Basic Human Movement Principles

Biomechanics is how forces act upon the body, as well as how the body creates forces, in return. Understanding how the body generates forces, and sequentially applies them in order to produce movement, requires a fairly broad spectrum of knowledge. This includes forces of nature, human anatomy, and the combining of physical laws with the structures of the body.

An understanding of biomechanics helps us understand how the body should move. And, once we know how it should move, we can hopefully recognize when it is moving incorrectly. We can also gain an understanding of what causes the correct movements to take place. And, once again, we should then be able to recognize when incorrect movements are taking place, and determine the appropriate steps to rectify this.

Laws of Motion

To understand how the body works, we first need to understand the laws of nature that act upon it. The most important of these, for exercise purposes, are newton’s 3 laws of motion, and gravity.

Newton’s 1st and 2nd Laws of motion

The 1st and 2nd laws of are probably the most important, in terms of creating movement in the body. The 2nd being how muscles act on bones, across joints to create the action of movement, itself.

1st law: “inertia”

A body will remain in a constant state of motion, if no forces act upon it.
This means that if something is keeping still, and no forces are placed unto it, it will remain still. Similarly, if it is already moving, it will keep on moving.
Where this applies to the body, is that no movement will occur, without some force acting on the body. So, without muscular contractions, to cause movement, or gravity to pull down on the body, or an external force (such as collision with another object), there will be no change in movement.

2nd law: “acceleration”

A force acting on a body will cause a change in motion directly proportion to size of the force, and in the direction of the force.
This means that when a force is applied, whatever it is applied to will begin to move in the direction of that force. It will also have a rate of change of movement, depending on how much force is applied, and for how long.
For the human body to create movement, forces must be applied in the form of muscular contractions, which in turn move our bones in sequences that result in the gross motor movements that we see. For example, contractions of the muscles of the legs and hips will cause walking.

3rd law: “action and reaction”

For every action, there is an equal, and opposite, reaction.
This means that for every force applied, the exact opposite force is applied in the opposite direction.
In movement, this means that for every force the body imposes, there must be something imposing the same amount of force back onto the body. If we keep with the example of walking; the force applied by our feet, to the floor, is counter-acted by an equal force by the floor onto our feet. So, as we push back, the floor pushes us forward.


This universal force acts on all things, at all times. And, we mere humans are no exception. All day, every day, we are being pulled down to the ground. If you don’t agree, try jumping as high as you can, and see what happens…
A large majority of the movements we make, and the forces we apply with our bodies, are done against the force of gravity. A perfect example of this is lifting a weight, in the gym. When you perform any weight training exercise, the force you are working against, is gravity. It’s even right there, in the name. “Weight” is the force of gravity, pulling down on a mass, or body.