A Moment of Science

Flying in a Crutch

Who can walk faster, a ballet dancer whose leg muscles are extremely fit, or a couch potato whose legs are soft and flabby?

Did you ever have a broken leg?  Or did you ever see someone else in a cast? If so, you may have noticed something odd when the crutches come out.

You would think that person would be the slowest in the crowd, just hobbling along. But that is not so. Once someone becomes comfortable moving around on crutches, they can often move very quickly, even outpacing uninjured folks. What’s going on here?

The answer is found in the dynamics of walking. Ask yourself the following question: who can walk faster, a ballet dancer whose leg muscles are extremely fit, or a couch potato whose legs are soft and flabby? We’re not talking about running now, just about walking.

The answer? Whichever one is taller.

Yep. Leaving aside issues such as weak knees and just speaking in general, muscular ability does not determine walking speed. It’s the length of the leg that does it. Little children have to run to keep pace with a walking adult not because their muscles are weak but because their legs are short.

Now, let’s think about the person with the broken leg. True, one leg is out of commission and there’s the extra weight of the cast. But if you watch a person on crutches walk, you’ll notice that they keep both legs together with their torso and pivot from the shoulder.

The body swings forward as the crutches lean back, and vice versa. That way they can move as if the majority of their body were two gigantic legs. Their stride effectively becomes that of someone about twice their actual height.

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