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Why don't People Fall, when their Arms Swing?
June 30, 2010 22:49

When a standing person moves, any kind of motion changes body configuration, and centre of body’s mass shifts. In order to prevent a moving person from falling, a huge coordinated work of muscles, responsible for motion, and postural muscles, helping keep upright body position, is carried out. Russian scientists from the Institute of Information Processing (Russian Academy of Sciences) decided to find out how mentioned coordination was conducted. Scientists came to a conclusion that both groups of muscles were responsible for keeping position the same while moving.

Researchers conducted a series of experiments, in which standing upright required various efforts. The experiments were carried out on volunteers – six healthy males of various ages took part in the research. Initial position was the following: hands of a volunteer were hanging down along the body. Then after a green light switched on and a sound beeped, a volunteer was asked to raise his right hand and to point at a target as quickly and accurately as he could. Several seconds before the signal, scientists told volunteers to get ready. Men, who participated in the experiments, raised their hands while standing or sitting on a chair. In an upright position volunteers were tied to a stable object with rigid straps either near pelvis, chest, or near both body parts. Sitting experiment also had three variants - a volunteer could put his feet on the ground; his feet were hanging loosely; and he could put his feet on the ground, and his chest was fixed. Scientists recorded activity of various groups of muscles, and acceleration, with which volunteer's hand moved.



Walking and swinging hands
The more stable a posture is, the less effort you need to keep it. That is why postural muscles change their activity depending on a volunteer’s posture, and activity of muscles, lifting his hand, remain the same. When a volunteer hears the word “Ready”, some of his postural muscles become active in advance. In other words, posture control system plans ahead what to do to prevent falling, when a man raises his hand. When a posture is stable, very few or even no muscles are active. However, majority of postural muscles, including thigh muscles, get ready to move even when their owner is sitting, moreover, their activity is the same as that of muscles, responsible for raising a hand.

Scientists suggested a hypothesis that a posture is kept unchanged with help of both systems: postural control system and motion control system. Postural control system works in advance, before a volunteer moves. As for the second system, motion control system “knows” about initial posture and plans work of muscles, responsible for motion, as well as of some postural ones. This means that motion control system looks after hand motion and at the same time prevents the one, who moves, from falling.

Authors of the research think that these two processes are independent and take place simultaneously.

Source: Science News

Kizilova Anna

Tags: Russian scientists Russian science health   

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