# Would increasing something in size change the speed of its movements ? Example: if a human doubled its size, would it run faster, slower, or the same speed?

Depends on mass, not size. Say a giant weighs 50 kg and a midget also weighs 50 kg. The size wouldn't matter. Other factors would come into play. But practically speaking, a double in size would definitely increase the mass so the answer to your question is indirectly yes. (But it is not a proportional increase.)
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I'm just going to give you something to think about---

Let's say two men are going to walk for 3 hours.  The inseam measurement for one is 30 inches and the second man has a 34 inch inseam.

If each has a "normal" stride motion, how much ground will each one cover.

(Think isosoles triangles.)

(Also, remember, you can only multiple size so much before the resulting animal's structure can support itself.)

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Anything that gets bigger such as a Human gaining weight and goes out to try running , i would think they would run a lot slower than usual really hard to say. Course there was some Man who weighed close to 300 lbs and he was one of the worlds fastest overweight runner and even doctors prove that he was as healthy as can be.