Comparative study of our movement: difference between astronauts and us




Comparing us on the ground with astronauts in space will definitely helps us to know what we actually do on the ground and what we had better do here on the earth. We will know characteristics of our environment more and well if we know different environment. Major difference between us on the ground and astronauts in space is to receive reaction force continuously and to receive friction (frictional force) by receiving reaction force at contact surface. We on the ground are really in advantageous condition to stop our body than astronauts.

However, we usually cannot think of ground reaction force and friction, and we forget that we have these forces to stop our body. This is because these forces are always there and there is no change on the ground. If there is no change, we usually won’t perceive it. When there is a change, we will perceive it like “there is something wrong”. Since most of us have never been to space, we don’t experience any change. We thus tend to ignore the fact that these forces are there, even though we are always receiving these.

An astronaut who plays the piano well cannot play the piano well in space like he/she does well when in the ground. Why? They can’t stop their body (some parts of their body) steadily in space. When the astronaut in space moves his/her arm to hit some keys with a certain speed, his/her whole body will be moved by this own arm action (by the joint reaction force of the arm movement). This happens because there is no continuous ground reaction force and thus unable to utilize friction force to stabilize the body. Since the astronaut cannot stop the body steadily, it is no wonder that the astronaut cannot play well.

This implies that our stabilizing activity (stop our body in space) is an important factor in order to play the piano well. However, people on the ground mostly ignore stabilizing activity, even though they are keep doing it while they do some activities. Many people end up stabilizing their body with excess muscle contraction (tension). Why? This is because people tend to depend heavily on muscle contraction to stabilize their body without trying to utilize friction enough. As I said before, we forget these forces are there and don’t try to utilize them fully. The first thing we should use to stabilize our body is this frictional force. Without the frictional force we cannot stop our body. Friction makes the support part (the contact part) stop. Then, we use muscle contraction to stabilize the body above of the support part. If we do so, we will have possibility to recruit less muscle contraction.

We still receive friction force by contacting the ground, even though we usually don’t realize them. So, we could stabilize our body with giving a certain degree of muscle contraction (with unknowingly using friction) and succeed the task. Since we succeed the task like this, we usually don’t review how we did it. In most cases we have alternative way to succeed the task, which involves less muscle contraction through utilizing ground reaction force and friction. However, we usually don’t take alternative way. We know this kind of phenomenon: this is “end-gaining”. So, our stabilizing activity itself tends to fall into end-gaining pattern with depending heavily on muscles. This is why many people end up giving excess muscle tension in their movement. This is why we tense our neck.

To make it better (recruits minimum muscle contraction in movement) we should have intention that we are stabilizing our body while we make some movement and  that we fully utilize ground reaction force and friction. We don’t have to “focus” these forces, but we just pay attention to them a bit and include into any activity.

 

photo credit: Thomas Hawk Coachella 2014 via photopin (license)









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