Tension

Introduction

Tension forces are oriented primarily parallel and in line of an object in opposite directions. The result of tension forces is ranged from fine material elongation to total deformation and breakdown. This depends mainly on the material of the object on which tension is applied and the amount of applied tension. Tension can deform different body tissues such as muscle, tendon, ligament and neurological tissue. In Physics, Static tension test determines the breaking point of the material and its elongation, designated as strain which is the percentage of change in length per unit length. For example, a 100-millimetre steel bar elongates 1 millimetre under a given load, for example, strain is (101–100)/100 = 1/100 = 1 percent.This page will explain the tension forces and their consequences on different body materials.

An image shows the difference between compression (left) and the tension (right).Note:(-ve) sign indicates an equal opposing force and the arrows indicate the directions of forces applied

Tension generation inside human body

Most of body tissues are susceptible to tension which are forces that met by resistance against lengthening. Tension forces can be external from outside the body, like passive stretches to muscles or skin tugging or the can be internally generated like the effect of the muscles on themselves or neighboring tissues.

Does Tension protect tissues or harm them?

It is widely known that overload with “tension” may lead to ligament sprains, muscle strains and in some cases peripheral nerve injury. Examples: hamstring tear, patellar tendinopathy, brachial plexopathy, MCL tear. Insufficient loading leads to muscle atrophy, and weak ligaments and tendons. So, Both of overloading and insufficient loading damage tissue structure and function in some way. However, the correct tension loads help tissue function and protect tissue structure taking into our consideration the following examples of biological facts:

• Lung epithelial lining must have what is called cyclic tension that decrease or increase according to the breathing phase. If this cyclic tension disturbed, it can lead to fibrosis or emphysema.
• Muscles exert tension on tendons to generate contraction causing movements for function execution or strengthening or other purposes. Disturbed tension can lead to tendinopathy or strains or weakness. Muscle tension-length relationship is a widely known principle for efficient muscle function.
• Tension drives faster wound healing so less infection hazards but the risk of hypertrophic scarring increases

Actually, these tension forces are called macroscale tension forces, and it means they affect the tissue as a whole but what about the microstructures of these tissues. Do they have a role? Interestingly, Cellular constituents and structural building of different tissues play role in withstanding tension and here we call tension forces as microscale tension forces. The successive examples highlight this role in some way:

• Myofibers ,or the muscle cell, consists of actin polymers and myosin polymers together with other proteins that collectively form a contractile network which can generate or sustain tension.
• Stretch-activated ion channels in cochlea, smooth muscle, hair follicle cells, small intestine epithelial cells and cardiac tissue. These channels are composed of proteins with a hollow channel that opens upon tension. Ions flow rapidly through an open ion channel, causing immediate changes in transmembrane potential and allow for rapid signaling milliseconds responses.