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  #1361  
Old 11.01.2013, 11:35
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Re: Ask a Scientist

I did that, immediately after you posted, but you rudely dismissed my answer. I thought you were meant to be nice.
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  #1362  
Old 11.01.2013, 11:51
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Re: Ask a Scientist

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OK....one for the scientists....

So I'm a trained engineer and physicist so I know about mechanics and energy and power and stuff....but

If I run 10 km, then I will use an amount of energy required to haul by 84kg ass around a 10km route.....in my physics mind, that amount of energy shouldn't change on speed. If I do it faster, I need more power, but I need it for a shorter period. If I go slow, less power but for a longer period. Same energy used

So how come if I run the route fast, I apparently burn more calories than if I do it slow? Its instinctively true of course, but what is the science?

Thanks
- efficiency, is your body uniformly efficient at all speeds? you are assuming it is.
- wind resistance. is not linear with speed (you said you studied physics??)
- rest energy. if you sat there like a potato for an hour, you'd still burn energy in spite of note moving. this needs to be incorporated
- etc. etc. etc.
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  #1363  
Old 11.01.2013, 12:06
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Re: Ask a Scientist

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- efficiency, is your body uniformly efficient at all speeds? you are assuming it is.
- wind resistance. is not linear with speed (you said you studied physics??)
- rest energy. if you sat there like a potato for an hour, you'd still burn energy in spite of note moving. this needs to be incorporated
- etc. etc. etc.
I'm assuming I don't know

I don't think that wind resistance is a factor - at least not that significant at the difference between a 5:30 min/km and a 5:00 min/km

Anyway, I think I found the answer.....the physics I remembered were the equations for potential energy, whereas kinetic energy ie the energy required for movement is a whole other set of calcs (all came back to me)

(So the energy = 1/2 mass * velocity squared - so it IS dependent on the speed at which you run)
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  #1364  
Old 11.01.2013, 13:25
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Re: Ask a Scientist

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I'm assuming I don't know

I don't think that wind resistance is a factor - at least not that significant at the difference between a 5:30 min/km and a 5:00 min/km

Anyway, I think I found the answer.....the physics I remembered were the equations for potential energy, whereas kinetic energy ie the energy required for movement is a whole other set of calcs (all came back to me)

(So the energy = 1/2 mass * velocity squared - so it IS dependent on the speed at which you run)
Yes, but the total energy expended is going to be the integrated energy vs. time curve, which will be shorter for the 5 min/km run.

The proper thermodynamic analysis will define the system as the runner's body, using the equation

Change in energy = Energy in - Energy out + Energy generated

Energy comes in a few different forms in this problem on both the input and output side: heat, work, and enthalpy (energy carried in and out with material crossing the system boundary, such as air inhaled, air exhaled, and sweat) I don't really want to go into a detailed analysis of this problem, but we know that when you run faster, your body is less efficient, so you lose more energy as useless heat. This is shown by your body sweating more, so your sweat can carry off some of this useless heat (which would be considered in the enthalpy part).

You are confusing a state function, energy, with path dependent functions, such as heat and work. If your stride doesn't change significantly from 5.5 min/km vs. 5 min/km, then the amount of work doesn't change. The amount of heat, however, certainly does.

To sum up, pretty much everyone who answered your question is correct.
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  #1365  
Old 12.01.2013, 16:08
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Re: Ask a Scientist

Isn't car also burning more gas when running fast pace?

I think metabolism isn't so regular, though, the min your body gets used to routine, your fast pace burning will change and you will have to alternate, circuit or run faster in order to burn as much.
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  #1366  
Old 12.01.2013, 22:39
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Re: Ask a Scientist

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Isn't car also burning more gas when running fast pace?

I think metabolism isn't so regular, though, the min your body gets used to routine, your fast pace burning will change and you will have to alternate, circuit or run faster in order to burn as much.
re. cars Yes it does, but that's because of drag, which increases faster than speed at high speeds. So that factor is not relevant for running.

Although part of the improvement in performance caused by training is due to higher efficiency, mainly it is due to gaining a capacity to use more energy (more enzymes in the muscles, better oxygen throughput...). So top athletes can burn more energy than the untrained.
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  #1367  
Old 22.01.2013, 07:03
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Re: Ask a Scientist

Here are my questions.

When viewed through a telescope far worlds are seen as they were 1,10,100,1000 light years ago. Assuming that a telescope is so powerful that a family can be seen having a picnic on one of those far star's planets (all those light years ago), how is it if I could travel at such an extraordinary speed that I could catch up and pass light before the light from the time of my birth on this planet reaches me - would I then, when the light catches me up, then be able, at the due time, to see myself being born?

Does light travel in one direction or go everywhere at the same speed?

If light shows us what happened in the past, as above, could we see the Big Bang?

And finally; assuming that all this is possible then it would appear that everything that's happened everywhere in the universe, is, under the assumption that the speed of light could be overtaken, still visible to an observer - so when does it stop being visible to an observer who fulfills the requirements?
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  #1368  
Old 22.01.2013, 10:34
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Re: Ask a Scientist

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Here are my questions.

When viewed through a telescope far worlds are seen as they were 1,10,100,1000 light years ago. Assuming that a telescope is so powerful that a family can be seen having a picnic on one of those far star's planets (all those light years ago), how is it if I could travel at such an extraordinary speed that I could catch up and pass light before the light from the time of my birth on this planet reaches me - would I then, when the light catches me up, then be able, at the due time, to see myself being born?

Does light travel in one direction or go everywhere at the same speed?

If light shows us what happened in the past, as above, could we see the Big Bang?

And finally; assuming that all this is possible then it would appear that everything that's happened everywhere in the universe, is, under the assumption that the speed of light could be overtaken, still visible to an observer - so when does it stop being visible to an observer who fulfills the requirements?
A lot of questions. I'm not a scientist but read up on this stuff (to the limit of my ability to understand!) a while ago.

Your first issue of seeing yourself born is "solved" by hard limits to the speed you can travel at. You can't travel faster than the speed of light. If you did, you would be going "back in time" (at your point of observation) and hence yes, would see yourself being born.

This isn't too different to severely "slowing down the speed of light" by, for example, videoing your birth and watching the replay You're not existing before you were born, just watching it.

Could you see the big bang? Well, by observing stars we're looking at them at the point in time when the light (that we use to see them) left the star. So in order to see the big bang we'd need to see a light generating object that existed right at that point. So we can only see as far back as to when light existed. Of course, we can build detectors that register other particles, so a detector could "see" further back than we can with our eyes, but again we need to actually detect one of those particles. Now, these particles travel at the speed of light so if they were emitted at the big bang point itself, they are now at the far edge of the universe and we've already missed our opportunity to detect them. So we could only measure them from left over interactions that are in their path of travel.

Light is carried by photons (a dual wave/particle entity) and has direction. Photons are generated when energy is released from an atom when its energy state changes (an electron moves orbit after having previous been "excited" into a higher energy state). More photons, more ligth spread. Plus the speed of light is as it is when travelling in a vacuum (a vacuum being what we consider to be empty space, which is probably totally full of things we don't understand such as the Higgs field and dark energy/matter) and is slowed down when going through objects (objects which don't actually block or reflect the photon) such as glass.

If you could travel faster than the speed of light and can overtake it (and hence get outside the boundary of the universe to see the big bang remnants) then yes, you could travel around seeing everything which happened. But as faster than light travel isn't possible*, the question doesn't come up. *Maybe it is, but only for particles which have no mass. So you'd need to go on a diet.
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  #1369  
Old 22.01.2013, 11:12
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Re: Ask a Scientist

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Here are my questions.

When viewed through a telescope far worlds are seen as they were 1,10,100,1000 light years ago. Assuming that a telescope is so powerful that a family can be seen having a picnic on one of those far star's planets (all those light years ago), how is it if I could travel at such an extraordinary speed that I could catch up and pass light before the light from the time of my birth on this planet reaches me - would I then, when the light catches me up, then be able, at the due time, to see myself being born?

Does light travel in one direction or go everywhere at the same speed?

If light shows us what happened in the past, as above, could we see the Big Bang?

And finally; assuming that all this is possible then it would appear that everything that's happened everywhere in the universe, is, under the assumption that the speed of light could be overtaken, still visible to an observer - so when does it stop being visible to an observer who fulfills the requirements?
Time Dilation

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In theory, and to make a clearer example, time dilation could affect planned meetings for astronauts with advanced technologies and greater travel speeds. The astronauts would have to set their clocks to count exactly 80 years, whereas mission control—back on Earth—might need to count 81 years. The astronauts would return to Earth, after their mission, having aged one year less than the people staying on Earth. What is more, the local experience of time passing never actually changes for anyone. In other words, the astronauts on the ship as well as the mission control crew on Earth each feel normal, despite the effects of time dilation (ie. to the traveling party, those stationary are living "faster"; whilst to those stood still, their counterparts in motion live "slower" at any given moment).
Yes, it gets complicated.... and no I don't really understand it.
I just remember this from Physics at school (which was a long time ago)

But yes, adrianlondon is quite correct, time is linked to the speed of light.
An Astronaut who go into space with synchronised watches will have a slightly faster time with mission control when they land.
(It's bugger all, but it has been measured).

The faster you travel the slower time becomes. Faster than the speed of light and time would move backwards.....

If you observed a telescope on another planet and it was observing you, and let's say that you could speed faster than the speed of light towards the other telescope and look through it....... you would see yourself approaching the telescope you are looking through.
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  #1370  
Old 22.01.2013, 11:26
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Re: Ask a Scientist

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OK....one for the scientists....

So I'm a trained engineer and physicist so I know about mechanics and energy and power and stuff....but

If I run 10 km, then I will use an amount of energy required to haul by 84kg ass around a 10km route.....in my physics mind, that amount of energy shouldn't change on speed. If I do it faster, I need more power, but I need it for a shorter period. If I go slow, less power but for a longer period. Same energy used

So how come if I run the route fast, I apparently burn more calories than if I do it slow? Its instinctively true of course, but what is the science?

Thanks
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Body takes energy from different sources depending on how quickly it needs it. Plus the higher end heart rate requires longer for the metabolism to return to normal after the run. Plus a bit more resistance (muscles, air).

This is more of a medical question and I, also, would be very keen to hear a proper answer!
Again, I'm with adrianlondon on this.

The reason you use more energy is more 'Biological' than a static calculation.

Not going into detail here, but if you walk your body will use more fat reserves that it can access slowly and sustainably.

If you run fast, then the demand for energy increases and the body needs a faster source of energy to compensate for the defecit (blood sugar).

The used blood sugar basically becomes lactic acid and this is why your muscles hurt if you don't stretch after exercise.


This is also why people support the myth that walking burns more fat than running..... it's BS, it's only proportionally more fat but not less.

eg. (using basic numbers to illustrate)
If you walk you will burn 7 units of fat and 3 units of blood sugar. ( 7:3 ratio (10))
If you run and use twice the amount of energy, you will burn 8 units of fat and 12 units of Blood sugar. (4:6 ratio (double 10 =20)).
You still burn more fat if you run.

So the rate at which the body can utilise body fat is limited, and blood sugar access can be trained over time.
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  #1371  
Old 22.01.2013, 12:20
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Re: Ask a Scientist

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If you run and use twice the amount of energy, you will burn 8 units of fat and 12 units of Blood sugar. (4:6 ratio (double 10 =20)).
I think this is mixing up two topics i) the relative energy it takes to run vs walk due to bio-mechanical and other external factors, ii) biochemically where the energy comes from.

The ideas that moderate aerobic level of exercise burns more fat is pretty widely challenged nowadays. At the end of the day, fat is the human "battery" for a very large portion of energy reserves (a few seconds in the muscles, maybe a hour or so in the blood sugars, and days worth in the fat). There's also a view nowadays that high intensity training (intervals, heavy weights) ends up using more energy in total due to post training increased in metabolism and more muscle building. As long as you dont add more energy via food, the delta will come from your fat.

If you train in a fasted state your body learns to draw on fat pretty rapidly, but that doesn't mean that you will have lost more fat mass in total a day or two later than if you had your meal before the run all other things being equal.

But I very much doubt that the relative efficiency of these metabolic pathways are the main reason for the increased energy usage in running. Much more to do with the bio-mechanical efficiency of the gait and the wind resistance etc.
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  #1372  
Old 22.01.2013, 14:28
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Re: Ask a Scientist

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A lot of questions. I'm not a scientist but read up on this stuff (to the limit of my ability to understand!) a while ago.

Your first issue of seeing yourself born is "solved" by hard limits to the speed you can travel at. You can't travel faster than the speed of light. If you did, you would be going "back in time" (at your point of observation) and hence yes, would see yourself being born.

This isn't too different to severely "slowing down the speed of light" by, for example, videoing your birth and watching the replay You're not existing before you were born, just watching it.

Could you see the big bang? Well, by observing stars we're looking at them at the point in time when the light (that we use to see them) left the star. So in order to see the big bang we'd need to see a light generating object that existed right at that point. So we can only see as far back as to when light existed. Of course, we can build detectors that register other particles, so a detector could "see" further back than we can with our eyes, but again we need to actually detect one of those particles. Now, these particles travel at the speed of light so if they were emitted at the big bang point itself, they are now at the far edge of the universe and we've already missed our opportunity to detect them. So we could only measure them from left over interactions that are in their path of travel.

Light is carried by photons (a dual wave/particle entity) and has direction. Photons are generated when energy is released from an atom when its energy state changes (an electron moves orbit after having previous been "excited" into a higher energy state). More photons, more ligth spread. Plus the speed of light is as it is when travelling in a vacuum (a vacuum being what we consider to be empty space, which is probably totally full of things we don't understand such as the Higgs field and dark energy/matter) and is slowed down when going through objects (objects which don't actually block or reflect the photon) such as glass.

If you could travel faster than the speed of light and can overtake it (and hence get outside the boundary of the universe to see the big bang remnants) then yes, you could travel around seeing everything which happened. But as faster than light travel isn't possible*, the question doesn't come up. *Maybe it is, but only for particles which have no mass. So you'd need to go on a diet.
Ok, thanks adrianlondon.

Nevertheless, even if the speed of light cannot be broken, which I hadn't assumed - my questions were purely out of my imagination - but isn't it fantastic to think that the picture of (in this case my own birth) is still travelling through space and can still be viewed by some possible entity?
Or is there a stumbling block here?
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  #1373  
Old 22.01.2013, 14:32
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Re: Ask a Scientist

Nope! No stumbling block. As long as you were born outdoors and that the light emitting from that event passes by a planet containing life smart enough to have super duper detectors (which might not be an issue, as they don't need to be an advanced species now, only when the light from Earth reaches them).

One option could be in thousands of years (assuming we as a species haven't wiped outselves out by then) we may know how to break ourselves down into subatomic particles and use wormholes created to jump through extra dimensios, to get to a part of the universe faster than the speed of light (travelling not through extra dimensions). Then they could see your birth. Or they could just watch a youtube video.
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  #1374  
Old 22.01.2013, 14:58
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Re: Ask a Scientist

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Nope! No stumbling block. As long as you were born outdoors and that the light emitting from that event passes by a planet containing life smart enough to have super duper detectors (which might not be an issue, as they don't need to be an advanced species now, only when the light from Earth reaches them).

One option could be in thousands of years (assuming we as a species haven't wiped outselves out by then) we may know how to break ourselves down into subatomic particles and use wormholes created to jump through extra dimensios, to get to a part of the universe faster than the speed of light (travelling not through extra dimensions). Then they could see your birth. Or they could just watch a youtube video.
Well after they figure out how Quantum entanglement works then faster than speed of light communication may become possible & after that .....
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  #1375  
Old 22.01.2013, 14:59
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Re: Ask a Scientist

That would work on the principle of cloning, I believe. i.e. an entangled (and then split) copy of us would be created at some distant location.

Then what - bullet to the head of the original?
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  #1376  
Old 22.01.2013, 15:03
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Re: Ask a Scientist

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I think this is mixing up two topics i) the relative energy it takes to run vs walk due to bio-mechanical and other external factors, ii) biochemically where the energy comes from.

The ideas that moderate aerobic level of exercise burns more fat is pretty widely challenged nowadays. At the end of the day, fat is the human "battery" for a very large portion of energy reserves (a few seconds in the muscles, maybe a hour or so in the blood sugars, and days worth in the fat). There's also a view nowadays that high intensity training (intervals, heavy weights) ends up using more energy in total due to post training increased in metabolism and more muscle building. As long as you dont add more energy via food, the delta will come from your fat.

If you train in a fasted state your body learns to draw on fat pretty rapidly, but that doesn't mean that you will have lost more fat mass in total a day or two later than if you had your meal before the run all other things being equal.

But I very much doubt that the relative efficiency of these metabolic pathways are the main reason for the increased energy usage in running. Much more to do with the bio-mechanical efficiency of the gait and the wind resistance etc.
I don't think I've got it confused. I may have drifted unnecessarily into the 'fat' thing, and for that I appologise.

Back on topic, the original question basically suggest that:
"If an 84kg man walks 10km, he assumes he will use the same amount of energy if he runs the same distance."
The rationale being that the amount of energy used to run is elevated but by shortening time period used the result is the same.

Basically (using the number thing again)
If he uses 20 units of energy to walk 10km in 2 hours, (being 10 untis of energy per hour), he knows he will burn more energy if he runs 10km, say 20 units per hour.
The resulting amount of energy he theorises is the same.
i.e. 10 X 2(hrs) = 20, or 20 X 1(hrs) = 20.

The effect of wind resistance from 5km to 10km per hour will be negligible.
Sprinters in the 1990's liked those fancy full body space suits at the Olympics, but it doesn't seem to bother Usain Bolt too much these days.

What I'm trying to say is that if you walk 10km you will use less total energy than if you run the same distance in half the time because the amount of energy you require to accelerate and maintain your speed will disproportionately increase.

For example, (again not perfect)
A car will still travel a further distance if the engine is at an idle speed because the total amount of fuel used per 100L is less.
If you push it full throttle the average rate of fuel per 100km increases, so the efficiency of the fuel usage decreases.

Yes I agree that people range in metabolic rates whether they be mesomorphic to endomorphic, but the body still need to harness extra energy from somewhere else rather than fat reserves that 'trickle' like your battery example. The 'battery' output is capped and additional energy is required. Hence the increase in body temperature and breathing rate to process the amount of oxygen.


There would be absolutely no point in humans walking anywhere if we could run to the same location using the same amount of energy.
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  #1377  
Old 22.01.2013, 15:08
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Re: Ask a Scientist

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Again, I'm with adrianlondon on this.

The reason you use more energy is more 'Biological' than a static calculation.

Not going into detail here, but if you walk your body will use more fat reserves that it can access slowly and sustainably.

If you run fast, then the demand for energy increases and the body needs a faster source of energy to compensate for the defecit (blood sugar).

The used blood sugar basically becomes lactic acid and this is why your muscles hurt if you don't stretch after exercise.


This is also why people support the myth that walking burns more fat than running..... it's BS, it's only proportionally more fat but not less.

eg. (using basic numbers to illustrate)
If you walk you will burn 7 units of fat and 3 units of blood sugar. ( 7:3 ratio (10))
If you run and use twice the amount of energy, you will burn 8 units of fat and 12 units of Blood sugar. (4:6 ratio (double 10 =20)).
You still burn more fat if you run.

So the rate at which the body can utilise body fat is limited, and blood sugar access can be trained over time.
I still don't agree with either of you. My question isn't about where the energy comes from...my Garmin watch doesn't know or care about that. Its was about why more calories are needed to haul my ass faster when it is the same mass the same distance.

Like danny says...

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I think this is mixing up two topics i) the relative energy it takes to run vs walk due to bio-mechanical and other external factors, ii) biochemically where the energy comes from.
Anyway, I'm happy with my answer that its to do with the definition of kinetic vs potential energy that i wrote above
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Old 22.01.2013, 15:14
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I still don't agree with either of you. My question isn't about where the energy comes from...my Garmin watch doesn't know or care about that. Its was about why more calories are needed to haul my ass faster when it is the same mass the same distance.

Like danny says...



Anyway, I'm happy with my answer that its to do with the definition of kinetic vs potential energy that i wrote above
I'd guess running develops a lot more heat energy, both from chemical reactions and friction. That has to come from somewhere. But I'm only a code monkey, so don't rely on me.
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Old 22.01.2013, 15:30
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I'd guess running develops a lot more heat energy, both from chemical reactions and friction. That has to come from somewhere. But I'm only a code monkey, so don't rely on me.
correct, high intensity exercise requires a higher delivery rate of glycogen, in turn producing higher lactate build up, which also requires a catalyst, oxidization, to dispose of it so exercise may continue. Hence the body uses more energy than at a lower intensity of exercise, walking...something like that anyway.
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Old 22.01.2013, 15:34
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Re: Ask a Scientist

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I still don't agree with either of you. My question isn't about where the energy comes from...my Garmin watch doesn't know or care about that. Its was about why more calories are needed to haul my ass faster when it is the same mass the same distance.
Because maybe you should weigh 75kg instead of 84?


The faster you haul your arse, the amount of energy you require to accelerate and maintain that speed disproportionately increases.

Read the car fuel example above.(idle Vs full throttle)
Walking is a more efficient use of energy than running.


The Fat/Blood Sugar thing was just trying to explain where the energy comes from.
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