Accurate Measure of Exercise Calorie Expenditure
If you have run on a treadmill before, you know there are supplied calorie counters, and you may have heard that these calorie counters are inaccurate. It turns out they are extremely inaccurate, boasting a 30% inaccuracy in estimated calories . So, is there a way to get around this? Of course there is, but is there a way to get accurate calories from running on the treadmill that does not involve a team of physiologists measuring a variety of variables? Yes. In this article, we will discuss exactly how to determine caloric expenditure through exercise in a quick, dependable way.
VO2 is the measure by which those in the medical community assess, non-invasively, how the body uses oxygen . Without measuring every factor known to impact VO2, we can assess how well the body takes in, deposits, and distributes oxygen (lung capacity, heart function, oxygen blood extraction, etc) in a general sense. That general sense or idea is enough to calculate, with remarkable accuracy, several different measures; in this case, calories expended while running on a treadmill.
How is VO2 measured?
Good question! (I realize I asked the question myself, don’t judge)
VO2 is measured a variety of ways, from highly involved (being hooked up to a machine and told to exercise) to mere estimations (equations). Can you guess which one we will be using?
This is a representation of a metabolic cart. This is the most accurate representation of VO2, but is quite time and labor intensive.
How accurate are these equations?
While, admittedly, the equations are not as accurate as going through a maximal exercise test while being hooked up to a spirometer (breathing tube) and metabolic cart, surprisingly, they are still accurate enough for our purpose. These equations were developed by testing and finding a standard that applies to all that fall within certain parameters (discussed later). There is a +/- 7% intersubject variability (all other variables accounted for), which is forgivable considering the ease of establishing VO2 .
How do we use VO2 to get calories used during exercise?
This is a bridge piece that is important to understand, because without it, we are stuck. However, the estimated caloric expenditure is dependent on a constant of 5 calories used for every 1 liter of oxygen used .
Where did this number come from?
Well, this is based on the respiratory exchange ratio (RER); a numerical scale of energy substrate use based on intensity of movement. In simpler terms, it is a scale that explains the balance between carbohydrate and fat use. The more intense an exercise is, the more carbohydrates are used, the less intense, greater fat use . Along with that scale comes an estimated calorie utilization based on intensity of movement. So, again, as intensity increases, calories per liter of oxygen also increase (naturally, considering the greater the movement, the more energy needed to allow that movement to occur). So, the 5 calories per liter of oxygen is based on an RER of 1.0 (near the top of the intensity scale). As such, it is not perfectly accurate, but the lowest position of the intensity scale (rest) has been estimated to have a caloric expenditure of 4.69 calories per liter of oxygen . So, a slight overestimation by taking 5 calories per liter of oxygen as the standard will have little impact on a person trying to find their exercise caloric expenditure (which, would be closer to 5 calories per liter of oxygen anyway as exercise is always more intense than rest).
The Respiratory Exchange Ratio (RER) chart. As intensity increases, RER gets closer to 1.00. As RER gets closer to 1.00, the body shifts to a glycolitic state, favoring carbohydrate use over fat use. The higher the intensity, the more calories needed.
Understanding the Running Equation (>5 MPH)
Here we are, you are ready to find out exactly how many calories you expend during steady state exercise, and I am prepared to offer that answer to you. How?
Using this equation, for running :
Using this equation, for walking :
If you hate math like I do, have no fear, this is ridiculously easy to understand.
First, let us understand how this equation is set up and what it offers you (only covering running equation, as the walking equation follows the exact same rules, just with different numbers for each constant).
We’ve already been over this, but VO2 is the amount of oxygen your body uses to facilitate your existence, and by knowing oxygen consumption, we can figure out calories.
(0.2 x S) (Horizontal)
This is called the “horizontal” portion of the equation, because it covers the forward movement of exercise (as in walking, running on flat ground, etc). The .02 represents the amount of oxygen (.02 milliliters) needed to travel 1 meter per minute; it is a constant. The “S” represents speed. Speed is typically characterized in miles per hour (MPH) you are traveling, but for this equation, it is converted into a more precise measure, meters per minute. We will go over the specifics of this in a minute, just understand it conceptually – miles per hour is too broad, so a smaller movement distance (meters) with a smaller time unit (minutes) gives far better clarity and exactness.
(0.9 x S x G) (Vertical)
This is called the “vertical” portion of the equation, because it covers any possible movement in an upward direction (going up a hill, for example). Again, the .09 represents the amount of oxygen (.09 milliliters) needed to travel 1 meter per minute; it is also a constant. The “S” represents speed. Speed is again measured in meters per minute for exactness (see “horizontal” for clarification). Then, “G” represents gradation. Gradation takes into account the level of upward movement during exercise (for example, treadmills allow for added grade to increase difficulty). Now, a treadmill will offer a percent change, but we cannot use a percent in the equation so we will need to change it to a fractional grade, explained shortly.
Finally, there is a little 3.5 stuck at the end, and that simply represents the amount of oxygen you are intaking at rest – no movement, just being lazy. The entire equation put together will offer your gross VO2 consumption, and everything but the “rest” component offers your net VO2 consumption.
To be clear, for this equation to be accurate, a person should be moving at a true running pace which is identified as having one foot not in contact with the ground.This running equation can be used for speeds 3.7 MPH – 4.9 MPH, but the results will be less accurate.
Step by Step Calculation of Running/Walking Calories
This is applicable to running on a treadmill, running on a track, or running outside; however the latter is not as constant (as there are hills, down slopes, grass, broken sidewalks, wind resistance, and many more factors that skew the results slightly). That being said, there is an adjustment set below to offset some of these immeasurable confounding variables. Also, follow the exact same instructions for walking, but replace the running equation for the walking equation (found above).
You will need:
A. Weight (explained shortly)
B. Running Speed (you should know why already)
C. Grade of Treadmill (you should know why already)
D. Exercise Time (explained shortly)
I am a 240 lb person with a running speed of 6 MPH at a 3% grade and I exercise for 20 minutes.
Convert weight in pounds (lbs) to kilograms (kg) by dividing 2.2 into your weight in lbs.
Convert miles per hour (MPH) to meters per minute (m/min) by multiplying your speed in MPH by 26.8 (1 MPH is equivalent to 26.8 meters/min).
Grade of Treadmill
Convert percent grade (%) set on treadmill by dividing by 100 to get a fractional grade. Note: If you do not use a grade on the treadmill, place a “0” in for “G”; this will null the vertical portion of the equation. If running or walking outside, assume a 1% grade. There is some research that indicates this is sufficient to account for some, if not most, of the confounding variables discussed earlier between non-treadmill and treadmill exercise .
Exercise time is calculated in minutes. So, this can be left alone.
B. 160.8 m/min (S)
C. .03 fractional grade (G)
D. 20 minutes
What do we do with these? Plug some of them in.
Okay, so now we have the amount of oxygen consumed by a single kilogram (kg) of weight per minute. However, we weigh more than one kilogram (obvi!), so this is where we factor in our weight to calculate the exact amount of consumption for our total body.
This is the total consumption, weight factored in, for each minute of exercise at these variables (speed, grade). Now, because calories are measured in proportion to liters (L) of oxygen and not milliliters (mL), as we currently have it, we will quickly convert our milliliters to liters.
We now know our VO2 in liters and can apply the 5 calories used per 1 liter of oxygen consumed.
Finally, we know the amount of calories we use to fulfill this exercise intensity – for one minute. Now is where we factor in the number of minutes exercised.
DONE! We have effectively calculated calories used during exercise if exercise was maintained at the values we set for the time we determined.
There are, of course, several limitations in regards to this approach. Granted, these equations offer some degree of accuracy and reliability, but again are not as exact as going through the process of being hooked up to a metabolic cart and assessing via exercise. However, among these confounding factors are a few that can be managed to increase accuracy. Here is a list of limitations to the American College of Sports Medicine metabolic equations:
1. These equations are only applicable in steady state cardiovascular, aerobic exercise. So, in layman terms, steady pace (within +/- 5 beats per minute of the heart), without sudden slowdowns or bursts of speed .
2. Biomechanical efficiency is also a factor as not everyone exercises the exact same way (some move arms more than others, for example) .
3. These equations were determined in a controlled, standardized environment, yet exercise at a gym or outside does not offer standard conditions (such as a temperature between 68-70 degree Fahrenheit) .
4. Equipment should be accurately calibrated. This is something that can be controlled easily; make sure the treadmill is in good working order (belt isn’t sticking, for example), and the variables you used for the equation are the variables you type into the treadmill. This is more of an issue for outdoor exercise as there are too many factors to control .
5. 5. The equations provided do not account for everything. Some of it is highly studied estimations, and the equations account for the majority of measurable VO2, but still are not as exact as indirect calorimetry via metabolic cart .
Now you are fully prepared to calculate your energy use during steady state exercise running, walking via the treadmill or outside. Armed with this information, you can receive a more exact count of your exercise needs to achieve a certain caloric expenditure.
Treadmill calorie count is wildly inaccurate, but using the ACSM metabolic equations for walking and running, we can get a better account of energy expended. Knowing weight, speed, grade, and time spent exercising (with the correct units of measurement), we are better prepared to estimate VO2. Once VO2 has been estimated, we can learn our individual caloric expenditure with a manipulation of these four variables.
Writer: Nicolas Verhoeven
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(No specific link – sorry, gathered from lecture in EXSS 4806 at East Carolina University)
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