Burning Calories vs Work Performed

The runner does more work than the walker, for one thing by bouncing harder on the ground.

Ok, I get that, but besides that factor would there be any difference in calorie burn?

I would say that the runner burns more calories because he gets hotter, which forces the body to produce more sweat, which would burn more calories than the person at a slow walk and sweating less.

Just like a car burns more fuel to go fast from point A to point B, rather than slow, so it goes with the human body.....................it's more work to go fast.

It may be more work to go fast, but then you do that work for a much shorter period. It could be 12 sec of sprinting and 40 sec of walking. So I agree the rate of calorie burn is higher but for a shorter period

Now you made me look.

Yes, in other words the sprinter generates more power (joule per second (J/s)), so it makes sense that s/he would sweat more, yes?

Might depend how much of the persons body bounces up and down (hey, I'm thing bear-belly, absolutely nothing else)

GA for that.

On level ground, force X distance = 0 except for wind resistance, which goes up as the square of speed. A bigger factor is that when walking, the legs move at their natural period as pendulums, but have to be forced for running. That is why runners lift their feet higher, and why animals have only tendons in their lower legs. There is also the higher rate of power being produced, which not only needs a higher rate of cooling, but uses less efficient anaerobic processes. The lactic acid produced causes sweating after the run.

BTW, You can carry 30% of your body weight on your head with no increase in energy use, due to the improved synchronicity of natural rhythms in the body parts.

Why do you say that the force x distance = 0? Your statement completely ignores the acceleration required to reach "cruising velocity".

A walker achieves maximum velocity with minimal force over a distance of less than 5 meters. Walking consists of leaning forward and allowing gravity to pull you down until you move a foot forward to keep from falling. The gravity assist reduces the amount of work required for walking. The primary energy expended in walking is due to repetitively cycling the legs forward to keep balance. A walker always has at least one foot in contact with the ground. A sprinter, on the other hand, has at most one foot on the ground and is airborne between steps. He must exert significant force against the ground and overcome gravity to break contact with each stride.

Usain Bolt, current world record holder in the 100m dash, accelerated for over 6 seconds at an average rate of 3.07 m/s² before reaching his top speed of 12.4 m/s at a distance of 60+ meters after leaving the starting line. The force required to produce that acceleration is amazing. The fact that he can keep it up for so long is simply phenomenal. He's the only one in the world who can do it.

In a parallel universe, perhaps. As others have already pointed out, kinetic energy is related to mass and square of velocity. The body is perhaps 30% efficient in converting chemical into kinetic energy, and the heat production is considerably more when running, hence the sweating.
Walking is not initiated by leaning forwards. It involves active extension of one hip and active flexion of the other hip, with corresponding active movements of the knee and foot, and can be performed with the trunk extended backwards. You are, however, correct in noting different actions in walking and running, though this ignores the action of race walking, in which one foot is always on the ground, yet forward progress is quite fast.
I do not know of any animals that "have only tendons in their lower legs".
Power is rate of work. By "higher rate of power being produced" I presume you mean "higher power being produced".
Lactic acid does not produce sweating. Sweating is the body's response to a raised temperature. If the body's pH drops (which is the effect of the lactic acid), the response is increased ventilation.
As for "BTW, You can carry 30% of your body weight on your head with no increase in energy use, due to the improved synchronicity of natural rhythms in the body parts" I would very much like to know where you get that idea from, because I have no idea what "improved synchronicity of natural rhythms in the body parts" means.

GA...walking is a controlled 'fall'. We fall forward and then swing a leg into place just in time to prevent the full face-plant. I believe most of the energy used in walking is in smaller muscles involved in maintaining balance. I think the error is in trying to view the mechanics of walking as analogous to a machine moving from point A to point B. The body consists of dozens of small machines. Many of these 'machines' that are hard at work during running are just idling when we walk.

Well put.

On level ground, ignoring internal muscle friction, air resistance, etc moving 100 yards accomplishes no work (in the basic physics sense).

You've given a good summary, I think, of some of the many factors that change the calorie input vs the real work (which goes into flexing shoe soles vs hysteresis, flexing the ground underfoot, joint friction, internal muscle friction, wind resistance, etc.)

Re 30%... do you have a link to offer support? This is the sort of thing that makes cr4 addictive... and such a time sink. Suppose you provide a link to a couple articles... then I read those... and there are additional links within the articles... and night falls, and I wonder where the day went.

On level ground, ignoring internal muscle friction, air resistance, etc moving 100 yards accomplishes no work (in the basic physics sense).

I always thought it was returning to the start that cancelled out any work done: work = mass * displacement.

The displacement must be in the direction aligned with the force. So in a physics text (in which they say things like "ignoring friction") when you move a box along a level surface, you accomplish no work. If you lift the box, you accomplish work.

When you add in air resistance, frictions(s), etc. then work is done.

If, in a frictionless world, you move a box 100 feet horizontally, you do no work.

Yes. However, the increased rate of energy expenditure makes the heart labor more and the body sweats. The extra factors mentioned by the other posters play an additional part.

Depends on how much beer he drinks after he stops walking.

DOES he really sweat more for the "same work done"? Or does the sweat excreted just have more time to evaporate when one walks, therefore making it only appear that the runner has sweat more? (I don't know, but enjoyed reading the discussion)

Anaerobic vs. aerobic. Your aerobic energy system does most of the work most of the time, whatever you're doing. When you need the power quickly is when you produce power anerobically. This produces a lot more power, but is also short-lived and produces "waste" (lactate and heat).

(It's been a while since I studied this, so I might get something wrong. I'm sure someone will correct me.)

The ATP-CP anaerobic system uses ATP molecules stored in muscular tissue to provide instant-on power. It lasts a few seconds depending (I think) on your muscle mass. That's what we use when dodging a speeding car or rabid dog. Your aerobic metabolic process starts reloading those molecules immediately - and that burns calories. If you completely deplete your muscles (to whatever extent they can be depleted), then you might burn extra calories for an extended period of time. It's called EPOC, excess post-exercise oxygen consumption.

I don't know the most common name for it, but the other anaerobic pathway is what we think of most when sprinting. Blood sugar fuels an anaerobic process that produces power not quite as well as the ATP-CP system, but a lot better than the aerobic system. At full bore, it burns out in roughly 30 seconds. (I don't care who you are.) You can stay anaerobic for a longer period of time by carefully dosing your sprint, but you're going to need to throttle back and breathe in a couple-few minutes. This process also produces lactate and much more heat, and your body attempts to regain homeostasis (pH and temperature balance) immediately. If you drain your body of blood sugar to the point of collapse, it can take well over 24 hours to replenish it.

Endurance athletes sometimes use all three energy pathways 100% (functionally speaking) for extended periods of time. Usain Bolt doesn't have time to get much out of his aerobic system, but it's what keeps him going when he's not racing.

Newton's first law F=Ma. Here, a is the answer to your question. More force is applied when running because you give your mass a bigger accel than when you walk.

Bigger force, same distance, more work done, more heat generated, more sweat! Other answers in this thread are more complete than mine, but this basic law applies, even if the force is in fact an impulsion.

Human body is a thermo-dynamic engine. It releases both sensible and latent heat under various activities. When he walks at slower speed these values are different than he runs and he sweats more.

Just to round-up a few misconseptions.

a: Body kinetic energy is something that appears just twice in the body travel. When accelerating and when decelerating it. So for the the actual 'travel' is irelevant. Energy for 'travel' is consumed elsewhere.

b:Power required to move the body doesn't have to do with speed only. Ther's a speed range (specific for every individual) that running (which is faster) consumes less calories per distance than walking. You can ask a long distance walker about it. Running on a walk race is cheating.

c:Work of a force is the product of the force's applied point travel with only the force's component parallel to that travel.

d:In all cases sweating means that the heat-control mechanism is energized because body needs to expell more calories per time, not per meter. S.M.

Why has no-one mentioned momentum, surely more speed = more momentum and more momentum = less force/effort to keep the body moving foward. In this case the runner has more speed and therefore more momentum and therefore he covers a meter easier than the walker? - (just from a layman's point of view)

I still have not received a conclusive answer to my original question

I don't think the extra momentum gives any "freebies"; after all, where did it come from but the runner's extra effort to get up to speed?

Why has no-one mentioned momentum, surely more speed = more momentum and more momentum = less force/effort to keep the body moving foward.

In the basic physics sense, momentum has no effect on the force required to keep a body moving at a constant speed. An orbiting space craft moves by momentum alone - no force is required. Force is required only to accelerate (change the speed) of the body. In running (which is a very complex biochemical-mechanical process) many other things come into play: slow twitch vs fast twitch muscles, speed and direction changes in the limbs, the ratio between foot distances moved vs distance across the ground, etc

I still have not received a conclusive answer to my original question.

The runner burns more calories. There are some speeds at which walking (a fast walk) and running (a slow run) use the same calories per mile. But otherwise, going slower burns fewer calories per mile (even though that mile takes longer to travel).

Here's an article with some data. Calorie burn rates are shown only up to 10 mph (amateur marathon runner speed). (A fast 1/4 miler can run at about 20 mph, and a super fast sprinter can run at 23 mph.) You can see the trend, and I'd guess that a fast sprint runner is burning 200 calories per mile: the stride is less efficient (arms and legs move more per foot across the ground), wind resistance is coming into play, etc.

let's make it fair, and have the walker facing a wind of (say) 20mph. OK, bit silly, but it seems to be a number of factors such as gait and the other stuff mentioned.