To understand why optimal mobility is so critical for us, we need to know exactly what mobility is. Mobility is defined as: the ability to move or be moved freely and easily.
We know we should have optimal mobility, but do we really understand why we have to have mobility to have optimal function? A major factor is because humans don’t exist in isolation; we interact with the world around us. For us to truly understand why mobility is so important we need to have a grasp on the science of the physical environment in which our bodies exist and function in. Understanding our physical environment will only empower us, enabling us to recognize the importance of how optimal mobility enables us to have the ability to optimally function.
We interact with multiple forces in the physical environment that our bodies function in. Understanding Newton’s Third Law is crucial. To simplify, I break the Law into 3 parts. Part one of the Law states: forces always come in pairs: equal and opposite action-reaction force pairs. For instance, we know that with everything we do our bodies have to deal with the force of gravity. Gravity is the force that attracts our bodies towards the center of the earth. Often, we forget about its opposite action-reaction force; ground reaction force (GRF). To understand human biomechanics it is essential we first understand the interaction of forces in the physical environment that human biomechanics occurs in.
Everyone knows gravity, and if you are clumsy like me, have probably experienced it firsthand by falling a time or two. We blame gravity for the fall, but gravity is not acting alone. We experience gravity during the fall but when we make contact with the ground our body experiences the interaction of gravity with GRF. It’s this interaction in time with gravity and GRF that we physically feel the pain from falling. If we drop a glass, gravity alone does not break it. Gravity’s interaction with GRF with the glass cup and the ground is what shatters it. Other factors obviously go into the equation like mass, velocity, direction, etc., but the main focus here is to understand action-reaction forces.
Lucky for us when we fall, we are not as fragile as the glass. A simple, somewhat comparable object to humans would be a basketball. When the basketball makes contact with the ground we know that gravity and GRF interact with ball and the ground. In physics this is defined as the moment when a pair of forces (gravity and GRF) are acting on two interacting objects (the basketball and the ground). This is where we need to understand part two of Newton’s Third Law which states that: the size of the forces on the first object (ball) equals the size of the force on the second object (ground).
We have seen this Law simply stated as: for every action, there is an equal and opposite reaction. When the glass interacted with gravity and GFR at the ground and shattered, it was due to the fact that the glass did not have the ability to transform the energy of the interaction, so therefore it simply breaks. When the ball interacted with gravity and GRF at the ground it bounces back in the opposite direction (that is if it is properly inflated) due to its ability to transform the energy from the interaction of the forces at the ground. We can experience this equal opposite reaction force when we start to bounce a ball with more force into the ground; it comes back with the same increased force.
The reaction of the ball bouncing back into our hand enables us to understand the third part of Newton’s Third Law which states: the direction of the force on the first object is opposite to the direction of the force on the second object. The ball left our hand into the direction of the ground. Following its interactions with action-reaction forces at the ground, the ball’s ability to transform the energy from that interaction enables it to bounce back and travel in the exact opposite direction of the ground, returning back into our hand.
To better understand the physical environment, we need to understand one more Law of physics which is: The Law of Conservation of Energy. The Law states that: energy cannot be created or destroyed, but only changed from one form into another to transferred from one object to another. For example, when the glass made contact with the ground, the energy from the interaction of forces shattered it and no energy was lost. When the ball made contact with the ground, the energy from the interaction of forces was transferred from the ground into the ball, enabling it to bounce back into our hand. Another we have seen on desks is Newton’s cradle pictured to the right, where the energy is continuously transferred.
In the physical environment in which we exist, these two Laws work in conjunction to enable efficient human function. Lenny Parracino, Fellow of Applied Functional Science at the Gray Institute, articulated it by stating that:
“We need energy to move. Energy allows work to occur. Work is the function of forces. Forces change the way we move. If we want to stop and change direction, we need to exert a force. But we cannot exert a force unless we have energy.”
Just like the example of the basketball, in gait when our foot comes in contact with the ground, we are able to transform the energy of that action-reaction interaction of forces to propel us into walking. However, if we lack optimal mobility in the foot/ankle complex, the transformation of energy will be inefficient. Lenny Parracino calls the inefficient transfer of energy through our bodies “energy leaks”. Optimal human function in the physical environment can then be defined as efficient energy transformations during biomechanics where no energy is “leaked”.
Optimal human function in regards to the interaction with the physical environment is for the body to possess the ability for the energy of action-reaction interaction forces to enter into the system and efficiently travel through the body. If we have optimal mobility in each joint, as the energy travels through those joints, motion in 3 dimensional space will occur. Joints are not isolated but integrated. An action or lack of action in one joint creates a reaction or lack of a reaction in the other joint(s) which articulate to it in the kinetic chain. In other words, each joint plays a role to each other and to the body as a whole.
If we lack mobility in a joint, there will be stillness. As motion and energy enter into the immobile joint, injury and trauma to the joint and surrounding tissue is likely to occur. If the force entering the immobile joint exceeds the individual’s adaptive potential, injury is very likely. This lack of the energy to be able to efficiently travel through the body is an example of an “energy leak.” When the joints in our body lack the ability to transform energy efficiently, our joints function more like the glass than the ball in the previous examples. In the athletic setting, these inefficiencies greatly reduce one’s athletic potential.
By understanding the physical environment that human biomechanics occur in, we can understand why we need to possess optimal mobility to have optimal function. The objective in human function is to strive for efficiency instead of just being effective. Therefore, we need to identify any inefficiencies and address them to not only prevent injury but to optimize performance.
Just like gravity works as a pair with GRF, mobility works in unison with stability. That is why I stated optimal mobility is needed for efficient human function. Just as too little mobility is not good for the system, too much mobility is also harmful. What is needed is the optimal amount of both mobility and stability. The structures need to be mobile enough to move while at the same time being stable enough to return. We do not want to create mobility in a structure unless at the same time we are creating stability. It would be illogical to create motion and flexibility if we cannot control it. Mobility without stability is the definition of injury. You would be able to move in one direction but due to the lack of control, would not have the ability to stabilize and transform to move in a different direction.
– During a conversation over two years ago, Louie Simmons of Westside Barbell gave me a Basic Physics book (pictured left) that would forever change my perspective and understanding on both treatment and training. I am forever grateful.
– I want to credit the Gray Institute for furthering my eduction and understanding of human function.
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– John Quint NMT ART CAFS