"And Enoch walked with God: and he was not; for God took him." (Genesis 5: 24; The Holy Bible, King James Version)
"And in the fourth watch of the night, Jesus went unto them...walking on the sea." (Matthew 14: 25, 29; The Holy Bible, King James Version)
"Then one of the two women came to him walking bashfully." (The Koran, The Narratives 28.25)
"Let my legs be to me that I may walk therewith." (Egyptian Book of the Dead, First Level of Khert-Neter)
As you can see from these sentences, we as children of deity or of religious belief have been walking for a very long time. I cannot explain how Jesus walked on water. Some say that the sea must have been partially frozen, but that is a debate for another time.
What I am about to "walk" you through is a discussion of the basic biomechanical application of walking. Bringing in the kinesiological or kinematics aspect among the biomechanics properties is the main goal and focus of this report.
The word walk has many different meanings and associations for people of many races and cultures. It also has multiple synonyms including saunter, stroll, gait, march stride, pace, toddle, and even locomotion.
Locomotion, as described by Lexico Publishing Group, LLC, for Dictionary.com, "is an act or the power of moving from place to place: progressive movement (as of an animal body)."1 Dictionary.com also says this about walking: "To move over a surface by taking steps with the feet at a pace slower than a run."2 So if we put these two together we come up with the definition that walking or running is an act or power of moving over a surface with the feet from place to place.
Walking is one of the simplest events in adult life unless otherwise injured or incapacitated; yet in a scientific aspect, it is one of the most complex motions in the world, or even in the universe. Walking is widely studied, but often shows a frustrating aspect of natural science. We find this true when we attempt to understand how the subdivisions of the human body systems interact to generate walking. The human structure and the functions of the system workings become progressively more complex, making it complicated to discern common and collective principles.
One way of studying the act of walking is to gradually go from a level of "the body as the whole" toward a level of sub-systems and secondary sets of body functions underneath "the whole" organizational system. As we have stated in class, sometimes when we analyze someone or something, we have to take the whole picture and break it down into smaller chunks. Sometimes if you check out the small stuff or correct the small stuff, it helps to improve or correct mistakes, or just simply gives you the answer you are looking for.
If we take this approach when we do the analysis, we can begin to see pertinent information from the higher levels of the organization. This can help guide the search to understanding the biomechanics of walking and running at more complex levels of the organization.
The human body on average has over six hundred muscles, and about half of them will be moving or contracting when we take the first step in just a moment. However, they will not all be moving because of the movement of the legs; some are supporting muscles, some are the concentric and eccentric muscle contractions, and yet others are used in functions secondary to the walking motion. I will not be going into too much detail on this point, but it is noteworthy.
First, I will show the pattern of walking starting with the center of mass movements during the preparatory stage or the standing stage. I will then talk about how joints affect the linear rotation during the start of the walking phase or the first pendulum of the walking phase as the first leg begins it acceleration. I will then talk about the effect of gravity at the end of the fist pendulum stage as the first leg completes its movement.
In the beginning...
According to Lexico Publishing Group, LLC, on Dictionary.com, the center of gravity is "the point in or near a body at which the gravitational potential energy of the body is equal to that of a single particle of the same mass located at that point and through which the resultant of the gravitational forces on the component particles of the body acts." 3 That's a bit complicated for this work. In more simplified terms, the center of gravity is the center point of which an object has the ability to keep its balance without external forces acting upon it. Again, basically, it is the point in the body at which the mass is equally balanced or at least equally distributed.
In a human being, the center of gravity or the center of mass is stable. The center of gravity is in line under the shoulders and above the hips. This center varies depending on the specific person we are talking about. The center of gravity is still because the person is not moving. The center of gravity only moves as the body moves or the gait shifts. At this point, there is very little gravitational influence. There is only static friction on the bottom of the feet, which at this point is inconsequential until the workload has been acted upon or initiated.
The ground reaction force is the "force of the surface reacting to the force placed on it, as in the reaction force between the body and the ground when running across the surface." 4 This is an example of Newton's third law of motion: every action has an equal and opposite reaction. There is no ground reaction force when standing, as the gravity is holding the person down completely.
The linear rotation of the joints always goes to an imaginary point forward of the body as if trying to stay on a straight line. The reason for this linear rotation is that it makes the body more aerodynamic. If we did not have these natural rotations of the joints, we would simply have to move our mass at a more forceful level. The body does not have muscles that are perfectly forward or straight, because the body is not square. The muscles wrap around our skeleton, so no matter how hard we try we cannot make our muscles go straight. You might use a set of muscles to make a limb move straight forward, but the muscles do not move straight.
Next, please...
We start the first movement on the sagittal axis from the frontal plane. We see the left shoulder move anteriorly, to counter-balance the center of gravity as the right hip rotates laterally and the right knee, starting with the contraction of the rectus femoris and the activation of the vastus lateralis, medialis and intermedius, moves anterosuperior from the original starting position. This starts to raise the right knee to a ninety-degree angle, also in the sagittal direction.
At this point, the gravity of the earth is now pulling on the leg in order to bring it back to the neutral position. However, the contracting force of the muscles over-powers the gravitational pull. At this point, the axis of the lever system is at the hip joint. As I stated just previously, the force is coming from the muscle and the resistance is from the gravity and the weight of the remaining leg.
The center of gravity is now shifting more to the front of the body, trying to reestablish stabilization. The fluid force of the air, which is minimal or negligible unless in high gale-force winds, is not having any influence on the body or leg itself at this point.
As the leg moves forward, the upper body rotates back to its neutral position, but the center of gravity continues to move sagittally as it tries to "catch up" with the rest of the body, to keep balance. The balance or the center of gravity has been compromised, as the body is now only stabilized with one foot and the whole body is moving forward. This includes gravity and the weight of the leg-pulling down and pulling the body forward.
The body now has an extra force. This is like a wound-up rubber band. It is a type of extra kinetic energy, called potential energy, which will be used throughout the next set of movements.
The body thrusts forward toward the direction of the original movement. The torso moves forward beyond the supporting leg, which as been straightened, again going against a fluid movement. Unless wind velocity is high, this will produce very little drag force; if the airflow pattern becomes turbulent because of a faster movement, then the wave drag increases.
The foot of the moving leg now dorsiflexes to prepare for the landing of the foot to the ground upon the calcaneus. As the foot lands, gravity has now taken over again. The ground reaction force is at the highest at this point, as the foot comes in contact with the earth or ground. The ground comes up to meet the foot and connects with the same pressure that the foot meets the ground.
The hamstrings now activate and help to slow down the body in order to rebalance. The body recovers from the gravity and from the weight of the body coming onto it.
This then brings us to the first coefficient of restitution. The body has an amazing ability to bounce back, or spring back, to the original shape as the body finishes the first portion of this skill. This is called resilience. Like a rubber ball, the body has a set rule as to how much bounce it is allowed to have. Too much rebound of bounce would change the character of the body being acted upon. This would result in damage or broken parts.
With all these motions coming on as the body begins to rebalance and come back into alignment, static friction is, as before, almost non-existent. The body is now in going to be invaded by another upset. During the ending of this phase, the center of gravity is still moving, to make sure that balance stays restored. As if that wasn't enough work, here is some more for your brain...
Not again...
During the gate transition, the center of gravity slows and becomes more stable. This is important as the left leg, now starting with the hip and using the iliospoas, hip flexors, tensor fascia latae and sartorius muscles, brings the left leg forward on the sagittal plane to speed up the back leg, to bring it forward in order to help try to keep the balance.
As the left leg starts to come under the body, it comes at a slight angle to allow the free swing of the leg to move smoothly under the body to start the forward swing.
We would see the right shoulder move anteriorly forward in order to counter-balance the center of gravity as the left leg starts contracting. This starts to raise the left knee to a ninety-degree angle, also in the sagittal direction.
At this point the gravity of the earth is now pulling on the leg to try to pull this it back to the neutral position. However, the contracting force of the muscles is over-powering the gravitational pull. At this point, the axis of the lever system is at the hip joint. As I stated just previously, the force is coming from the muscles and the resistance is from the gravity and the weight of the remaining leg.
As the leg moves forward, the upper body rotates back to its neutral position; the center of gravity is now shifting more to the front of the body, trying to reestablish stabilization. The fluid force is minimal. Gravity takes over and the collection of the body starts at this point. The hamstrings now activate and help to slow down the body in order to rebalance. The body recovers from the gravity and from the weight of the body coming onto it.
This then brings us to the second coefficient of restitution and the final recovery phase, as the center of gravity catches up and slows down. The body comes back to a balance as the right leg now collects under the body to bring complete and stable balance.
Thus the body returns to its standing position, the place from which it began. The person has taken one simple step, which seems so straightforward that we often take it for granted. Yet as I have shown, the actual process of walking, broken down to its component parts, involves a very complex set of biomechanical actions and reactions, in order to take the step itself as well as to maintain balance throughout the movement. The human body is truly a wonderful system integrated in a manner we are only beginning to understand in terms of current scientific research.
Just think this only has to deal with the top half of the body. I didn't even get to the toes and ankles.
The reason I created this article was for myself, and to help me remember what our creator has created. To remember that there is more to the body than just the top muscles. -Michael A. Bahr LMT
Sources
1.) Lexico Publishing Group, LLC. For Dictionary.com "locomotion page" http://dictionary.reference.com/browse/Locomotion
2.) Lexico Publishing Group, LLC. For Dictionary.com "walking page" http://dictionary.reference.com/browse/walking
3.) Lexico Publishing Group, LLC. For Dictionary.com "Center of gravity page" http://dictionary.reference.com/browse/centerofgravity
4.) Clem W. Thompson II and R.T. Floyd " Manual of Structural Kinesiology" Fifteenth Edition, New York, NY (2004) page 342
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