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Biomechanics Explained – The Science of Movement

The study of anatomy and how the body works has fascinated the human race for centuries. One of the fundamental aspects of being human is how we move and interact with our environment.

From the Ancient Egyptians and Greeks to Leonardo Da Vinci, Galen, John Hunter and modern scientific laboratories around the world – the study of anatomy and how the body works has fascinated the human race for centuries. One of the fundamental aspects of being human is how we move and interact with our environment.

“We too are in perpetual motion. Everything in us from birth until death moves and changes. The processes of growth and aging are the clearest illustrations of this fact. To become aware of our own evolution, of the rhythms we are subjected to, of the movements that imprint themselves in us of the different interconnections that make up a living body, is to learn to know and take care of ourselves so we can go through life in greater harmony.” 

Jean-Pierre Barral D.O. (Understanding the Messages of your body, 2007)


The human body is unique from other animals for a few reasons. Firstly, we are bipedal which means that walking and running in this pattern is our primary form of locomotion, unlike other bipedal animals such as birds and kangaroos, which fly and hop respectively. Secondly is our fine motor coordination and ability to manipulate objects in minute detail on both a large and very small scale.
Like all other objects on earth we are subject to gravity and other forces both within and outside our bodies plays a role in our posture, movement and coordination. We, as humans who complete multifunctional tasks, are also required to transfer additional loads to our body weight such as: carrying groceries, picking up cutlery to eat or playing sports while maintaining a posture to keep us in a certain position.


Biomechanics is the study and explanation of how these movements occur. Understanding both the correct biomechanical patterns and faulty ones are an essential part of physiotherapy. Biomechanics explains the complex and finely coordinated interactions of bones, muscles, ligament and tendons.

The word Biomechanics can be broken down to understrand it better: 

Bio – rooting from biological: life and the study of it
Mechanics – from the root word mechanica: the mathematical doctrine of motions of systems under the influence of force and constraints.


This study has been more recently applied to the viscera (organs) and has filled in a long missing link in how our bodies move and function. You can read more about this in the introductory article on Visceral Manipulation here. By understanding how the body should function we can pinpoint any dysfunctions that cause disease, degradation, instability or movement abnormalities that cause a decreased quality of life or injury in patients. This understanding then helps us to perform the correct treatments and provide the right exercises to rehabilitate the body after disease or injury. It assists us in preventing injuries by correcting abnormalities before they cause major problems. There is no area of human function that does not apply the principles of biomechanics, in this article we will look at the basics required to help you understand your body and look after it properly. This article is a general overview only; separate joints, structures and organs will be addressed in their own articles.


To understand the basics of how our bodies move we need to understand some basic principles of biomechanics. These principles help us describe the movement and understand the effect on the body and the effort it takes to move or manipulate objects. In this article we will look at two categories:

  1. Planes and general types of movement
  2. Forces acting on the body and joints.

Planes of Movement

It is important to understand the planes in which your body and specific joints are divided. It will make the understanding of the interactions between joints and muscles in a movement such as a golf swing easier to understand. Complicated movements do not happen in a 2 dimensional plane; therefore the body has been divided into different planes to understand the science of movement better.

There are three main or cardinal planes of movement; all other planes are subdivided from them. The first plane is the Sagittal Plane and it divides the body into left and right halves. The types of movement that happen in the Sagittal plane are flexion and extension or bending and straightening. The second plane is the Frontal Plan and divides the body into front and back halves. The types of movement that occur in the frontal plane are abduction and adduction or moving towards and away from the midline. Lastly, the Transverse plane divides the body into top and bottom halves. The movements that happen in the transverse plane are internal and external rotation or turning towards and away from the midline. Each plane has an axis that runs perpendicular to it and is the axis around which movements in that plane occur. You will recognize the names for these movements in the exercises that your physiotherapist gives you such as; shoulder external rotation, knee extension or hip abduction.

Forces on body

The human body, like all objects on earth, is subject to gravity and thus most functional movements occur against gravity. This means that even when sitting or standing still you still need to produce enough resistance and stability in your body to not fall over or be squished down. This might sound silly, but did you know that you are approximately 1 centimetre taller in the morning after you have been lying down all night? This is because when you are lying down there is no gravitational force compressing your joints and your spine allowing the shock absorbing structures like your spinal discs to expand to their natural size.

Newton’s Laws of Motion plays a role in the movement of the Human Body:

  • The first is the law of Inertia; that an object at rest will stay at rest unless acted on by and outside force. The converse also applies in that an object in motion will continue moving unless acted on by an outside force.
  • The second law is the law of acceleration; the acceleration or speed of an object is directly proportional to the force acting on it and inversely proportional to the mass of the object.
  • The third law is the law of action and reaction; where there is an action there will be an equal and opposite reaction.

As with gravity we can’t escape these laws of motion, which means that our bodies need to be able to counteract them or use them to our benefit.

Posture

Posture is how we hold and carry ourselves in space. There are two types of posture: static and dynamic posture. Static posture refers to our body alignment in stationary positions such as lying, sitting, standing or kneeling. Dynamic posture is our body alignment while moving and is a little more complex than a static posture. Dynamic posture is required for stability during movement against gravity and through a changing base of support, while static posture is mostly only subject to gravity and has a clear alignment that doesn’t change. Dynamic posture is present in anything that requires movement like walking, running and more complex motions such as dancing.

Joints

There are 206 bones in the human body and they are all designed to fit together perfectly at the joints in order to provide the movement required by that specific joint/body part. The joint or articular surfaces of each bone and how they join together can be described with the same terms that are found in mechanics elsewhere such as cars, heavy machinery and carpentry. The type of joint will tell you what movements it can perform.

There are three large categories of joints which are: Synarthrodial (immovable) joints, these joints are found in the skull and tooth sockets. Amphiarthrodial (slightly movable) joints – these joints are found in the ribcage, pelvis or lower leg between the Tibia and Fibula. And Diarthrodial (freely movable) joints. Synarthrodial and amphiarthrodial joints’ purpose is toward stability in the skeleton. Diarthrodial joints are the joints that allow us to move and are generally where injury or dysfunction occurs.

There are 6 types of joints in this category: Gliding, Hinge, Pivot, Condyloid, Saddle and Ball & Socket joints. Below is a table that further describes these joints.

As you can see there is a wide range of mobility in joints all over the body. The stability of joints is defined by how much of the bone surfaces are in contact with each other. The more bone contact the more stable and the less contact the more mobile the joint. All joints are surrounded by capsules and ligaments which increase their stability, while muscles and tendons provide mobility and force.

Muscles

Muscles, like bones, work together with other muscles to create movement. The action that the muscle makes is called a contraction. There are two main types of contraction: isometric and isotonic. In an isometric contraction no movement happens such as, pushing against an immovable object like a wall or the floor. Another example is when there is an equal resisting force present such as that tense moment in an arm wrestling match when neither opponent’s arm moves. Isotonic contractions on the other hand produce movement and can be divided into concentric and eccentric sub-types of contractions. Concentric contractions shorten the muscle while eccentric contractions lengthen the muscle. These two actions always occur hand in hand, meaning that muscles always work in teams. These teams are called agonist and antagonist pairs. The teams allow for movements to be smooth and controlled against gravity or other external forces. During movement the agonist muscle performs a concentric (shortening) contraction and the antagonist muscle performs an eccentric (lengthening) contraction. The concentric action produces the force required for movement while the eccentric controls the movement against gravity and other loads. This means that both muscle groups in the team need to be strengthened or else there will be an imbalance. To look at a practical example, a bicep curl should be done in a slow controlled manner on both the lift and lowering of the weight. If the weight descends relying more on gravity than an eccentric contraction of the biceps you will build strength but not control and the eccentric muscle group will not work as it should (basically only training half of the required muscles).

The skeletal muscles in the body can be divided into two main groups depending on their function. These groups are stabilisers and mobilisers. Stabilizers are generally the deeper intrinsic muscles which help to keep the body stable during movements. Mobilizers are generally the larger, more visible muscles and generate movement in the body. However, these are only loose groupings as all muscles can perform a stabilizing and mobilizing function, but it is important that muscles are conditioned for their primary function.

Fascial Slings

Fascia is a thin connective tissue that is found everywhere in our bodies. The main purpose of fascia is connecting tissues and cells together and preventing friction between them as we move. When it comes to biomechanics -fascia actually facilitates motion. These motion chains are called slings and they provide both stability and generate force for movements. This is because the fascial connections between body structures and parts facilitate the body functioning as a whole. Many people have wondered why when you visit your physiotherapist for back pain they sometimes work on your leg first, as well or even only! To only treat the pain and not the source of the pain is not effective. We have to consider the whole body every time there is an injury/pain.

Below are some of the main fascial systems found in the body but they don’t stop there. Knowing about fascial slings is very important, as a dysfunction can happen in one area and cause an injury somewhere else. If the dysfunction is not treated the injury will never go away.

Conclusion

This article has been a very basic introduction in biomechanics and understanding how our bodies move and function. To understand movement, we always have to consider the science behind it. There are a lot of complicated movement, control and activation that occurs even with the simplest of activities. It is also important to consider that injuries or incorrect angles at joints in one area could affect lots of other areas. Below is a diagram of all the interlinking systems and tasks the body uses to perform physical function. There are six key aspects of physical function that all have an effect or play a part in human biomechanics. None of them can be completely separated from any of the others. Any assessments for injuries or prevention of injury or disease needs to take into account all of these aspects to ensure that the injury is not just treated, but a long term goal of eliminating the source of pain/injury has been addressed.

Speak to your physiotherapist today about a biomechanical assessment and remember to tell them about previous injuries as these may be the key to overcome your current obstacles.