system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Does running vs walking an equal distance use the same amount of energy?
gpt
It depends what you mean by "energy".

Running and walking a mile are both going to move the same mass the same distance, so in terms of physics, you did the same amount of work and expended the same amount of energy.

In terms of calories, running is going to usually go burn a few more for a given distance.  Running uses energy a little less efficiently, especially if you run fast enough to get into the anaerobic range.  At that point, your body isn't getting enough oxygen, and has to rely on a much less efficient process to convert glucose into ATP.  

On the other hand, your body will burn a certain amount of calories each hour, 50-100, just being alive.  This is kind of a calorie tax on anything you do, so if you were very fit and walked very slowly, the tax you pay might be more than what you save in efficiency.

Finally, there is our perception of energy and fatigue.  Your cells burn glucose for energy, and glycogen is your bodies main short-term energy reserve, as it can be readily converted into glucose.  Usually, there is enough in the muscles to do whatever you need them to do.  When that is exhausted, there is glycogen in the bloodstream that can replenish it.  When that is exhaust, more is stored in the liver.  And when that is exhausted, your body has to start converting fat into glucose.  

Each of those steps represented an additional level of fatigue, as your body has to replenish the various reserves as they are exhausted.  That is why sprinting a mile will leave you feeling more tired than walking five miles, even though it used fewer calories.  Walking burns calories slowly enough glycogen can be replenished as you go, while running will result in a deficit.