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Biomechanics: The Science of Human Movement

Biomechanics: The Science of Human Movement

As athletes it is important for us to have a basic understanding of kinesiology and biomechanical principles.  We should know how movements impact posture, body mechanics, our muscle system, and the training and sports that we participate in.

Biomechanics is the study of movement involved in strength exercise or in the execution of a sport skill.  Biomechanics focuses on the physical factors with movement by applying scientific laws.   With these applications, it looks at what takes place during an exercise and the role that each key joint and muscle plays.  The scenic laws incorporate such physical factors as speed, mass, acceleration, levers, and force of the particular movement.  Biomechanics explains the “why” of a movement and “how” the movement can be improved through science-based modifications.

Kinesiology is the study of human motion and mainly focuses on muscles and their functions.  It is the study of human movement, performance, and function by applying the sciences of biomechanics, anatomy, physiology, and neuroscience. It looks at movement and which muscles are involved to create movement relating to strength exercising and sports technique.

Together, kinesiology and biomechanics can help you determine what exercises are appropriate, how to create a workout plan, the effectiveness of your execution of the exercise,  and how safe they are for the sports that you participate in.  Biomechanics is the execution of doing an exercise most effectively, while kinesiology tells which muscles are involved in the particular actions.

Biomechanics 101

As an athlete, having an understanding of our joints, muscle structures, and the actions of our muscle structures will lead to a better understanding of what is happening to our body during training and exercise.  Having an understanding of the mechanics and physical factors of our exercise movements will help us realize how effectively and safely we execute our exercises.  The following are the key concepts of biomechanics.

The Key Concepts of Biomechanics

There are many key concepts that I will discuss below.  This discussion will take you back to your Physics I  days (without all the calculus).  The key concepts of biomechanics involve stability, force, angles, mass, work, inertia, acceleration, gravity, levers, torque, and even Newton’s Laws of Physics.

Sir Issac Newton


Stability is necessary for safety in almost every exercise that we perform.  The concept of stability is that the larger your support base is the greater your stability.  This is true when lifting weights, where for most exercises you want to have your feet spread apart about shoulder width.  To increase your stability even more you can bend your knees slightly.  The lower your body is the more stable it becomes.  Hence, bending your knees lowers your center of gravity and you become more stable.  I have seen many people bench pressing free weights (yes, I was once a gym rat) with their feet on the bench rather than on the floor.  This position is not stable and can lead to serious injury.  The proper position that provides stability is to have your feet flat on the floor.


Force is an action that causes motion and are in the push or pull type of motions.  Only muscles can create the force needed to put an object into motion.  When the human body is moving weight in strength exercises there are four components that make up force.

1) Magnitude: Or the force applied.  If you want to lift a 50 pound weight, you must apply a force greater than 50 pounds to lift it.  Actually, you need to apply more than 50 pounds of force because you need to overcome the weight of your limbs and body, and you must overcome resting inertia (the resistance of any physical object to a change in its state of motion ).

2) Direction: The force must have direction.  This is seen in sports like swimming, running, and throwing activities.

3) Point of Application: This is where the force is applied on the body or instrument being used.  In bench pressing with free weights, you apply force using your hands at two points to raise one bar.  Where you are gripping the bar is the point of application of the force.  For sports that require an instrument such as a bat or a racket, the point of application for the force is where the ball hits the instrument.  Lastly, for sports that require you to throw an object, the point of application for the force is where the hand or fingers are in contact with the projectile.

4) Line of Action (or Force): The line of action is a straight line drawn from the point of application of the force through the direction of the force.  Performing a squat is a good example of the line of action.  While performing a squat, the line of action goes through the center of the body.  If you do not have proper technique while performing a squat you can actually have the line of action shoot out your knees.

The Angle of Muscle Pull

When you perform a strength exercise (such as a bicep curl) the strength exhibited at different points in the range of motion will vary due to the angle at which the muscle pulls.


There are two types of inertia: 1) resting, and 2) moving. Both described with classical physics Newton’s First Law of Motion

1) Resting Inertia: Newton’s First Law of Motion and resting inertia.  It states that when an object is at rest it will stay at rest unless acted upon by some outside force.  So, a dumbbell sitting on the floor has resting inertia.  For you to be able to pick it up you must apply a force greater than the weight of the dumbbell itself.

2) Moving Inertia: Newton’s First Law of Motion and moving inertia. It states that when an object is in motion it will stay in motion unless acted upon by some outside force.  So, once you pickup the dumbbell and set it into motion it will continue on its own accord without any additional application of force.  Though the heavy weights are moving, they quickly stop because of the effects of gravity.  Let’s try to bring the example to real life exercising.  When performing lateral arm raises with really light weights, you experience on the upward movement as an effortless feeling of flying.

This is an important concept to think about.  If you are moving a weight too fast, the force required to stop it at the end of the range of motion may be too great for your limbs.  If you are not capable of creating the stopping force injury will occur.

Also, when lifting weights, the future away the mass of the object, the greater the inertia.  This make a moving weigh more difficult to control.  Therefore you should always position yourself as close as possible to the weight you are lifting.

Force, Mass, and Acceleration

Newton’s Second Law of Motion explains force and its relationship to mass and acceleration.  Newton’s Second Law of Motion states: that in order to create a force you must place a mass into motion with acceleration and a change in velocity.  M x A = F or Mass multiplied by velocity (acceleration) equals momentum (force).

Newton's Second Law

At the gym momentum occurs in exercising machines with cable attached to the weights.  When performing the exercise you adjust the speed of your movement to how fast the weights move up and down.  If you do this in an uncontrolled fashion and create a fast upward accelerations, you can cause the weights to continue in an upward motion while you have already stopped.  The point is that when your muscle generates a force there must be an acceleration of the weight.

Another way to think about this is that when you start an exercise you must generate force.  Once you have taken the stationary weight and begin movement you have accelerated the weight.  Once the weight is in motion it only has velocity.  You are no longer creating a force unless you are changing the speed of the object.  In other words, you must place the weight into acceleration to get it moving.  Once the weights are in motion, they have momentum.


The formula to measure work is W = F x D, where W = work, F = force, and D = distance of the object being moved.  In an isometric contraction there is no movement, there is no work being done.  For work to be done there must be movement.  It is not to say that energy is not being used.  Energy is more physiological, while work is more mechanical.


Power is defined as work done in a unit of time.  In exercising, the amount of power generated depends on the amount of time it takes to accomplish the work.  The faster you work, the greater amount of power.  The slower you work, the less the power.  So, in weightlifting terms a weightlifter has great power, whereas the powerlifter has great strength.

Equal and Opposite Reactions

This is known as Newton’s Third Law of Motion. This law states that: objects in contact exert equal and opposite forces on each other.  An example would be when you are doing a push-up, you must push against the floor with your hands while the floor in return pushes against you.  The result is that you raise up completing the push-up.


Levers in the Human Body

A lever is defined as a rigid bar that turns about an axis of rotation or fulcrum.  In our body our bones act as the bars, our joints represent fulcrums, and our muscles contractions is the force. A lever provides strength or improves the range of movement.  The strength and range of movement of a muscle depend on the positions of its insertion relative to the joint.  The farther away these two points are the greater the strength of the muscle contraction.  Lever systems have three possible arrangements: 1) First-Class Levers, 2) Second-Class Levers, and 3) Third-Class Levers.

1) First-Class Levers: The first-class lever is a simple seesaw configuration.  It has its fulcrum between the force and the resistance. Nodding the head is an example of a first-class lever in the body.  First-class levers do not create a great amount of force.  However, they do produce a maximum range of motion and speed of movement.

2) Second-Class Levers: In the second-class lever, the weight is distributed between the fulcrum and the application of force.  This lever is best for the gain of force.  An easy visualization of a second-class lever is a wheelbarrow. And for a visualization in the human body, a second-class lever is when you stand up on your toes.  This example of a second-class lever is utilized for running and walking.

3) Third-Class Lever: In the third-class lever the force is applied between the fulcrum and the resistance.  This is the most commonly found lever within the human body.  For example, in the bicep curl, the bicep muscle inserts (is attached) about one inch below the elbow joint.  The point of attachment is the point of application of force. The elbow is the axis of rotation (the fulcrum) and the resistance is the forearm and the weight being held.  In this example, the distance from the point of application to the fulcrum is very short, and the weight is far from the application of force.  This makes the system mechanically inefficient.

Wheel and Axel

The wheel and axis type arrangements in our body are needed for the transmission of force.  An example is the shoulder joints medial and lateral rotation.

Pulley Systems

In the gym pulley systems are very common.  In the human body an example of a pulley system is our knee joint working along with the patella.


Torque is the magnitude of twist around an axis of rotation (fulcrum).  Torque (twist) is rotary (angular) movement in any plane about an axis.  Torque is seen is virtually all movements in the body.  When torque is produced, the force is applied at some distance away from the axis of rotation.


This is a pushing movement in which the hands or feet move in a straight line while still engaging a rotary component of movement.  These movements include the leg press and overhead press.


This is just the opposite of pushing.  The hands and feet move in a straight line while two or more joints are in rotary action.  An example is the seated row.


Gravity is the downward pulling force that creates resistance.  In exercise, the effects of gravity are demonstrated when using free weights.

Center of Gravity and Line of Gravity

The center of gravity is the point in your body which your weight is equally distributed.  This point is usually located in the hips.  When you drop a straight line down from the center of gravity it is known as the line of gravity.  It should fall within your base of support.


Kinesthesis is the ability to perceive your position and movement of you body’s limbs in space.  To do this, your body uses various receptors in the joints, muscles, and tendons.  In the tendon, the Golgi tendon organ is the receptor that sends signals back to the brain on the activity of the tendon.  It acts as the safety valve so the the joint does not hyperextend.  There are also receptors in the joints and ligaments that send signals to the brain about changes in position, speed or movement, or the acceleration of the limbs that occur at the joints.


Vision is used for balance.  When you focus on an object during exercise it enables you to have better balance and orients you to your surroundings.  When focusing on an object for balance, you should not use an object that is in motion because movement of your head also relates to the balance mechanisms in your ears.

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