Why We Do? What We Do?

The ancient Greeks used to say, "Know Thyself". Our bodies are amazing machines and they do some amazing things and most often we do not even sit and think why do we do or move certain body parts in certain way. We just do it because it comes naturally. All the bones in our body form a magnificent framework that gives our body its structure; let us move in many ways. The ribs that are curiously bent, joining the chest bone and the backbone together to form a box called the rib cage, this is to protect some of the important internal parts of our body like the heart, the lungs and the liver that lie protected inside the rib cage. The spine and the backbone that helps us to bend, twist and hold our body upright. The bowl shaped structure of the pelvis that encloses the portion of our body below the stomach. The pelvis helps us to sit on, acts as a tough ring of protection around the parts of our digestive system, urinary system and our reproductive system.
Different human movement is achieved through a complex and highly coordinated mechanical interactions between the bones, bone joints along with the muscles and ligaments controlled by the nervous system. Over a period of time many doctors, researchers have tried to analyze and understand the biomechanics of the human body. Why we do what we do. That brings us to a very common phenomenon that we see and experience regularly but may have never given it a second thought. Why do we bend our arms when we run or try to walk really fast?
Though while walking or running it is our legs that do most of the work but our arms are involved too. Try walking faster or run and we will find our arms automatically bend which otherwise usually hang naturally at our sides and are mostly straight. However, as soon as we start running our hands bend at the elbow and swing as well. Researchers investigated this common phenomenon and found that though we bend our hands at the elbow while running it is actually less energy efficient than walking with arms hanging straight. Can we run with our hands hanging straight? Not really, it feels awkward.
During the research it was found that when the subjects were made to walk with bent arms their energy expenditure increased by 11% as it took an effort to keep the arms bent while walking at a slow pace, "but the reason for the stereotyped bent arm running still remains unclear". According to a study conducted in 2014 showed that arm swinging costs energy while running but holding them straight took even more effort and energy which was because, when the arm swings while running or walking briskly it reduces the motion of the torso.
The relationship between our arm movement and gait also could explain how the arm proportion evolved in the human family tree. Think about our extinct relatives Australopithecus and Homo habilis, who lived millions of years ago, had arms that were longer relative to their legs unlike modern humans. Probably shorter arms benefitted modern humans during long distance running.
By: Madhuchanda Saxena
Content: https://www.livescience.com/why-arms-bent-running.html