All life forms on earth are under the influence of gravity, which is an external, constant, and downward directed force. Tensegrity (or tensional integrity) is a concept that you can use to view how all structures (our bodies included) are supported. It describes two very important types of forces of mechanical physics that give a structure support: compression and tension.

Compression:

“Compression is the force that attempts to shorten or squeeze a body or object.”

Gravity is an external compressive force that is always acting on you as the internal forces of your body meet it to create equilibrium. Everywhere from the soles of your feet, to your intervertebral discs, to each cell in your body is under this compressive stress. In fact, you are taller at the beginning of the day than you are at the end of the day because of the compressive stress that your body is under when you are upright throughout the day. At night the compressive stress on you axially is minimised as you lay perpendicular to the downward force of gravity and your spinal discs and bones stretch back out.

Your body's intervertebral discs and bones are a good example of structures that can withstand this compression force well, just like the pillars on a bridge.

Tension: 

“If compression is the force that attempts to shorten or squeeze the body, then tension is the force that attempts to stretch or elongate the body.”

When you pull on an elastic band, the force you observed as you pull is called tension. Different materials offer different strengths and weaknesses to either compression or tension. For example, rope can support very high tension forces, yet if you compress rope the opposite direction, it crumples. In the same way, a marshmallow can be compressed compactly, but if you pull it apart, the marshmallow will rip easily.

Compression and Tension:

On a suspension bridge, there are the pillars that are compressed and there are cables and suspenders that are ‘under tension’ to help keep the overall structure supported. Your body reflects this difference in material, function, and support by using the positioning of your joints and the shape of your bones for compression and the use of your muscles and soft tissues for tension. 

This harmonious interplay between soft tissue and hard tissue is what we are looking at when it comes to the analysis of biomechanics and the potential dysfunctions that can surround movement. What tensioning strategies is that body using to create support and stability (i.e. what muscles are being engaged and how).

If there isn’t enough tension coming from one area of the body to create stability, it has to come from another area. For example when a stabilising muscle isn’t working enough to create tension, another will work in its place. This compensation adds extra stresses to particular parts of the body and is what is generally described as a ‘muscular imbalance’ or an ‘open chain fault’. 

This increases the chances of an injury occurring as the physiological impact of over-tensioning is prolonged (overuse injury) or the position of the joint is suboptimal for the forces placed on it and an acute injury can occur (sprains etc). This may also have downstream effects as other joints and systems of interplay become compromised as a result as well.

Note: there are also torsion and shear forces in mechanical physics which are hugely relevant as well.