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Why Do We Bend Our Arms When We Run?


Whether you are a professional runner, or just taking a quick jog to the mailbox, you will run with a specific form. Most people have the same form that varies a bit depending on their gait. When you walk, you keep your arms down by your side, and they swing a bit. When you run, you bend your arms at the elbow. Have you ever wondered why do we bend our arms when we run? If you have, you’re not alone. Researchers have been investigating how yarm position affects energy efficiency. What they found is pretty shocking.


The researchers who were investigating how yarm position affects energy efficiency found that walking with bent arms is less energy efficient than walking with straight arms. They believe that a bent arm has a shorter arc than a straight arm. When the arms are bent, they require less energy to swing back and forth. According to the researchers, walking or running with your arms bent is more efficient.

Why Don’t We Bend Our Arms While We Walk?

If bent arms are more energy-efficient, why don’t we naturally bend our arms when we walk? To find out, a group of researchers worked with eight test subjects. Four of them were men, and four of them were women. They had the subjects both walk and run on a treadmill. They had them walk on the treadmill, and then run. The researchers used infrared cameras and motion-capture software to record the movement of the subjects. Next, they constructed 3D digital models of their bodies.

Two Weeks Later

Two weeks after the initial experiment, the test subjects were sent back to the treadmill. This time, they were wearing breathing masks. The masks allowed the researchers to collect metabolic data that could show how much energy the participants were using. When the subjects kept their arms straight, they all said that it felt awkward to keep their arms straight. The researchers found no significant difference in the energy efficiency. Whether their arms were bent or straight, there were no real changes.

Walking With Bent Arms

When the test subjects walked with their arms bent, their energy expenditure increased by 11 percent. The researchers believe that this is because it takes more effort to keep your arms bent while walking at a low speed. Although this research helped them understand a bit about why people naturally hold their arms straight when they walk, they still don’t know why the reason for stereotyped bent arms while running is still unclear. A 2014 study shed a bit more light on this.

The 2014 Study

A study on the subject was performed in 2014. The study found that swinging your arms while running uses additional energy; however, holding them steady takes even more energy. This is because when you swing your arms, it reduces the motion in your torso. The results of this study were later published in the Journal of Experimental Biology. The published study states that the relationship between the arm movements and a particular person’s gait can explain how arm proportions evolved in humans.

Our Ancestors

Our ancestors, Australopithecus and Homo habillis, lived millions of years ago. Their arms were longer relative to their legs than we have today. Their forearms were longer compared to their upper bodies. Because their forearms and arms overall were shorter, it meant that they would swing less. Arms like out ancestors would be beneficial to long-distance runners today. According to scientists, this trait could have shaped the evolution of the human arm bone’s length.

What Does This Mean?

This means that as the years went on, our arms grew to be longer than our ancestors. As time went on, we relied less on our legs to get around. Our ancestors had to run from predators, which meant that to survive, they had to run fast. Having short arms helped them accomplish this. Running was the only way to get away in most cases. As humans evolved, our arms got longer, because we didn’t have giant predators wandering around.

Running and Speed Walking

When you are speed walking or running, bending your arms not only feels comfortable, but it takes less energy to keep your arms bent. The researchers in the study believe that this is the reason that we bend our arms naturally when we run or walk fast.

Your Own Experiment

The next time you are jogging or even out walking, you can put the theory to the test. When walking fast, try to keep your arms straight. You will see that it takes more energy. This will be even more obvious when you try running with your arms straight. After doing your own experiment, you will be able to understand why you bend your arms while running.

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