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Work and exercise

whitefork

None of the above
whitefork
Joined
Aug 6, 2001
Messages
2,326
Is it true that walking 10 km burns the same number of calories as running 10km? I would suspect so, since the amount of work would be the same.

What's the relation between weight and calories burned? If a 60 Kg person runs 10km, how many more calories would he burn than a 50 Kg person?

For swimming, how does the displacement in water affect the quantity of work done? If you weigh 50kg and swim 1 km, how would you calculate the quantity of work?
 
I'm sure someone can give you the exact figures, but basically you are right about walking and running.

The same amout of work gets done, it just gets done faster..( when running)

As for the swimming, it could get pretty complicated, because you have to figure in the water resistance and this could be highly variable based on surface area exposed to the direction of travel etc.. I don't think the displacement actually matters when it comes to the work needed to move a particular body through the water.. Aside from the fact that the ammount of submersion would affect the amount of surface area in contact with the water.. i.e. it would take more energy to move a stick of wood sideways through the water than it would long-ways...
 
My wood is not usually sticking out when I swim, so we can eliminate that source of resistance.

If you compared the water temperature before and after - I suspect almost all the heat is lost to the water rather than the air... I wonder how it correlates to the calories expended by the swimmer.
 
Walking at a comfortable pace is usually more efficient than running at a comfortable pace. So if you just walked you would use up less energy than if you ran. But if you walk quickly it becomes less efficient so that you end up burning more energy.
 
It's easy to confuse the physics definition of "work" with the amount of energy used during exercise. Technically, if you ran a marathon at full speed, on a level course, NO work at all would've been expended (assuming you started and ended the race at rest). Same with walkling the course -- no work.
 
garys_2k said:
It's easy to confuse the physics definition of "work" with the amount of energy used during exercise. Technically, if you ran a marathon at full speed, on a level course, NO work at all would've been expended (assuming you started and ended the race at rest). Same with walkling the course -- no work.
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To move a body between point A and point B you have to do "work" as it's technically defined in physics, even if the ground is on level, because of the friction force you have to overcome. This force is dependant on the gravity force in the end. If you drag a body it's the friction force between its surface and the ground. If you walk or run, the force is between your shoes and the ground.

I agree with Jethro that the energy "burned" to go from point A to point B depends on the "efficiency" of the means to do it.

One thing is the amount of work needed to cover the distance, and another is the amount of energy used in doing the job. If we define "efficiency" as the ratio between the former and the latter, then walking is more efficient than running, because less energy is needed.

In conclusion, when we run, we end up "burning" more calories, because as it's a less efficient method, a lot of energy is lost in the form of heat, and that's why we sweat a lot more than when we simply walk.
 
Diogenes said:


Of course, the resistance offered by your wood, could well be negligible, in any event..:D
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oh man that was a low blow but damn funny!
 
whitefork said:
Is it true that walking 10 km burns the same number of calories as running 10km? I would suspect so, since the amount of work would be the same.
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In my (non-medical) opinion, yes and no. The calories burned by walking or running the distance may be the same, but running will increase your muscle mass in the long run, and more muscle mass means more calories burned. Also, your heart rate remains elevated longer after you stop running, so I can only imagine you continue to burn extra calories even after you're done.

What's the relation between weight and calories burned? If a 60 Kg person runs 10km, how many more calories would he burn than a 50 Kg person?
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The rule of thumb I've heard is that it scales linearly. A 75kg person will burn about 60 calories per kilometer, so a 100kg person should burn about 80 calories.

Jeremy
 
The various calorie charts I looked at show that the faster one's pace in running, the more calories burned for the same distance - confirming Jethro's remarks on efficiency of means by which the work is done.

Does anyone know about any measures of efficiency of motion, say time-motion studies, time-lapse photographs? Is there some general rule that the slower an action is performed, the more efficient it is? For cars, gas milage declines the faster you go, and for human beings, the calorie output increases with speed. A lower, and therefore faster, planetary orbit - probably decay more quickly than a higher and slower orbit.

Must we conclude that sloth = efficiency?
 
whitefork said:
For cars, gas milage declines the faster you go,
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For cars there is actually a peak efficiency at around 55 mph or so (IIRC). That's why (along with the losses in efficiency from stop and go traffic) fuel efficiency is lower for city travel rather than highway travel. So no.
 
whitefork said:
A lower, and therefore faster, planetary orbit - probably decays more quickly than a higher and slower orbit.
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Yes, but that is because tidal effects are the cause of the slowing and the tidal effects are greater for lower orbits.
 
Diogenes said:
As for the swimming, it could get pretty complicated, because you have to figure in the water resistance and this could be highly variable based on surface area exposed to the direction of travel etc.. I don't think the displacement actually matters when it comes to the work needed to move a particular body through the water.. Aside from the fact that the ammount of submersion would affect the amount of surface area in contact with the water.. i.e. it would take more energy to move a stick of wood sideways through the water than it would long-ways...
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Alas, its quite a lot more complicated than this. The force of fluid (ie water or air) resistance varies in an extremely complex way with the speed, shape, size, and orientation of the object. It is not just the surface area or the forward area of the object as presented to the flow, it depends on the entire shape of the object.
Counterintuitively, the air/water resistance felt by a moving object can be shown to depend more on the shape of the back end rather than the forward end of the object. Typically, its better to have the back end long and tapered. This is what makes the typical design of cars so ridiculous: having the front (hood) curved and tapered does nothing for the overall air resistance if the back end is blocky and chopped off, as it usually is nowadays. The engineers that design cars are very aware of this, but they have been forced to build cars that match the general public's (incorrect) intuition about what reduces air resistance. Its kind of a running joke in the fluid dynamics community.
Examples of rare vehicles well-designed to reduce air resistance:
Old-style Airstream trailers: http://www.pamotor.com/cars/Airstream 1968 Trailer/Airstream LF34.jpg
Those solar-powered cars engineering students are always designing for contests and races:
 
Hmmm, cars like that might reduce rear-end collisions. (Get off the d*mn cell phone and pay attention to your driving!)
 
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