Physics of my exercising - run vs walk
December 26, 2023 7:36 PM Subscribe
I'm 65Kg. I can run 2km in 15 minutes or I can walk 10km in 2 hrs. Which of these activities burns up more calories?
Walking by far due to the extra time/distance. The exact numbers vary, but generally running will burn 30-50% more calories than walking the same distance.
posted by Eyelash at 7:47 PM on December 26, 2023 [2 favorites]
posted by Eyelash at 7:47 PM on December 26, 2023 [2 favorites]
The basic physics of this is a matter of energy vs power. It's natural to assume that running inherently burns substantially "more calories" than walking because running makes us hotter and sweatier, but hotness and sweatiness reflects power dissipation while calories are a measure of energy i.e. total work done.
The thing that links power and energy is time: the energy required to achieve some specified change in the state of things (heating a pot of water from room temperature to boiling point, say, or charging up a phone, or moving a human body across 5km of terrain) is equal to the power applied to that task multiplied by the time over which that power is applied.
The SI unit for power is the watt, and the SI unit for energy is the joule: a joule is one watt-second. Apply one watt for two seconds, or two watts for one second, and you've expended two joules.
Expressing power in other units is often more convenient: a kilowatt is 1000 watts, a megawatt is a million watts and so on. Non-metric units are weirder, but all of them are just scalings of a watt: a horsepower is roughly 3/4 of a kilowatt except when it isn't, but even when it isn't, it's only a scaling anomaly rather than a different kind of thing.
Likewise, energy is often quoted in kilojoules (1000 joules), kilowatt-hours (1000 watts applied for 3600 seconds = 3.6 megajoules), BTUs (roughly a kilojoule) or calories (a calorie can mean either 4.2 joules or 4.2 kilojoules depending on context; the one most often meant is the 4.2kJ kind).
Again, all these energy units are just scalings of a joule. What they are absolutely not is scalings of a watt, because energy and power are not interchangeable despite the best efforts of confused and ignorant journalists to convince the general public otherwise. Even less interchangeable are energy and the rate of change of power. Newspaper articles about energy bills that refer to "kilowatts per hour" are a particularly gears-grinding pet peeve of mine.
If we assume a spherical human of uniform density, moving that human over some specifed path through the terrain - a 5km jogging route, say - requires expending the same amount of energy, i.e. the same number of calories, regardless of whether the route is taken at walking or running pace: the greater power applied to the run is exactly compensated for by the greater time taken by the walk.
But humans are not spherical, and a run is a somewhat more efficient gait than walk for most people because it requires fewer impacts with the terrain as well as being more effective at recycling impact energy, so in practice any given route will usually burn more calories if walked rather than run, contrary to what Eyelash says.
Running for the same time as a walk will burn more calories (i.e. energy) than the walk, because although running is more efficient it does require more power. As can be expected from the increased energy expenditure, it will also cover more distance.
In the particular case put here, the walking route is five times the length of the running route and to a first approximation is therefore going to require roughly five times as much energy to complete, even though it takes eight times as long to do so. This is a clear enough difference that gait efficiency considerations aren't going to change things much.
posted by flabdablet at 12:00 AM on December 27, 2023 [16 favorites]
The thing that links power and energy is time: the energy required to achieve some specified change in the state of things (heating a pot of water from room temperature to boiling point, say, or charging up a phone, or moving a human body across 5km of terrain) is equal to the power applied to that task multiplied by the time over which that power is applied.
The SI unit for power is the watt, and the SI unit for energy is the joule: a joule is one watt-second. Apply one watt for two seconds, or two watts for one second, and you've expended two joules.
Expressing power in other units is often more convenient: a kilowatt is 1000 watts, a megawatt is a million watts and so on. Non-metric units are weirder, but all of them are just scalings of a watt: a horsepower is roughly 3/4 of a kilowatt except when it isn't, but even when it isn't, it's only a scaling anomaly rather than a different kind of thing.
Likewise, energy is often quoted in kilojoules (1000 joules), kilowatt-hours (1000 watts applied for 3600 seconds = 3.6 megajoules), BTUs (roughly a kilojoule) or calories (a calorie can mean either 4.2 joules or 4.2 kilojoules depending on context; the one most often meant is the 4.2kJ kind).
Again, all these energy units are just scalings of a joule. What they are absolutely not is scalings of a watt, because energy and power are not interchangeable despite the best efforts of confused and ignorant journalists to convince the general public otherwise. Even less interchangeable are energy and the rate of change of power. Newspaper articles about energy bills that refer to "kilowatts per hour" are a particularly gears-grinding pet peeve of mine.
If we assume a spherical human of uniform density, moving that human over some specifed path through the terrain - a 5km jogging route, say - requires expending the same amount of energy, i.e. the same number of calories, regardless of whether the route is taken at walking or running pace: the greater power applied to the run is exactly compensated for by the greater time taken by the walk.
But humans are not spherical, and a run is a somewhat more efficient gait than walk for most people because it requires fewer impacts with the terrain as well as being more effective at recycling impact energy, so in practice any given route will usually burn more calories if walked rather than run, contrary to what Eyelash says.
Running for the same time as a walk will burn more calories (i.e. energy) than the walk, because although running is more efficient it does require more power. As can be expected from the increased energy expenditure, it will also cover more distance.
In the particular case put here, the walking route is five times the length of the running route and to a first approximation is therefore going to require roughly five times as much energy to complete, even though it takes eight times as long to do so. This is a clear enough difference that gait efficiency considerations aren't going to change things much.
posted by flabdablet at 12:00 AM on December 27, 2023 [16 favorites]
If the goal is to burn more (or less) calories, also consider what you will do with the remaining hour-and-forty-five-minutes of not running.
posted by demi-octopus at 1:14 AM on December 27, 2023 [7 favorites]
posted by demi-octopus at 1:14 AM on December 27, 2023 [7 favorites]
Another factor to consider: running is harder on knees and ankles, so most people can't safely run every day, and need to take one or more rest days every week.
Whereas most people can safely walk every day.
posted by chariot pulled by cassowaries at 4:23 AM on December 27, 2023 [2 favorites]
Whereas most people can safely walk every day.
posted by chariot pulled by cassowaries at 4:23 AM on December 27, 2023 [2 favorites]
I’ll suggest that it doesn’t even matter to compare a single session of exercise (as far as health benefits go). It’s doing something regularly over the long haul. Devoting 15 minutes a day seems very plausible. Devoting 2 hours a day wouldn’t be realistic for most people. Doing 15 minutes of running or 30 minutes of walking every other day would burn about equal calories as walking 2 hours once a week, but health-wise I think you’ll feel more benefits from the shorter more frequent exercise sessions. I think your best bet would be some combination of running and walking, as many days as you can work into your schedule.
posted by Kriesa at 4:27 AM on December 27, 2023 [2 favorites]
posted by Kriesa at 4:27 AM on December 27, 2023 [2 favorites]
the walking route is five times the length of the running route and to a first approximation is therefore going to require roughly five times as much energy to complete, even though it takes eight times as long to do so.
This. The amount of calories used is almost directly proportional to the distance traveled . See the figure here. It's not perfectly proportional because of slight efficiency differences. I could roll a thumb. Is that traveling 1 mile on a flat surface for the average person burns roughly 100 calories, regardless of how you do it
posted by Mr.Know-it-some at 7:09 AM on December 27, 2023 [2 favorites]
This. The amount of calories used is almost directly proportional to the distance traveled . See the figure here. It's not perfectly proportional because of slight efficiency differences. I could roll a thumb. Is that traveling 1 mile on a flat surface for the average person burns roughly 100 calories, regardless of how you do it
posted by Mr.Know-it-some at 7:09 AM on December 27, 2023 [2 favorites]
It's not clear if the OP was asking this as a physics curiosity, or asking for purposes of an exercise plan, but from the very first answer above ...
Of course you may care about things other than calories burned - eg, the cardio workout from running faster...
As others have already pointed out, exercise isn't just about energy burned, rather fitness. I think there's too much focus on calories, and not enough on a variety of exercise -- intensity, length, methods, etc.
I always remembered the minimum cardio workout (e.g. running) to be 20 minutes -- you needed to get your heart rate up for 20 minutes to trigger the fitness benefits of a minimal cardio workout. Now I can't confirm that with a few minutes of googling, so perhaps that's apocryphal or no longer valid. The AHA says 150 minutes of moderate exercise or 75 minutes of more intense exercise per week, and doesn't seem to say anything about the length of individual spurts.
FYI, flabdablet's reference above to a spherical human is riffing off an old physics joke.
EDIT: Careful with that voice dictation, Eugene, you could roll a thumb.
posted by intermod at 7:18 AM on December 27, 2023 [1 favorite]
Of course you may care about things other than calories burned - eg, the cardio workout from running faster...
As others have already pointed out, exercise isn't just about energy burned, rather fitness. I think there's too much focus on calories, and not enough on a variety of exercise -- intensity, length, methods, etc.
I always remembered the minimum cardio workout (e.g. running) to be 20 minutes -- you needed to get your heart rate up for 20 minutes to trigger the fitness benefits of a minimal cardio workout. Now I can't confirm that with a few minutes of googling, so perhaps that's apocryphal or no longer valid. The AHA says 150 minutes of moderate exercise or 75 minutes of more intense exercise per week, and doesn't seem to say anything about the length of individual spurts.
FYI, flabdablet's reference above to a spherical human is riffing off an old physics joke.
EDIT: Careful with that voice dictation, Eugene, you could roll a thumb.
posted by intermod at 7:18 AM on December 27, 2023 [1 favorite]
Depends what kind of "running" too.
Look up Slow Jogging (keywords Tanaka, niko niko) and that whole ethos.
Run slow, burn calories, avoid injury.
posted by KMH at 11:46 AM on December 27, 2023
Look up Slow Jogging (keywords Tanaka, niko niko) and that whole ethos.
Run slow, burn calories, avoid injury.
posted by KMH at 11:46 AM on December 27, 2023
As some of the answers have already mentioned: walking 10km, by far.
And as others have mentioned, you can think of the caloric expenditure of running/walking as roughly proportional to the total distance. It's true that walking (at typical walking speeds) is more efficient in terms of km/Cal, but that effect is more like 50%, not 400%.
However—assuming that you're considering an exercise program—keep in mind that an effective program will increase your capabilities over time. So there's likely to be a trade-off between your caloric expenditure today and your cumulative expenditure over a year. Imagine comfortably running, say, 60km a week at an average pace of 6min/km.
If you're interested in this type of thing, a good place to get started is r/running's "Order of Operations." If you want to go a bit deeper into the weeds, grab a good book with training plans, like Daniels' Running Formula or Pfitzinger's Faster Road Racing.
posted by neal at 7:19 PM on December 27, 2023 [1 favorite]
And as others have mentioned, you can think of the caloric expenditure of running/walking as roughly proportional to the total distance. It's true that walking (at typical walking speeds) is more efficient in terms of km/Cal, but that effect is more like 50%, not 400%.
However—assuming that you're considering an exercise program—keep in mind that an effective program will increase your capabilities over time. So there's likely to be a trade-off between your caloric expenditure today and your cumulative expenditure over a year. Imagine comfortably running, say, 60km a week at an average pace of 6min/km.
If you're interested in this type of thing, a good place to get started is r/running's "Order of Operations." If you want to go a bit deeper into the weeds, grab a good book with training plans, like Daniels' Running Formula or Pfitzinger's Faster Road Racing.
posted by neal at 7:19 PM on December 27, 2023 [1 favorite]
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running 2km at 8 km/hr at 66kg is 134 calories
walking 10 km at 5 km.hr at 65 kg is 420 calories
Of course you may care about things other than calories burned - eg, the cardio workout from running faster...
posted by ManInSuit at 7:46 PM on December 26, 2023 [2 favorites]