Science Explains Why We Bend Our Arms While Running

Whenever we run, our legs do a lot of the work, taking continuous steps in front of the other to propel us forward and cover long distances. However, have you ever noticed how your arms would swing as well? And is there a scientific reason behind this?

Our arms certainly don’t swing as much whenever we walk. In fact, for most of the time, they just naturally hang straight at our sides. However, unless we try to (much like the ninjas from the animated show Naruto), our arms would naturally swing at our sides when we start running. So why is this so?

Arms Wide Open

As it turns out, our arm positions affect our overall energy efficiency. This means that walking with bent arms actually uses more energy than walking while they’re just hanging naturally at the side.

To understand this more, a team of researchers decided to use eight volunteers (four men and four women) and examined their movements while they’re on a treadmill. These subjects were then asked to both walk and run, careful to make sure that they do it with both bent arms and straight arms. The subject’s movements were then captured by infrared cameras and motion-capture software then converted into 3D digital models.

The exercises were repeated two weeks later to capture their metabolic data that would represent how much energy they’re using.

From the data, the researchers were able to find out that walking with bent arms requires more energy, with the volunteers’ energy expenditure increasing by about 11 percent. This shed light on why people walk with their arms at their sides. However, the study was not able to find out the reason why running always comes with bent arms.

With that however, a study back in 2014 stated that it’s because running while making the effort to keep your arms at your sides require more energy, and running with arms swinging reduce torso motion.

Per the researchers, this relationship between our gait and our arm movements could also help shed light on how our arms evolved along with our family trees.

"Modern arm proportions emerged in  Homo erectus , and coincided with the evolution of endurance running as  an important hominin behavior," the researchers added.

Running Exercise Researchers from Hong Kong developed a new wearable technology that collects energy as you walk and provides power to mobile devices. Pixabay