Does someone with short legs expend more energy walking the same long distance than someone with long legs? Of course when they step quickly.

Answer

Dear Mark,

The Dodentocht of Bornem (100 km walk) has just ended so I think this is a relevant question for more than ten thousand people!

Many people assume that long legs are an advantage because they take fewer steps, which seems more efficient (in other words, less energy is needed to cover the same distance). This implicitly assumes that each step “costs” the same amount, whether it is large or small, but that is unlikely (just try it). For example, people with long legs are usually taller and therefore heavier, and it is well known that moving a larger mass requires more energy. Where you then have the choice to express energy absolutely (how many Joules does a long-legged and heavier person A use to cover one meter compared to a short-legged and lighter person B), or relative, where you look at how much it costs to kg body weight. Depending on what you want to know, you can choose one or the other way of calculating.

As you can see, there are a few things involved, and common sense is not enough to provide an answer. In the scientific literature you will also find researchers who state that long legs are “cheaper” (because of taking fewer steps), but also researchers who find short legs advantageous. Short legs are much easier to swing forward than long ones.

In such cases it is nice that there are experiments. You just let people walk and look at connections between leg length and energy consumption. The latter is usually measured on the basis of the amount of oxygen consumed per meter travelled. What do these experiments teach us?

Taller people (who are therefore heavier but also have longer legs) consume more energy per meter walked than short people in absolute terms. However, in relative terms, ie per kg of body mass, they consume less (this generally applies to animals, by the way).

People whose legs are relatively long (i.e. longer than others of the same mass and height) walk cheaper. That also applies to walking.

The conclusion is therefore: to walk with little energy, you are quite small and light, but with relatively long legs.
Do you have long legs, but just because you are just tall in stature, you may or may not have an advantage depending on how you look at it (absolute or relative).
A simple example: if you have two people, one short and one 20% taller (but both of similar physique), the tall one will need more sandwiches to cover the same distance, but not 20% more sandwiches, rather 10% .
Or to put it another way: a truck consumes more than a Smartje, but consumes less per kilogram transported.

This applies to walking and running and may also explain why marathon runners (for whom the absolute energy they can absorb is limited) are rather small.

In your question you state that both people have to walk at the same speed. That is a minor problem, because the amount of energy you need to cover a certain distance is optimal at a certain speed when walking (this is much less clearly the case when walking). If you step slower or faster than that optimum, you will use more energy per distance traveled (so the feeling that strolling is more tiring than walking is not surprising). Now that speed depends on body size (and leg length), and is therefore higher for tall people.
If you let a tall guy walk together with a short guy who walks at his ideal speed, the tall guy will be disappointed (and vice versa).

I hope this is a bit clear! A short answer could have been “no, less” but I thought that was a bit simplistic, because there are too many “buts” and “ifs” in such an answer.

Kris