’s also a lot more reasonable for most people as part of a long-term strategy. Consistency of measurement is a lot more important than accuracy. Especially since the specific numbers are so hard to pin down for anyone not regularly hooked up to a metabolic cart.
A bit of exercise physiology (and maybe a clearer picture of metabolism):
Want to know how caloric expenditure is actually measured by researchers? It’s not, really. Calories are estimated after the fact.
To begin with, researchers measure Metabolic Equivalents of Tasks (METs). A MET is a bit more complicated than a calorie. It represents a fixed amount of oxygen per kilo of body weight per minute.
The harder you work, the more oxygen you need. One MET is your body at rest. This will not be on the exam. However, there is a detail that you will want to remember: the multiplier here is bodyweight.
Per kilo per minute means that the heavier you are, the higher your (resting) metabolism. This is perhaps contrary to some expectations that a heavier person might have slower metabolism. There are several other factors at play in the metabolic equation but bodyweight (regardless of body composition) is the single biggest factor.
Once we know how many METs are required, we can estimate caloric expenditure a little more accurately.
A bunch of examples:
A 110 lb person at rest will theoretically consume 175ml of O2/minute. Now we can estimate how many calories this level of activity requires. The answer is about 0.8 Calories/minute. What if a 200 lb person is at rest? That number jumps to 1.5 Calories/minute.
You’re probably not super excited by these numbers. Bear in mind, however, that exercise can multiply that base rate by more than 20 times. For most people with a less extensive training background, a ballpark of 10 METs is practical. At 10 METs, the 110 lb person is expending about 8.3 Calories/minute and the 200 lb person is expending 15.2 Calories/minute.
Lets say that both of these individuals jog at a steady but vigorous pace requiring 10 METs for 45 minutes. What will than translate into?
At 110 lb: 375 Cal.
At 200 lb: 682 Cal.
This is equalizing for fitness levels, training experience, and a host of other factors. Even with all that in place, you can see that the numbers for two different people can vary incredibly. To throw out a universal number seems kind of crazy.
“I definitely burn more calories than that.”
Say, have you seen this video?
This is world champion and Olympic medalist Robert Förstemann consistently pumping out 700 watts for a little under two minutes before quietly finding a place to lay down. There are undoubtedly some efficiency losses in the “toaster room” but regardless of the numbers, there’s no doubt there aren’t very many human beings who can do what he did. Drink in those quads. Watch the incredible effort. Revel in the total calories burned. Wait, how many was that? Probably less than 75. And how repeatable is that effort? Not very.
I’ve heard of estimates as high as 1,200 calories thrown out from group class instructors. To be clear, Robert Förstemann would have to maintain the pace in that video for over 30 minutes to burn that amount of calories. Except that Robert Förstemann can’t maintain that pace. No human can maintain that pace.
For mortals (e.g. cyclists competitive at amateur levels), men can average around 3 w/kg and women at about 2.7 w/kg.
For a 45-minute class at maximum sustainable power for a recreational cyclist:
At 110 lb: 365–450 Cal.
At 200 lb 662–736 Cal.
These are still very high numbers. They’re based on going close to all-out for 45 minutes with no breaks and no slowing down.
“Ok, so how many calories am I burning?”
There are some links in the references that will help you determine what your caloric expenditure looks like based on weight and effort (with some activity equivalents). Then again, those details may not be important as long as you’ve got some way to measure progress.
The main takeaway here is not to blindly trust the numbers that someone gives you. Figure out what metrics are important to you, decide what’s easy to keep tabs on and go with that. Your progress will tell a tale that calories never can.