Walking same distance different speed - energy consumed?

DapperKay

This is a question in general, but I am asking it after I observed MapMyFitness.

If you use their calculator - I do that sometimes to check how much calories I burned when I am away from home and do a lot of walking.

I noticed that when I put in the exact distance walked, the amount of calories burnt change as I increase the time. This is strange, surely you exert the same effort to walk that distance whether you do it in 30 minutes or 60. This isn't about respiratory health or endurance, just pure physics says that the energy needed to walk distance x would be the same regardless of velocity.

Am I wrong to assume this?

To illustrate the example - on MFP.

Walk 5km in 60 mins - burnt 2118 KJ
Walk 5km in 360 mins - burnt 3764 KJ

I'm confused...

weird_me2

In the example you have, you are going to want to account for your bmr for the 5 extra hours. I'm guessing that if you used a calculator to figure out your calories burned during rest. I've found mapmywalk and mapmyrun to be fairly accurate.

Abowles27

It's because you're looking at distance and not duration. I mean who would take basically 2 hours to walk a mile. But in that 2 hours, you could have walked over 6 miles and be at 4236 KJ. Also, it's higher because there is a point where it's so slow that even though you are burning less calories/minute the minutes outweigh the calories/ minute if that makes sense. So like if you burned 2 calories/ minute running 7 minutes for a mile which would be 14 compared to 1 calorie/minute but walking for 30 minutes for a mile. The latter is more because the minutes eventually outweigh the expenditure of energy.

Strokingdiction

It has to do with efficiency. The human body is very efficient at certain speeds. The most efficient speeds would be the lowest calorie burns. Start to walk faster and it becomes a much less efficient form of movement, hence the higher calories required to move at that velocity. In fact, you'll find that at a certain speed, it's actually easier for the human body to break into a jog than continuing at that high rate at a walk. So a fast walk of 4.5 mph will actually burn more calories than a jog at 4.5 mph.

DapperKay

It has to do with efficiency. The human body is very efficient at certain speeds. The most efficient speeds would be the lowest calorie burns. Start to walk faster and it becomes a much less efficient form of movement, hence the higher calories required to move at that velocity. In fact, you'll find that at a certain speed, it's actually easier for the human body to break into a jog than continuing at that high rate at a walk. So a fast walk of 4.5 mph will actually burn more calories than a jog at 4.5 mph.

Good answer - I still think that physically speaking, it takes the same amount of energy, regardless of efficiency. The concept of efficiency stipulates that you can do something burning less calories than you would have done if you were less efficient (relatively speaking). That I get, but surely once you are efficient then you will be efficient regardless of how long you spend on that distance. What I am saying is that if you are efficient, then it is an overall state that governs your every move, not a momentary concept that happens when you change pace and then you lose that efficiency if you go back to being slow.

If it will take you X calories to do event Y, then physics says it will take X calories regardless of the amount of time it takes. However, if what you are saying is true, then the rule holds, only that it will take X calories to do event Y within a certain bracket, and that bracket is governed by your efficiency at that bracket. I just struggle to see how you can be more efficient for 10 minutes and then lose that efficiency if you slow down your speed. Surely if fitness is a factor, then your overall fitness hardly changes over this short amount of time...